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Semi-automatic implementation of network protocols Ford, Daniel Alexander 1985

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SEMI—AUTOMATIC IMPLEMENTATION OF N E T W O R K PROTOCOLS By Daniel Alexander Ford B.Sc.(Hons.), Simon Fraser University, 1984 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF T H E REQUIREMENTS FOR T H E DEGREE OF MASTER OF SCIENCE in T H E F A C U L T Y OF GRADUATE STUDIES (Department of Computer Science) We accept this thesis as conforming to the required standard T H E UNIVERSITY OF BRITISH COLUMBIA March 1985 © Daniel Alexander Ford, 1985 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) Abstract A compiler which achieves automatic implementation of network protocols by transforming specifications written in FDT into C programs is presented. A brief introduction to the the fundamentals of FDT, a standard language developed by ISO/TC97/SC 16/WG 1 Subgroup B for specifying network protocols, is given. We then present an overview of the compiler and discuss the problem of PASCAL to C translation. Transformation of a FDT specification into code is explained and illustrated by two implementation examples. The first example illustrates the implementation strategy by tracing the processing of a simple proto-col. The second example demonstrates the validity of using automatically generated imple-mentations by showing how a communication path was established between two hosts using code generated for the alternating bit protocol. ii Acknowledgement I wish to acknowledge the assistance of my supervisor Son Vuong and the invaluable help of Jean-Marc Serre and also the financial assistance of the Natural Sciences and Engineering Research Council of Canada. iv Table of Contents Abstract ii Acknowledgement iii Table of Contents iv Table of Figures vi Chapter 1: Introduction 1 1.1 Motivations and Objectives 1 1.2 Previous Research and Thesis Contribution 2 1.3 Thesis Outline 3 Chapter 2: F D T — A Formal Description Technique of Protocols 4 2.1 Overview 4 2.2 Module 5 2.3 Channel 5 2.4 Process 6 2.5 Refinement 8 Chapter 3: The FDT Compiler 10 3.1 The Compiler 10 3.2 Pascal to C Translation 10 Chapter 4: Translating FDT Specifications into C Code 13 4.1 Overview 13 4.2 Data Structure 14 4.3 Initialization Routines 15 V 4.4 Transition Routines 17 Chapter 5: Illustrative Implementation Examples 19 5.1 Example 1—The Hot Potato Protocol 19 5.1.1 Implementation Code 23 5.1.2 Execution Description 30 5.1.3 Transition Processing 34 5.2 Example 2—The Alternating Bit Protocol 34 Chapter 6: Conclusion 37 6.1 Thesis Summary 37 6.2 Future Work 38 References 39 Appendix I: FDT Grammar 41 Appendix II: Utility Routine Listings 49 Appendix III: Listdefs.h 63 Appendix IV: Alternating Bit Specification 64 Appendix VI: Utility Routines for Alternating Bit 73 Appendix VI: Alternating Bit Implementation Code 81 Appendix VII: Running the Compiler 92 Table of Figures Figure 1: Example Module Specification 5 Figure 2: Example Channel Specification 6 Figure 3: Example Process Specification 8 Figure 4: Example Refinement Specification 9 Figure 5: Illustration of Hot Potato Protocol Machines 20 Figure 6: FDT Specification of Hot Potato Protocol 21 Figure 7: FDT Specification of Player Process 22 Figure 8: Implementation Code for Hot Potato Protocol 25 Figure 9: Initialization Routine for hot_ref 26 Figure 10: Initialization Routine for team_ref 27 Figure 11: Initialization Routine for p!ayer_process 28 Figure 12: Transition Routine for player_process 29 Figure 13: Representation Data Structures for Hot Potato Protocol .. 31 v i Chapter 1 Introduction 1.1 Motivations and Objectives Network protocols have historically been specified in large informal documents prepared by the protocol designer. This imprecise method of specifying such a complex entity was potentially a source of problems when it came time to implement the protocol, particu-larly when done by someone other than its designer. The document might contain ambigui-ties or contradictions or it may simply be too vague. All of these inadequacies can impose implementation decisions which may or may not be compatible with decisions made for other implementations of the same protocol. Another problem of an informal specification is that it excludes the possibility of processing the protocol specification to automatically generate an implementation. In an effort to provide more precise specification techniques, various models for protocols have been proposed [Boch 80]. The two most useful of which have been finite state machine and Petri net models. In a finite state machine model the entities in the protocol (e.g. sender, receiver) are each described as state machines. In a Petri net model the entire protocol is described in terms of a Petri net. A practical formalism of the finite state machine model has been developed in the form of a PASCAL like language called Formal Description Technique (FDT) [ISO 84]. In addi-tion to providing unambiguous specifications, the programming language nature of FDT makes it particularly amenable to processing and the automatic generation of implementa-tions directly from their specifications. 1 2 Developing such an automatic implementation capability would remove the errors intro-duced by manual interpretation and implementation. Furthermore, it would allow the widespread installation of the protocol on differing machines and operating systems, subject to the availability of a translation tool (compiler) for each environment. The motivation for this thesis is the production of such a translation tool. A tool which would correctly implement a protocol specification written in FDT and be as portable as pos-sible. Achieving this goal would let installers working in different environments use the same implementation tool, thereby enhancing the compatibility of their installations and providing absolute portability of protocols at the FDT source code level. A way of approaching this goal is to use a portable high level language as both the implementation and target languages of the compiler. At present, one of the most portable languages is C [Kern 78]. Consequently, the ultimate objective of this thesis is the production of a FDT compiler written in C which also uses C as its target language. 1.2 Previous Research and Thesis Contribution There have been various attempts to produce compilers which process protocol specifications. Blummer and Tenney [Blum 81] describe one for an early version of FDT. Hanssoa [Hansson 84] describes the design of an "an integrated design environment" which provides a number of tools to aid the protocol designer and which automatically produces an implementation. George Gerber, at the University of Montreal, has implemented a compiler in DEC PASCAL on a VAX-11 running VMS and which uses DEC PASCAL as its target language [Gerber 83]. Initial attempts by the author to port this compiler to Berkeley UNLX 4.2 BSD were unsuccessful however due to incompatibilities between Berkeley PASCAL and DEC PASCAL. While it is possible to manually alter the FDT compiler's source code to con-3 form to Berkeley PASCAL, such efforts are for naught since it would still produce relatively non-portable DEC PASCAL code which again would require manual processing before it could be compiled. This lack of success in porting the compiler underscores the need for a more portable tool. By using C as both the implementation and target language of an FDT compiler, it will be as portable as is presently possible. 1.3 Thesis Outline Chapter 2 of the thesis gives an overview of the FDT language, Chapter 3 gives a short description of the compiler implemented and a discussion of PASCAL to C translation, Chapter 4 describes the technique used to produce an implementation from a FDT specification, Chapter 5 presents two implementation examples which illustrate the techniques described in Chapter 4, and finally, Chapter 6 concludes the success of the implementation and offers suggestions for further enhancements. Chapter 2 FDT—A Formal Description Technique of Protocols 2.1 Overview FDT (Formal Description Technique) is a language developed by Bochmann and ISO/TC97/SC16/WG1 subgroup B [ISO 84] for specifying network protocols that is based on the PASCAL programming language [Jensen 74]. The underlying model used in the FDT approach is one of communicating finite state automatons called protocol machines which exchange signals with each other and with their system environment. Except for intercom-munication, the protocol machines are totally independent and operating in parallel. FDT is really the melding of a state machine formalism and a PASCAL engine. This powerful combination allows the construction of extended state transition models. Such models use the variables of a programming language to augment the memory capabilities of a state machine. The net result is a powerful machine with a vastly smaller state space than would normally be possible. In FDT the behaviour of a protocol machine can be specified in two ways. Either directly by a corresponding state machine described by a list of state transitions and associ-ated actions or indirectly, by specifying a subsystem of interconnected protocol machines. The subsystem would have appropriate connections between internal interaction points and those of the enclosing machine being defined. Note that internal protocol machines are no different from any other and may themselves be specified as a composition of other state machines. The non-procedural (i.e. non-PASCAL) part of the language is concerned with the 4 5 definition of the protocol machines and their interconnections. Four concepts are embodied in the language and are combined to produce a specification. A module corresponds to a type of protocol machine. A channel represents a communication path between two protocol machines (modules). A process is a declaration of a finite state machine. And a refinement is specification of protocol machine instances and their interconnection. 2.2 Module Conceptually, each module type specified in a FDT specification represents one particu-lar type of protocol machine. The actual behavior of which will be specified directly by a process or indirectly by a refinement. As it is used in the language a module is a precise specification of the types (i.e. channel types) of interaction points belonging to a protocol machine. A FDT module specification is simply a list of interaction points. Each of which is given an identifier and a channel type in a manner analogous to a variable declaration. The example shown in Figure 1 declares a module called team. This module has two interaction points called tossin and tossout, both are of channel type toss. The interaction point tossin plays the role of "catcher" and tossout plays the role of "thrower". MODULE team; tossin : toss(catcher); tossout: toss(thrower); end team; Figure 1. Example Module Specification 2.3 Channel In the model a channel is a communication path existing between two protocol 6 machines. In a FDT specification, a channel is a precise description of the signals that may be sent via a particular interaction point by the protocol machines on either side. A FDT chan-nel specification gives names to the roles played by the protocol machines (modules) on each side of the interaction point (e.g. provider/user, inputer/outputer etc.) which serve to distin-guish one side from the other, and lists the signals, with any optional data fields, that can be sent by each. In Figure 2 below is an example channel declaration for a channel type called toss. This channel type distinguishes the two sides of the interaction point as thrower and catcher. Where the "thrower" side is allowed to send the message potato, which has two integer data fields, and the "catcher" side is allowed to send the message thanks. CHANNEL toss (thrower, catcher); by thrower: potato (thrower_team, tkrower_num : integer); by catcher: thanks; end toss; Figure 2. Example Channel Specification 2.4 Process A process defines an (extended) state machine and is the atomic specification of the behavior of a protocol machine. A FDT process specification is a list of the transitions of a state machine, a declaration of the queueing status of each interaction point declared in the associated module, local vari-able declarations for the extended state model and declaration of initial values for those vari-ables. 7 The queueing status of an interaction point states whether the signals sent via it are queued or not before being accepted by a protocol machine. When signals are not queued they are processed immediately upon arrival by the receiver (rendez-vous), even if this means suspending the processing of the sender. Each transition listed in a process consists of two parts, an enabling condition and an operation. An enabling condition is a specification of: - the present state (FROM clause) - an input signal (WHEN clause) - an enabling predicate (PROVIDED clause) - a transition priority (PRIORITY clause) Note that not all of the above need be present for every transition. In particular, if the input signal specification (WHEN clause) is absent the transition is spontaneous. There is also another clause, the ANY clause, which is to be used only in spontaneous transitions for selecting "random" values. The operation portion of each transition consists of an optional specification of the next machine state (TO clause) and the action to be performed, usually a small fragment of a PASCAL program. Figure 3 below contains a sample process declaration. It defines a process called player_process for the module type player. The process has two integer parameters team_num and player_num which are used to pass values to be stored as part of the state information of the state machine. The first statement declares that the two interaction points left and right, of the module player are to queue their signals. The next two statements declare local vari-ables and give them initial values. The rest of the process is a list of three transition specifications. The first of which will occur whenever a potato signal is received via the left 8 interaction point, the second when a thankyou signal is received via the right interaction point, and the third occurs spontaneously. PROCESS playerjprocess(team_num, player_num : integer) FOR player; QUEUED left, right; (* queuing status *) VAR (* local variable declarations *) the_team, the_player : integer; INITIALIZE (* local variable initiallization *) begin thejteam :— team_num; the_player := player_num; end; TRANS (* potato message on left *) WHEN left.potalo begin writeln('Ptayer ',the_player,' of team ', the_team,' caught a potato from player ', thrower_num, ' of team \thrower_team); OUT right, pot at o(the_team,the _player); OUT left.thanks; end; TRANS (* thanks message on right *) WHEN right.thanks begin writeln(Player ', the_player,' of team ', thejteam,' got a thankyou'); end; TRANS (* spontaneous *) provided ((the_player = l) and (thejteam = 1)) begin OUT right.potato(theJeam,thejplayer); end; end playerjprocess; Figure 3. Example Process Specification 2.5 Refinement The concept of a refinement is an indirect specification of the behaviour of one protocol machine in terms of the combined behaviour of a set of other protocol machines. A FDT refinement specification specifies the internal structure of a protocol machine. This includes the declaration of new, internal, channel and module types as well as processes 9 and other refinements. Internal refinements, in turn, can have their own internal declarations. The internal structure is defined by three sets of declarations; one for the protocol machine instances (i.e. a module and a process or a refinement), one for protocol machine interconnec-tion (CONNECT) and one for the connections between internal interaction points and those of the enclosing machine being defined (REPLACE). In the sample refinement shown in figure 4 , one sees the internal declaration of a state machine's interaction points (the module player) and transitions (the process player_process). Instances of this machine, P i and P 2 , are declared and then interconnected with the statment Pi.right to PS.left. The refinement's REPLACE section establishes equivalence (a connection) between the interaction points tossin and tossout declared in its associated module team and the internal interaction points PI.left and PS.right. REFINEMENT team_ref(team_num : integer) FOR team; MODULE player; , left : toss(catcher); right: toss(thrower); end player; PROCESS player_process(team_num, player_num : integer) FOR player; (* declaration omited see figure S *) end playerjprocess; (* instances *) PI: player with player_process(team_num, 1); PS: player with playerjprocess(team_num, S); CONNECT Pl.right to PS.left; REPLACE tossin by Pl.left; tossout by PS.right; end teamjref; Figure 4. Example Refinement Specification 10 Chapter 3 The FDT Compiler 3.1 The Compiler The FDT compiler was developed on a VAX-11/750 running Berkeley UNIX 4.2 BSD. The implementation language used was C. Certain sections of the compiler were produced by program generators. The lexical analysis module was generated by the LEX [Lesk 75] utility and the parser was generated by the YACC [John 75] LALR parser generator utility. Both are standardly available in UNLX environments. Not including the automatically generated code, the compiler consists of some 8000 lines of C and approximately 200 modules. It is structured much like all compilers, having the standard lexical analysis, parser and symbol table modules. Processing uses no intermediate forms and is completed in one pass of the source specification. The following section discusses one of the main jobs of the compiler, the translation of PASCAL to C. 3.2 Pascal to C Translation One of the primary issues addressed during the implementation of the compiler was the problem of translating programs and statements written in PASCAL to their equivalent representations in C. Translation between the two languages is almost straight textual sub-stitution, they being very similar in nature having almost identical control constructs and data types. However, enough differences remain to impose limitations on the ease with which the process can be performed. 10 11 Generally, generating a C program from a given PASCAL program does not require sophisticated processing. Begin/ end pairs are replaced by pairs of braces (i.e. { }) and data types like reals translate to floats. All of the control constructs of PASCAL have direct equivalents in C, and some even have the same names (e.g. FOR, WHILE etc.). While it is tempting to think that a text editor is more suited to the job than a powerful compiler. The language differences however preclude this possibility. For example, the two languages have different formats for specifying I/O. PASCAL adopts a style similar to that of FORTRAN or PL/1, while C uses its own considerably different format. Direct translation between the two is difficult but not impossible, but cer-tainly beyond the power of even a sophisticated text substitution system. A simple solution to the problem is to produce one C output statment (i.e. printf) for each field in the PASCAL format list. PASCAL has a different mechanism from C for specifying a return value for a function. PASCAL uses an assignment to the function identifier and C uses a return statement. A solu-tion to this problem is to declare a variable in the corresponding C function to hold the return value and then return it with a return statement. The main difference between the two languages and the hardest one to overcome is their different approaches to defining the scope of identifiers. PASCAL views identifier scope as a variable gradation between being global to the entire program and local to a particular rou-tine. C on the other hand, has only two levels of identifier scope (within one source file), external (global) and internal (local). PASCAL for instance allows function and procedure definitions to be nested while C does not. Implementing a scheme for automatically translat-ing between the two views is not easy. Two solutions to the problem are to use multiple output files for the generated C code or make all identifiers external and systematically rename them to avoid conflicts. Both will 12 work but, particularly in the former case, would be somewhat cumbersome to implement. The solution adopted by this FDT compiler is to simply ignore the problem since the types of programs likely to be processed are unlikely to require extensive use of PASCAL'S scoping rules. This approach does have implications for the user as it prohibits the use of shared identifiers and global data references but should not be too much of a problem. All in all, the problem of translating programs from PASCAL to C is not too difficult provided some restrictions on the types of programs processed can be imposed. Chapter 4 Translating FDT Specifications into C Code 4.1 Overview Generating a high level language program that implements a protocol specified in FDT is not a difficult task. The declarative part of FDT which specifies the protocol machines, their interconnection and the signals they pass, translates into simple conditional expressions, calls to predefined routines and structure (record) declarations. The PASCAL parts of the specification translate directly, requiring relatively little extra processing. The implementation strategy adopted is the same one used successfully by Gerber in his FDT compiler [Gerber 83]. This approach produces two sets of routines from a FDT specification. One set, the transition routines, implements the transition processing of the protocol machines, and the other, the initialization routines, is responsible for constructing a data structure that represents the machines and their interconnections. The transition routines are simply a series of conditional expressions and program blocks. The expressions evaluate the enabling conditions of state transitions and the pro-gram blocks implement the associated operations. The initialization routines use a couple of predefined utilities to construct small parts of the data structure which are then joined to produce the complete representation. The binding force between these two groups of routines is a couple of prewritten driver routines which use the initialization routines to create the necessary data structure and then the transition routines to process the transitions of the protocol machines. The driver rou-tines are an initialization routine (system_init) and a transition scheduler (schedule) which 13 14 directs the processing of signals. 4.2 Data Structure The data structure used to represent the protocol machines and their interconnections consists of a set of linked records. In all, four record structures are used, to store state infor-mation (process block), to represent an interaction point (channel block), to represent a signal and its data fields (signal block) and finally, to store index information for aggregate (array) interaction points (index block). When linked appropriately, records of these four types can represent arbitrarily complex FDT structures in a simple manner. The representation of one protocol machine instance, and the storing of its state infor-mation, is performed by one instance of the process block record type. This record structure has fields for the major state variable (if there is one) and any local variables. It also stores the identifier of, and a pointer to, the instance's transition routine. Process block records also contain links to other process block records and to a list of channel block records representing the protocol machine's interaction points. Each interaction point of a protocol machine instance is represented by a channel block record. Actually a channel block record only represents half of an interaction point, the other half being represented by another channel block record belonging to the protocol machine on the other side of the interaction point. The channel blocks representing the interaction ponts of a particular machine instance are joined together to form a linked list attached to the pro-cess block of that instance. Each channel block record stores two numbers to identify it, the first is the number of the interaction point and the second is the index of the channel block record for an aggregate interaction point. In addition, each record also contains pointers to the channel and process blocks on the other side of the communication path. These pointers constitute the actual 15 connection between two protocol machines. The queue of signals which can exist at an interaction point is represented by a list of signal block records attached to a channel block record. Signal block record instances represent messages sent by a protocol machines. They contain fields to store an identifying number and optional transmitted data. Instances are not produced by the initialization routines but come from the execution of OUT statements in transition routines. Finally, those channel records belonging to aggregate interaction points store their index specified in the FDT source via a list of index block records. The index number stored in the channel record is the ordinal of the interaction point in a row-major ordering of the array. Index block records simply contain a single number that is the value of one dimension of an array. These values are required by the enabling conditions of transitions to identify, and possibly test, the identity of an interaction point receiving a signal. 4.3 Initialization Routines The set of initialization routines contains two types, those that generate a representa-tion of a machine instance (i.e. a process block and its channel list) and those that combine the machine representations into larger structures. Each process specification in the FDT source produces one routine belonging to the first group, and each refinement specification produces one belonging to the second. Both groups make use of a series of prewritten utilities to perform their functions. The process initialization routines are quite simple. Their only responsibility is to con-struct the part of the data structure needed to represent one machine instance. They merely allocate a process block record, attach a list of channel block records, perform any initializa-tion specified in the FDT source, and then add the process block record to a linked list. 16 The refinement initialization routines are a bit more complex as they must create a complete representation of the structures defined within them. Their task is simplified some-what by the use of initialization routines from both groups to construct the machine instance representations. Their main job then becomes the combining of these small sections into one larger one representing the internal structure. The operations performed by a refinement initialization routine can be divided into four phases, three of which correspond to the instance, connection and replacement sections of a FDT refinement and the fourth to what could be termed a "clean up" phase. The instance section of a refinement defines the number and type of protocol machines in the internal structure. Each instance specification causes a call to the appropriate process or refinement routine to be generated, this call will simply add another machine instance on to a linked list. The connection section of a refinement specifies which interaction points of the protocol machine instances are joined together. Each interconnection generates one call to a prewrit-ten utility called connect_ports which does the actual pointer manipulation to form the con-nection. The replacement section of a refinement specifies which internal interaction points are to be used for the external interaction points of the protocol machine being defined. The corresponding code in the refinement initialization routine first generates what is termed a "refinement header", consisting of a process block record and a channel block record list, and which represents the external protocol machine and its interaction points. The list of process block records produced by the instance and connection phases and which is now termed the "refinement body" is linked to the refinement header. Each replacement specification in the FDT source generates a call to a prewritten utility replace_port3 which makes connections between the channel block records in the refinement header and those in the refinement 17 body. The refinement header is really a place holder whose purpose is to mimic a process block and channel list produced by a process initialization routine. This uniformity in representa-tion allows protocol machine instances from both process and refinement initialization rou-tines to appear to be identical in the process block record list processed by the connection and replacement phases of a refinement initialization routine. This allows a consistent numbering scheme to be employed when specifying interconnections. The prewritten utilities connect_ports and replace_ports are smart enough to recognize connections to refinement headers and will make the actual connections to internal channel block records in the refinement bodies attached to the headers. The fourth phase of a refinement routine, the "clean up" phase, is where the refinement headers holding the place of a protocol machine representation in the refinement body are removed and replaced by their refinement bodies. This task is performed by the prewritten utility clean_up. 4.4 Transition Routines The actual implementation of a specified protocol, as opposed to simply creating a data structure, is achieved by a section of the generated code known as the transition routines. These routines, together with the prewritten transition scheduler, completely embody the behaviour of the model described in the FDT source. The transition scheduler calls a transition routine whenever it decides that some pro-cessing should occur. The transition routine receives from the scheduler a process block record and possibly channel and signal block records. The process block record contains the state information of the machine instance needed to correctly process the state transitions. If the transition routine does receive channel and signal block records then the associated proto-18 col machine has received a signal at an interaction point (the one represented by the channel block record), if the signal does not cause a transition it is simply requeued. If the routine does not receive the records then the scheduler has decided that a spontaneous transition should be attempted by the transition routine. For their part the transition routines consist of a series of if statments, each of which corresponds to one transition in the FDT source. The boolean expression in the statement evaluates the truth value of the enabling condition and the body contains the associated action. Chapter 5 Illustrative Implementation Examples This chapter presents two protocols and describes their implementation. The first pro-tocol is a simple one invented to illustrate the implementation process. The second is the alternating bit protocol. 5.1 Example 1—The Hot Potato Protocol The simple protocol described below is an excellent vehicle for illustrating the imple-mentation process used by the compiler. This protocol models a system of two "teams" of two "players" which continuously pass a message (a hot potato) around in a circle. Its specification contains a good sampling of the features of contained in FDT. In addition to the standard specification of channels, modules, processes and refinements, it contains composite protocol machine definitions and argument passing to processes and refinements. The actions of each "player" in the protocol are identical and specified by one process. When a player receives a "potato" message from the player on his left he prints a message identifying himself and the player who sent the message. He then sends a "thankyou" mes-sage to that player and a new potato message to the player on his right. The teams are organized identically and specified by a single refinement. The players are conceptually side-by-side, with the right of one being connected to the left of the other. The teams are joined by connecting the two remaining sides of the players on one team to their opposite numbers on the other. Figure 5 shows the interconnection of the protocol machines involved. As part of his local state information each player stores two numbers, one identifies his 19 team and the other is his player number within the team. The complete FDT specification for the protocol is shown in Figures 6 and 7 below. Player 1 l e f t tossin tossout right l e f t Player 2 right tossout tossxn right Player 2 l e f t l e f t right Player 1 Team 1 Team 2 Figure 5. Illustration of Hot Potato Protocol Machines 21 MODULE hot_potato; end hotjpotato; REFINEMENT hot_ref FOR hot_potato; CHANNEL toss (thrower, catcher); by thrower: potato (throwerjteam, thrower_num : integer); by catcher: thanks; end toss; MODULE team; tossin : toss(catcher); tossout: toss(thrower); end team; REFINEMENT team_ref(team_num : integer) FOR team; MODULE player; left : toss(catcher); right: toss(thrower); end player; PROCESS player_process(team_num, player_num : integer) FOR player; (* see Figure 7 for definition *) end playerjprocess; PI: player with player_process(team_num, 1); PS: player with player_process(team_num, S); CONNECT PI.right to PS.left; REPLACE tossin by PI.left; tossout by PS.right; end team_ref; Tl: team with team_rtf(l); TS: team with team_ref(2); CONNECT Tl.tossout to TS.tos8in; TS.tossout to Tl.tossin; end hot_ref; Figure 6. FDT Specification of Hot Potato Protocol 22 PROCESS playerjprocess(team_num, player_num : integer) FOR player; QUEUED left, right; (* queuing status *) VAR (* local variable declarations *) the_team, thejplayer : integer; INITIALIZE (* local variable initiallization *) begin thejteam := teamjnum; thejplayer := player_num; end; TRANS (* potato message on left *) WHEN left.potato begin writeln('Player ',thejplayer,' of team ', thejteam,' caught a potato from player \ thrower_num, ' of team \thrower_team); OUT right.potato(the_team, the_player); OUT left.thanks; end; TRANS (* thanks message on right *) WHEN right.thanks begin writelnf Player ', the_player,' of team ', thejeam,' got a thankyou'); end; TRANS (* spontaneous *) provided ((the_player = 1) and (thejeam = 1)) begin OUT right, potatofthejeam, the jplayer); end; end playerjprocess; Figure 7. FDT Specification of Player Process The overall structure of the system is contained by the top level refinement hotjref which is specified for the empty, top level, module hotjpotato. This refinement, directly or indirectly, contains all of the other declarations. The system structure is defined by the instance and connection specifications at the end of hotjref. 23 The refinement team_ref is similar to hot_ref except that it also has a replace specification which defines which interaction points, internal to team_ref, are to be used for the interaction points tossin and tossout of the refinement's module team. Note that hotjref does not have a replace specification as its module hotjpotato does not define any interaction points. In the instance specifications, both refinements pass arguments to the refinement or process used. In hotjref one number identifying the team of the instance is given to the refinement leamjref, which passes it and a player number to the process playerjprocess in its instance specification. Playerjprocess stores the numbers it receives as part of the local state information of each machine instance. The actions of the players in the protocol are specified by playerjprocess. It declares that the two interaction points, left and right, of its module player are to queue their signals, that the protocol machine has two local variables, thejteam and the_player, and that they are to be initiallized to the values of the two parameters passed. The first transition of playerjprocess occurs whenever a potato message arrives via the left interaction point. It prints a message and transmits two more messages. The second transition occurs whenever a thanks message arrives via the right interac-tion point of the protocol machine, it also prints a message. The third transition will only occur for player one of team one when the transition scheduler detects that there are no messages enqueued and awaiting processing. For this pro-tocol that only occurs a the start of processing. 5.1.1 Implementation Code The implementation code produced by the compiler is placed into one output file. The 24 first entries in this file are a series of "#include's" whose purpose is to direct the C compiler to include files like the C standard input/output library (stdio.h). The next entries are the signal and process block declarations and then various initiallization, transition and user defined procedures which are in no particular order. The finally entry of the file is another "#include" which directs the C compiler to include (compile) the prewritten utility routines. The output file generated for the example in Figures 6 and 7 is shown in Figure 8. The bodies of the procedures have been deleted for brevity and are show individually in later Fig-ures. 25 #include <stdio.h> ^include <stringa.h> ^include "listdefs.hT struct signal_block { int signaljd; struct signaljblock *next; union { struct { struct { int thrower_team, throwerjnum; } potato; } toss; } Ivars; }; struct processjblock { struct proces8_block *next; char p_ident[MAXJDENT_LENGTH+lj; struct channeljblock *chan_list; struct proce88_block *refinement; int (*proc_ptr)(); union { struct { int thejttam, thejplayer; } 8_playerjprocess; } Ivars; }; struct processjblock *iohot_ref(p_block) struct processjblock *ioteam_ref(p_block, team_num) struct processjblock *ioplayer_j>rocess(processJist, teamjnum, player_num) player_process() #include "fdtutil.c" Figure 8. Implementation Code for Hot Potato Protocol The signal block declaration contains two fields, throwerJeam and thrower_num, which store the data values of a potato message. If there had been other channel declarations, at any level of nesting containing messages with data fields, they to would have appeared in the declaration. The process_block declaration has similar fields for the storage of variables for a proto-26 col machine instance. It also contains the identifier and a procedure pointer to the transition routine associated with the process_bk>ck instance. The initiallization and transition routines follow the two structure declarations. They use the same identifiers as their associated refinement or process in the the FDT source, with the exception that the initiallization routines also have a "io" prefix. This prefix is necessary to distinguish between the two routines, one initiallization and one transition, generated for each process specification. The initiallization routine generated for the refinement kot_ref is iohot_ref and is shown in Figure 9. This procedure is called by the system initiallization utility to generate the entire representation data structure. struct processjblock *iohot_ref(p_block) struct process_block *p_block; { struct proces8_block *ioteam_ref(); struct processjblock *ioteam_ref(); struct channeljblock *add_channel_block(), *c_ptr; struct processjblock *add_refinement_header(), *clean_up(), *processJist; processJist = NULL; processjist = ioteam_ref(processJist, 1); process Jist = ioteam_ref(processJist, 2); connect_ports(proces8jist, 2, 2, 0, 1, 1, 0); connect_ports(processJist, 1, 2, 0, 2, 1, 0); pjblock = add_refinement_header(pJblock, processjist); p_block-> refinement = clean_up(p_block-> refinement); return(pjblock); } Figure 9. Initiallization Routine for hot_ref The initiallization routine generated for the refinement teamjref is shown in Figure 10. It is slightly more complex than iohot_ref as it must also add channel blocks to its refinement 27 header (add_channel_block) and establish connections between them and internal interaction points (replace_ports). The calls to connectjports in Figures 9 and 10 contain a cryptic set of numbers as arguments to the routine. These numbers describe which two channel blocks are to be inter-connected to form the interaction point. For example, the set of three numbers 2, 2, 0, tells connect_ports to look in the channel list of the second process block in the process list for a channel block containing the two numbers 2 and 0. Calls to replace_ports contain similar sets of numbers except that the process block number for the first channel block is not required because the channel list is know to be in the refinement header and so is omitted. Note that the numbering of the process blocks in the list is the reverse of their creation since the initiallization routines place them at the front of the process block list. struct processjblock *ioteam_ref(p_block, team_num) struct processjblock *p_block; int team_num; { struct processjblock Hoplayer_process(); struct processjolock *ioplayer_process(); struct channeljblock *add_channel_block(), *c_ptr; struct processjblock *add_refinement_header(), *clean_up(), *processJist; processJist — NULL; processJist=ioplayerjprocess(processJist, team_num, 1); processjist=ioplayer_process(processjist, team_num, 2); connect_ports(processJist, 2, 2, 0, 1, 1, 0); pjblock = add_refinement_header(pJblock, processjist); pJolock-> chanJist=add_channel_block(p_block-> chanjist, &c_ptr, FALSE, 1, 0); p_block-> chanjist—add_channel_block(p_block-> chanjist, &c_ptr, FALSE, 2, 0); replace_port(p_block, 1, 0, 2, 1, 0); replace_port(p_block, 2, 0, 1, 2, 0); p_block-> refinement = clean_up(p_block-> refinement); return(pjblock); } Figure 10 . In i t ia l i za t ion Routine for team_ref 28 The two declarations of ioplayerjprocess in Figures 9 and 10 is not an error, simply a harmless idiosyncrasy of the compiler which was left in to ease the implementation of the compiler. The C compiler will not complain about multiple function definitions so long as they are consistent. The initiallization routine generated for the process playerjprocess is shown in Figure 11 and the transition routine in figure 12. struct processjblock *ioplayerjprocess(process_list, teamjnum, playerjnum) struct processjblock *processJist; int teamjnum, playerjnum; { struct processjblock *p_block, *add_process_block(); extern int playerjprocessQ; struct channeljblock *add_channel_block(), *cjptr; pjblock — addjprocess_block(proces8_list, player jprocess," playerjprocess" ); p_block-> chan_list = add_channel_block(p_block-> chanjist, &cjptr, TRUE, 1, 0); p_block-> chan_list = add_channel_block(p_block-> chanjist, &cjptr, TRUE, 2, 0); p_block->lvars.sjplayerjprocess.thejeam — teamjnum; pJlock->lvars.sjplayer_process.thejplayer = playerjnum; return(pjblock); } Figure 11. Initiallization Routine for player_process player_process(p_block, channel, signal) struct proces8_block *p_bloch; struct channeljblock *channel; struct signaljlock *signal; { struct signaljolock *s_ptr; if ((channel != NULL) ) if ((channel-> cjd == 1) && (signal->signalJd == 0)) {{{ printff"Player "); printf("%am ,p_block-> Ivars.s_player_process.thejplayer); printff" of team "); printf("%am ,p_block-> Ivars.s_player_process.theJeam); printff" caught a potato from player "); printff "% a™ ,signal-> Ivars. toss, potato, throw er_num); printff" of team "); printff "% a" ,signal-> Ivars.toss.potato, throwerJeam); printf("0); . s_ptr = ALLOCATE(signalJolock); s_ptr-> signal Jd = 0; s_ptr-> Ivors, toss, potato, throwerjeam = p_block-> Ivars.sjplayer_process.the Jeam; s_ptr-> Ivars.toss.potato.thrower_num = p_block-> Ivars.s_playerjprocess.the _player; out(p_block-> chanjist, s_ptr, 2, 0); 8_ptr = ALLOCATE(signal_block); s_ptr-> signal Jd = 1; out(p_block-> chanjist, s_ptr, 1, 0); } goto dispose; }} if ((channel != NULL) ) if ((channel-> cjd ==2) && (signal-> signal Jd =— 1)) {{{ printff "Player "); printff"%cT ,pJlock-> Ivars. s_playerjprocess.the_player); printff" of team "); printff "%(T ,p_block-> Ivars.sjplayer_process.theJeam); printff" got a thankyou"); printff "0);' } goto dispose; }} if (channel != NULL) { requeuefchannel, signal); signal = NULL;} if ff((fpJlock->lvars.s_player_process.thejplayer == 1)) && (fpJlock-> Ivars.sjplayerjprocess.the Jeam == 1))))) {{ sjptr = ALLOCATE(signalJlock); s_ptr-> signal Jd = 0; 8jptr-> tvars.toss.potato. throwerJeam = p_block->lvars.sjplayerjprocess.the Jeam; sjptr-> Ivars. toss, potato, throwerjnum = p_block->lvar8.sjplayerjprocess.thejplayer; outfp_block->chanjist, sjptr, 2, 0); } goto dispose; } dispose: freefsignal); } Figure 12. Transition Routine for player_process 30 5.1.2 Execution Description The creation of the data structure that represents the interconnected protocol machines that implement the hot_potato protocol is initiated by a call to the initiallization routine iohot_ref by the prewritten utility 8ystem_init. The subsequent sequence of calls to the other initiallization routines and the construction of the data structure are described below. The first operation performed by iohotjref is to call the routine ioteam_ref, which, in turn, calls the initiallization routine ioplayerjprocess twice to create two protocol machine instances. The structure returned by one of these calls is shown in part (a) of Figure 13. Ioteamjref then calls connectjports to connect together the interaction points of the two instances. The resulting structure is a refinement body and is shown in part (b) of Figure 13. Next, ioteamjref creates a refinement header (addjrefinementjheader), attaches the refinement body and calls replacejports to make interconnections between the header and the body. Its job is then completed by calling the prewritten utility clean jap which in this case has no work to do and then returning. The complete structure returned by ioteamjref is shown in part (c) of Figure 13. Iohotjref now receives control and proceeds to call ioteamjref a second time to gen-erate another machine representation. That structure is shown in part (d) of Figure 13. With the construction of the two instances now complete iohotjref calls connect_ports to interconnect them. Connect jports will detect that it is making connections between refinement headers and will connect to the appropriate channel blocks in their refinement bodies instead. Iohotjref then creates a refinement header (without channel blocks) for the refinement body (i.e. the two structures returned by ioteamjref ). 31 The last operation of ioholjref is to call the utility cleanjup which replaces the refinement headers, in its refinement body, with their bodies. The complete structure returned to system_ir.it is shown in part (e) of Figure 13. VMS 1 0 % -T 8-] 2 JO Iffi# ff| SS Iff (a) (b) 1 o k ~ 2 1 1 1 sr I ^ 2 0 -8'r9' .0 r 1-4 T \t±_ IT -01 # 2 o iff -e ff 1 o|ff 1 ' 1 •8- T 1 0 •8" 1 ff QL9- | (c) Figure 13. Representation Data Structures for Hot Potato Protocol 32 VflHJ 1 0 0 J3T & sr 2 Z $ Iff 44 1 0 1 0 -€T[ — & f 1 T o ^ 2 Op? 13* 1 0 ar St er 2 0 J9r i J0-1 o # a T T #1 r I -Figure 13. Representation Data Structures for Hot Potato Protocol (continued) 33 2 0 -rr -8" • i 0 -e- 2 o le-& 0 Cel Figure 13. Representation Data Structures for Hot Potato Protocol (continued) 34 5.1.3 Transition Processing When the initiallization routines have completed their task and built the representation data structure the transition scheduler receives control. The scheduler distributes enqueued messages and spontaneous transitions in a round robin manner. The identities of the spontaneous routines are hand coded into the scheduler by the user (not everything is automatic!). The user enters a series of string comparisons between the identifier stored in the process_block instances and the identifiers of the spontaneous transi-tion routines. These tests are OR'ed together and become the boolean expression of an if statement that decides whether to call the transition routine to attempt a spontaneous transi-tion. In this example, when the scheduler first receives control it tests for the existence of enqueued signals. Discovering that none exist it proceeds to search the process block list for a process block that contains a transition routine identifier matching one of those known (hand coded) to contain a spontaneous transition. The first block tested just happens to contain (like the others) such an identifier (player_proces8) so the scheduler calls that routine. Once a signal does get enqueued by the spontaneous transition of the protocol machine of player one, team one, the scheduler stops searching for a spontaneous transition and goes about the job of dispatching signals. 5.2 Example 2—The Alternating Bit Protocol The second example is an implementation of the alternating bit protocol which serves to illustrate the ability of the compiler to implement a real protocol. The specification of the protocol is taken from the ISO working document [ISO 84] and is shown in Appendix TV. 35 The specification contains one, top level, refinement ab_ref, and five module types ab_pc, Alternating_Bit, timer, network and user. It also has four different channel types and various messages. The specification models the typical situation of a protocol machine on a particular level of abstraction. It has the alternating bit protocol machine and a system entity (timer) on one level, as well as entities on the levels above (user) and below (network). This specification was used to create a communication path between two separate hosts. This required the modification of the system initialization routine system_init, the system scheduler schedule and the the two signal transmission routines get_signal and out. A time out facility was also implemented. Code for these routines is given in Appendix V. The system initialization routine was modified to allow it to establish a network connec-tion between the two hosts being used. The actual communication path was created using a set of locally developed network primitives which allow easy access to a local area network (ETHERNET). The system scheduler was modified so that it tested the result of a call to get_signal before it called the destination routine. Get_signal was modified to detect when it was at the particular channel through which signals from the network are to arrive. When at the designated channel it called a non-blocking network receive primitive in attempt to get a signal from the other host. The routine out was modified to detect the transmission of a signal over the channel designated to carry traffic to the other host. Instead of queueing the signal it places it in a buffer and calls a network send primitive. The time out facility was provided by a pair of C routines which schedule and test timers. These two routines are quite simple. The time out scheduler, schedulejtimeout, adds the timer duration to the present time and stores the value. The routine timer_expired checks to see if the system time is later than the stored time and returns the appropriate truth value. The implementation code generated for this example can be found in Appendix Chapter 6 Conclusion 0.1 Thesis Summary The development of formal models for protocol specification has opened the door to the possibility of automatically generating protocol implementations directly from their specification. The wide spread availability of implementation tools will allow protocol imple-mentors to produce compatible protocol implementations with ease. The compiler developed demonstrates the feasibility of producing such a tool. It generates virtually all of the code needed to implement a protocol (the only thing it does not produce are some simple declara-tions and tests in two utility routines). And both it and its output code are written in highly portable C. Despite of its large size, 8000 lines, it runs very quickly, processing the two examples in negligible time (less than a second). The restrictions placed on the structure of the PASCAL programs accepted by the com-piler, namely the elimination of nested routines and global references, could be a factor when more complex protocols are to be processed. However, at present the restrictions do not appear to be too severe. The success of the venture can be measured by contrasting automatic and manual pro-tocol implementation techniques. The compiler produces consistently well structured and easy to understand code. The quality of manually generated code varies considerably. Com-piler generated code is easy to maintain and modify, a change in the input specification is all that is required. On the other hand, manually produced code requires a great deal of effort and expense to maintain. Perhaps the greatest difference between the two implementation methods is the respective confidence given to their generated implementations. Code pro-duced by a compiler can generally be assumed to be a correct representation of the 37 38 specification, whereas manually produced code cannot. 6.2 Enhancements Further testing of the compiler on real-life protocols such as the ISO transport protocol is desirable. Such a test would further demonstrate the usefulness of using such tools and perhaps spawn the development of production versions of the compiler. Enhancements to the compiler itself can also be made. The processing of the scope of transition enabling condition clauses is currently handled clumsily and as a result the useful-ness of some of the shorthand clause specifications is restricted. PASCAL set types, were not implemented as they were not considered to be important enough to warrant the effort. The FDT DELAY clause which implements timer functions was not implemented as timers can be simulated with system calls. Adding the DELAY clause would enhance the compatibility of the compiler with the ISO standard. A major enhancement to the system would be the implementation of protocol machines as separate processes running under control of the host's operating system. This approach would be a closer representation of the model of independent protocol machines then the current one. References [Aho 78] Aho, A., Ullman, J., "Principles of Compiler Design", Addison-Wesly Publishing Com-pany, 1978. [Blum 81] Blumer, T. P., Tenney, R. L. , "An Automated Formal Specification Technique for Pro-tocols", Proceedings INWG/NPL workshop, May 1981, pp. 277-326. [Boch 80] Bochmann, B. V., Sunshine, C. A., "Formal Methods in Communication Protocol Design", IEEE Transacations on Communications, Vol. Com-28, No. 4, April 1980, pp. 624-631. [Dant 80] Danthine, A. A. S. , "Protocol Representation with Finite-State Models", IEEE Trans. Commun. vol. COM-28, pp. 632-643, April 1980. [Gerber 83] Gerber, G. W. , "Une Methode D'Implantation Automatisee de Systemes Specifies For-mellement", Publication #142, Departement DTnformatique et de Recherche Operationnelle, Universite' de Montre'al, Aout 1983. [Hansson 84] Hansson, H., "Aspie, A system for Automatic Implementation of Communication Proto-cols", Uptec 8486R, Uppsala Institute of Technology, Uppsala 1984. 39 40 [ISO 84] "A Formal Description Technique based on an extended state transition mo der, ISO/TC 97/SC 16/WG 1 Subgroup B, Working document, March 1984. [Jensen 74] Jensen, K., Wirth, N., "Pascal—User Manual and Report", Lecture Notes in Computer Science no. 18, Springer-Verlag. 1974. [John 75] Johnson, S. C , "Yacc: Yet Another Compiler-Compiler", Comp. Sci. Tech. Rep. No. 32, Bell Labratories, Murray Hill, New Jersy 1975 [Kern 78] Kernighan, B. W., Ritchie, D. M. , "The C Programming Language", Prentence-Hall, 1978. [Lesk 75] Lesk, M. E . , "Lex—A lexical Analyzer Generator", Comp. Sci. Tech. Rep. No. 39, Bell Labratories, Murray Hill, New Jersy (October 1975) [Sunsh 79] Sunshine, C. A. , "Formal Techniques for Protocol Specification and Verification", Computer, vol. 12, pp. 20-27, Sept. 1979. [Tanen 81] T A N E N B A U M , A. S. , "Computer Networks", Prentence-Hall, 1981. Appendix I FDT Grammar specification -> seqsect seqsect -> section ";" seqsect | /* empty */ section -> channel | module | process | refinemt channel -> constd typed "channel" IDENT "(" rolelist ")" ";" byclause "end" IDENT rolelist -> IDENT seqident seqident -> "," rolelist | /* empty */ byclause -> "by" rolelist ":" signal byclause | /* empty */ signal -> IDENT signalpara ";" signal | /* empty */ signalpara -> "(" paradef ")" | /* empty */ seqparadef -> ";" paradef | /* empty */ paradef -> rolelist ":" basictype seqparadef module -> "module" IDENT ";" portlist "end" IDENT portlist -> rolelist ":" array IDENT "(" IDENT ")" ";" portlist | /* empty */ 41 array -> "array" "{" indextype seqindext "}" "oP | / * empty * / indextype -> simpletype seqindext -> "," indextype seqindext | / * empty * / refinemt -> "refinement" IDENT signalpara "for" IDENT " refbody "end" IDENT refbody -> seqsect instance connect replace | / * empty * / instance -> rolelist ":" IDENT "with" IDENT actualpar ";" seqinst seqinst -> instance | / * empty * / connect -> "connect" intconn | / * empty * / intconn -> mport "to" mport ";" seqintconn seqintconn -> intconn | / * empty * / replace -> "replace" extconn | / * empty * / extconn -> port "by" mport ";" seqextconn seqextconn -> extconn | / * empty * / port -> IDENT optindex optindex -> "{" constant listconst "}" | / * empty * / mport -> IDENT "." port 43 process -> "process" IDENT signalpara "for" IDENT ";" proc body "end" IDENT qchannel -> "queued" rolelist ";" | / * empty * / procbody -> qchannel constd typed pvard procfuncd init trans | / * empty * / pvard -> "var" procvar | / * empty * / procvar -> IDENT ":" "(" rolelist ")" ";" seqvardecl | vardecl stateset -> IDENT | / * empty */ init -> "initialize" stateset "begin" initstatmt seqstatmt "end" ";" | / * empty * / initstatmt -> plainstatmt trans -> "trans" seqclause opttrans opttrans -> trans | / * empty */ seqclause -> clause seqclause | opttag block ";" seqtrans clause -> "any" paradef "do" | "when" IDENT vparam "." IDENT | "from" rolelist | "to" nextmstate | "provided" expression | "priority" idorint seqtrans -> seqclause | / * empty * / opttag -> IDENT ":" j / * empty * / vparam -> "{" rolelist "}" | / * empty */ listvariable-> "," variable | /* empty */ nextmstate-> IDENT | "same" idorint -> IDENT | INTEGER block -> labeld constd typed vard procfuncd "begin" statmt seqstatmt "end" labeld -> "label" INTEGER seqinteger ";" | /* empty */ seqinteger -> "," INTEGER seqinteger | /* empty */ constd -> "const" defconst | /* empty */ defconst -> IDENT "=" constant ";" seqdefconst seqdefconst-> defconst | /* empty */ constant -> optsign numconst | STRING optsign -> SIGN | /* empty */ numconst -> INTEGER | REAL | IDENT typed -> "type" deftype | /* empty */ deftype -> IDENT "=" type ";" seqdeftype seqdeftype -> deftype | /* empty */ type -> simpletype | optpack typstruct | "*" IDENT | "'" "boolean" | "char" | "integer" I "'" "real" simpletype -> "(" rolelist ")" | SIGN numconst constant | INTEGER constant | IDENT optconst | "boolean" | "char" | "integer" | "real" optconst -> ".'." constant | / * empty * / optpack -> "packed" | / * empty */ typstruct -> "array" "{" simpletype seqsimplet "}" "oF type | "record" field "end" seqsimplet -> "," simpletype seqsimplet | / * empty * / field -> fixedpart seqfield | "case" IDENT typselect "oF variant fixedpart -> rolelist ":" type | / * empty */ seqfield -> ";" field | / * empty * / typselect -> ":" basictype | / * empty */ variant -> constant listconst ":" "(" field ")" seqvariant | / * empty * / seqvariant -> ";" variant | / * empty * / listconst -> "," constant listconst | / * empty * / vard -> "var" vardecl | / * empty * / vardecl -> rolelist ":" type ";" seqvardecl seqvardecl -> vardecl | / * empty * / procfuncd -> procefuncd pfheader ";" pfbody ";" | /* empty */ pfheader -> "procedure" IDENT lpara | "predicate" IDENT lpa | "function" IDENT lpara ":" basictype pfbody -> block | "extern" | "forward" | "primitive" lpara -> "(" spara seqspara ")" | /* empty */ seqspara -> ";" spara seqspara | •/* empty */ spara -> rolelist ":" basictype | "var" rolelist ":" basictype factor -> REAL | STRING | "nil" | INTEGER | "{" seqsetint "}" | "(" expression ")" | "not" factor | IDENT seqfactid seqfactid -> lseqvaria | "(" index ")" index -> expression seqindex seqindex -> "," index | /* empty */ lseqvaria ->"{" index "}" lseqvaria | "." IDENT lseqvaria | " A" lseqvaria | /* empty */ seqsetint -> setint lseqset | /* empty */ lseqset -> "," setint lseqset | /* empty */ setint -> expression seqxpset seqxpset -> ".." expression | /* empty */ 47 term -> term OPERMULT factor | factor simplexp -> simplexp OPERADD term | optsign term expression -> simplexp OPEREL simplexp | simplexp statmt -> INTEGER ":" plainstatmt | plainstatmt plainstatmt -> IDENT appendix | "out" IDENT seqindice "." IDENT actualpar | "goto" INTEGER | "begin" statmt seqstatmt "end" | "if" expression "then" statmt else | "case" expression "of" case seqcase otherw "end" | "repeat" statmt seqstatmt "until" expression | "while" expression "do" statmt | "for" IDENT ":=" expression direction expression "do" statmt | "write" iolist | "writeln" lniolist | /* empty */ actualpar -> "(" index ")" | /* empty */ newmstate -> IDENT | "same" seqstatmt ->";" statmt seqstatmt | /* empty */ else -> "else" statmt | /* empty */ seqcase -> ";" case seqcase | /* empty */ case -> constant listconst ":" statmt | /* empty */ 48 otherw -> "otherwise" statmt seqstatmt | /* empty */ lniolist -> ioiist | /* empty */ iolist -> "(" ioexp "): loexp -> ioident seqioident seqioident -> "," ioexp | /* empty */ ioident -> expression ioextra ioextra -> ":" simplexp | /* empty */ direction -> "to" | "downto" variable -> IDENT Iseqvaria listvariable appendix -> actualpar | Iseqvaria ":=" expression seqindice -> "{" index "}" seqindice | /* empty */ basictype -> IDENT | "boolean" | "char" | "integer" | "real" APPENDIX H Utility Routine Listings int signal_pending; /. */ struct processjblock *add_processJblock(processJist,proc_ptr,identifier) This function allocates a new process block, initializes it, and places it at the head of the process list passed to it. The pointer to the process_list is returned. •/ struct processjblock *processJist; int (*proc_ptr)(); char identifier; { struct processJ>l°ck *ptr, *temp_ptr; ptr = ALLOCATE( process_block); ptr->next = processjist; ptr->proc_ptr =proc_ptr; strcpy(ptr->pjdent,identifier); ptr->chanjist = NULL; ptr-> refinement = N U L L ; return(ptr); } /* */ struct channel Jalock *add_channelj3lock(channelJist,c_ptr,queued_flag, 49 number,index) /* This function allocates a new channel block, initializes it, and places it at the end of the channel list passed to it. It returns the channel list. •/ struct channel_bk>ck *channel_list, *(*c_ptr); int queued_flag,number,index; { struct channel_block *ptr, *temp_ptr; / * make a new channel block * / ptr = ALLOCATE( channel_block); ptr->next = NULL; ptr->c_id = number; ptr->index_num = index; ptr->signal_list = NULL; ptr->queued =queued_flag; ptr->target_proc = NULL; ptr->target_channel= NULL; ptr->index_list = NULL; *c_ptr = ptr; if (channeljist != NULL) { / * find the end of the channel list * / for (temp_ptr = channel_list; temp_ptr->next != NULL; temp_ptr = temp_ptr->next); temp_ptr->next = ptr; retum(channel_list); } else return(ptr); } /. */ struct channel_block *find_channel(channel_list,id,index) This function returns a pointer to the first channel block with the passed id in the channel list. */ struct channel_block *channel_list; int id, index; { struct channel_block *ptr; / * find the block * / for (ptr = channel_list; (ptr->c_id != id)||(ptr->index_num != index); ptr = ptr-> next); return(ptr); } struct process^lock *add_refinement_header(process_list,ref_body) / * This function allocates a "refinement" type process header and places it at the head of the process list. The ref_body (also a process list) is then attached to the refinement header. */ struct process_block *process_list, *ref\body; { struct process_bl°ck *ptr,*add_process_block(); ptr = add_process_bi° ck(P' ,ocess_list,NULL,"reflnement"); ptr->refinement= ref_body; return(ptr); } connect_ports(process_list, instance_numl, channel_numl,indexl, instance_num2, channel_num2,index2) /* This routine interconnects the specified channels. • / struct process^l 0 0^ *process_list; int instance_numl, instance_num2, channel_numl, channel_num2, indexl, index2; { struct process_block *find_process(), *p_ptrl, *p_ptr2; struct channel_block *find_channel(), *c_ptrl, *c_ptr2; p_ptrl p_ptr2 c_ptrl c_ptr2 find_process(process_list,instance_numl); find_process(process_list,instance_num2); find_channel(p_ptrl->chan_list,channel_numl, indexl); find_channel(p_ptr2->chan_list,channel_num2, index2); If the channel blocks are already connected to another channel block then they must be in the header of a refinement so take their targets as the channel blocks to connect to. */ p_ptrl p_ptr2 c_ptrl c_ptr2 = (c_ptrl->target_proc = = NULL) f p_ptrl : c_ptrl->target_proc; = (c_ptr2->target_proc = = NULL) ? p_ptr2 : c_ptr2->target_proc; = (c_ptrl->target_channel = = NULL) ? c_ptrl : c_ptrl->target_channel; = (c_ptr2->target_channel = = NULL) ? c_ptr2 : c_ptr2->target_channel; / * make the connection */ c_ptrl->target_proc = p_ptr2; c_ptrl->target_channel = c_ptr2; c_ptr2->target_proc = p_ptrl; c_ptr2->target_channel = c_ptrl; } struct process_block *find_process(process_Iist, number) This function returns a pointer to the number'th element of the process list. struct process_bl° ck *process_list; int number; int i; for (i = 1; i < number; i++) process_list = process_list->next; return(process_list); } replace_port(ref_ptr, port_num, port_index, instance, channel_num,index) / * This routine connects a port (channel) in a refinement header to a port in the refinement body. */ struct process_block int { *ref_ptr; port_num, port_index, instance, channel_num, index; struct process_block struct channel block *p_ptr,*find_process(); *c_ptrl,*c_ptr2,*find_channel(); p_ptr = find_process(ref_ptr-> refinement, instance); c_ptrl = find_channel(ref_ptr->chan_list, port_num,port_index); c_ptr2 = find_channel(p_ptr->chan_list,channel_num,index); p_ptr = (c_ptr2->target_proc = = NLILL) ? p_ptr : c_ptr2->target_proc; c_ptr2 = (c_ptr2->target_channel = = NULL) ? c_ptr2 : c_ptr2->target_channel; cjptrl->target_proc = p_ptr; c_ptrl->target_channel — c_ptr2; c_ptr2->target_proc = ref_ptr; c_ptr2->target_channel = c_ptrl; } struct process_block *clean_up(process_list) / * This function removes the refinement header in a process list. It returns a process list which is a concatenation of the refinement bodies •/ struct process^lock *process_list; { struct process_block *ptrl, *ptr2, *remove_header(); if (processjist = = NULL) { return(NULL); } else { ptrl = process_list->next; ptr2 = process_list; if (strcmp(process_list->p_ident,"refinement") = = 0) { process_list = remove_header(process_list); for (ptr2 = process_list; ptr2->next != NULL; ptr2 = ptr2->next); ptr2->next = ptrl; } while (ptrl != NULL) { if (strcmp(ptrl->p_ident,"refinement") = = 0) { ptrl = ptrl->next; ptr2->next = removeJieader(ptr2->next); while (ptr2->next != NULL) { ptr2 = ptr2->next; } ptr2->next = ptrl; } else { ptr2 = ptrl; ptrl = ptrl->next; } } return(process_list); } } struct processjblock *removeJieader(ref_ptr) / * This function removes the refinement header and its channel list and returns a pointer to the refinement body. •/ struct processjblock *ref_ptr; { struct processjalock *p_ptr; struct channelJ>lock *c_ptrl, *c_ptr2; / * remove the channel list * / for (c_ptrl = ref_ptr->chanjist; c_ptrl != NULL; c_ptr2 = c_ptrl, c_ptrl = c_ptrl->next) { free(c_ptr2); } / * remove the process block */ p_ptr = ref_ptr-> refinement; free(ref_ptr); return(p_ptr); } out(channel_list,signal,chan_num,index) / • This routine dispatches a signal on the indicated channel. * / struct channel_block *channel_list; struct signal_block*signal; int chan_num, index; { extern int signal_pending; struct channel_block ^channel, *find_channel(); channel = find_channel(channel_list,chan_num,index); if (channel->target_channel->queued) { signal_pending++; signal->next = channel->target_channel->signal_list; channel->target_channel->signal_list = signal; } else / * rendez-vous * / { (*(channel->target_proc->proc_ptr))(channel->target_proc, channel,signal); } struct process_block *system_init() / * This routine causes the generation of the data structure and then check for dangling channel connections. */ { 57 struct processjblock *ptr, *processJist, *removeJieader(); struct channeljblock *c_ptr; / * user included del * / struct process_block *iohot_ref(); processjist = remove_header(iohot_ref(NULL)); for (ptr = processjist; ptr != NULL; ptr = ptr->next) { for (c_ptr = ptr->chanjist; c_ptr != NULL; c_ptr = c_ptr->next) { if (c_ptr->target_channel = = NULL) { / * oops a dangling connection * / fprintf(stderr,"OYSTEM INITIALIZATION ERROR: dangling"); fprintf(stderr," channel in an instance of ptr->pjdent); fprintf(stderr,"channel number %d, index %d0 ,c_ptr->cjd, c_ptr->index_num); } } } / * join the ends of the process list into a loop * / for (ptr = processjist; ptr->next != NULL; ptr = ptr->next); ptr-> next = processjist; return (processjist); } /* schedule(process_list) /* This is the main driving routine. struct process_b!ock *process_list; { extern int signal_pending; struct channel_block *c_ptr; struct signal_block *s_ptr, *get_signal(); struct process_block *p_ptr, *p_ptr2; p_ptr2 = process_Iist; P_ptr = process_Iist; c_ptr = p_ptr->chan_list; signal_pending =0; while (TRUE) { if (signal_pending > 0) { s_ptr = get_signal(&c_ptr, &p_ptr); signal_pending—; /* call the transition routine */ (*(p_ptr->proc_ptr))(p_ptr,c_ptr,s_ptr); /* move on to the next channel for the start of the next search */ if (c_ptr->next != NULL) c_ptr = c_ptr->next; else { p_ptr = p_ptr->next; c_ptr = p_ptr->chan_list; } if ((strcmp(p_ptr2->p_ident,"player_process") = = 0)) (*(p_ptr2->proc_ptr))(p_ptr2,NULL,NULL); p_ptr2 = p_ptr2->next; } } struct signal_block *get_signal(c_ptr,p_ptr) / • This function finds a pending signal on a signal queue. * / struct channel_block *(*c_ptr); struct process_block *(*p_ptr); { struct signal_block *s_ptr, *s_ptr2; int found= FALSE; for (; Ifound; (*p_ptr) = (*p_ptr)->next,(*c_ptr)=(*p_ptr)->cha { for (; ((*c_ptr) != NULL) && (Ifound); (*c_ptr)= (*c_ptr)->next) { if ((*c_ptr)->signal_list != NULL) { found = TRUE; if ((*c_ptr)->signaljist->next != NULL){ for (s_ptr = (*c_ptr)->signal_list, s_ptr2 = s_ptr->next; s_ptr2->next != NULL; s_ptr = s_ptr2, s_ptr2 = s_ptr2- > next); s_ptr->next = NULL; } else { s_ptr2 = (*c_ptr)->signal_list; (*c_ptr)->signal_list = NULL; } goto end; } } } end: return(s_ptr2); } add_index_block (channel, index) 7* This routine appends an index block on to the channels index list. struct channel_block *channel; int index; { struct index_block *ptr, *ptr2; ptr = ALLOCATE(index_block); ptr-> next = NULL; ptr->num = index; if (channel->index_list = = NULL) channel->index_list = ptr; else{ for (ptr2 = channel->index_list; ptr2->next != NULL; ptr2 = ptr2->next); ptr2->next = ptr; } /• ./ int get_index(channel, indexjpos) / • This routine retrives the index value store in an index block 61 The index_pos is origin zero * / struct channel_block *channel; int index_pos; { struct index_block *ptr; for (ptr = channel->index_list; index_pos > 0; ptr = ptr->next,index_pos—); return(ptr->num); } requeue(channel,signal) / • This routine puts the signal passed on to the head of the signal queue. * / struct channel_block *channel; struct signal_bk)ck *signal; { struct signal_block *ptr; extern int signal_pending; signal_pending++; if (channel->signal_list != NULL) { for (ptr = channel->signal_list; ptr->next != NULL; ptr=ptr->next); ptr->next = signal; } else channel->signal_list = signal; } 62 int random_select(low,high) / • This function returns a random integer between low and high, inclusive. • / int low, high; { long random(); float temp; temp = randomQ; temp = temp/0x7ffffflf; return((low + ((high - low + 1) * temp))/l); } Appendix HI Listdefs.h #define MAX_IDENT_LENGTH 30 #define T R U E #define FALSE #define ALLOCATE(A) 1 0 (struct A *)malloc(sizeof(struct A)); struct channel_block { struct channel_block •next; struct signal_block *signal_Iist; struct process_b'ock *target_proc; struct channel_block *target_channel; struct index_block *index_list; int queued; int c_id; int index_num; }; struct index_b'ock { struct index_b'ock *next; int num; }; 63 Appdenix IV Appendix IV: Alternating Bit Specification module ab_pc; end ab_pc; refinement ab_ref for ab_pc; const retran_time = 100; (* retranstission time *) type data_type = integer; seq_type = 0 .. 1; id_type = (A_DATA,ACK); timer_type = (retransmit); ndata_type= record id : id_type; data : data_type; seq : seq_type; end; msg_type = record msgdata : data_type; msgseq : seq_type; end; buffer_type= record flag : boolean; msg: msg_type; end; int_type = integer; (* channel definitions *) 64 channel U_receive_point(sender, receiver); by sender: RECEIVE_request; by receiver: RECErVE_response(UData: data_type); end U_receive_point; channel U_send_point(sender, receiver); by sender: SEND_request(UData : data_type); end U_send_point; type time_struct = array[timer_typej of record flag : boolean; sees : integer; millisecs : integer; end; channel S_access_point(User, Provider); by User: Timer_request(name : timer_type; time : integer); by Provider: Timer_response(Name: timer_type); end S_access_point; channel N_access_point(User, Provider); by User: Data_request(id:id_type; data: data_type; seq:seq_type); by Provider: Data_response(id:id_type; data: data_type; seq:seq_type); end N_access_point; (* *) channel network_channel(sender,receiver); by sender,receiver: packet(id:id_type; data: data_type; seq:seq_type); end network_channel; (* module definitions *) module Alternating_Bit; Us : U_send_point(receiver); ur : U_receive_point(receiver); N : N_access_point(User); S : S_access_point(User); end Alternating_Bit; process alternating_process for Alternating_Bit; QUEUED Us, Ur, N, S; var state: (ACK_WAIT, ESTAB); send_seq: seq_type; recv_seq: seq_type; send_buffer: buffer_type; recv_buffer: buffer_type; p,q: msg_type; function Ack_OK(id: id_type; seq,send_seq: seq_type) : boolean; begin Ack_OK := (id = ACK) and (seq = send_seq) end; initialize begin state send_seq recv_seq send_buffer.flag recv_buffer.fiag end; := ESTAB; = 0; = 0; = FALSE; = FALSE; (* transistions *) trans from ESTAB (* transition 1 *) to ACK_WAIT when Us.SEND_request provided not send_buffer.flag begin send_bufler.flag ;= true; send_buffer.msg.msgdata := UData; ,send_buffer.msg.msgseq := send_seq; out N.DATA_request(A_DATA,Udata, send_seq); out S.TIMER_request(retransmit,retran_time) end; trans from ESTAB, ACK_WAIT (* transition 2 *) to SAME when Ur.RECEIVE_request provided recv_bu8er.flag begin out Ur.RECErVE_response(recv_buffer.msg.msgdata); recv_buffer.flag := false; end; trans from ACK_WAIT (* transition 3 *) toACK_WAIT when S.TIMER_response provided Name = retransmit begin out N.DATA_request(A_DATA,send_buffer.msg.msgdata, send_buffer.msg.msgseq); out S.TIMER_request(retransmit,retran_time) end; trans from ESTAB (* transition 4 *) to ESTAB when S.TIMER_response provided Name = retransmit begin (* do nothing: the message that cause this timer to sent has been acknowledged. *) state := state end; trans from ACK_WAIT (* transition 5 *) to ESTAB when N.DATA_response provided Ack_OK(id, seq, send_seq) begin send_bufler.flag := false; send_seq := (send_seq + 1) mod 2 end; trans from ESTAB, ACK_WAIT (* transistion 6 *) to SAME when N.DATA_response provided id = A _ D A T A begin out N.DATA_request(ACK, data, seq); if seq = recv_seq then begin recv_buffer.flag := true; recv_buffer.msg.msgdata:= data; recv_buffer.msg.msgseq :=seq; recv_seq := (recv_seq + 1) mod 2 end end; end alternating_process; (*- *) (* timer module *) module timer; S : S_access_point(provider); 69 end timer; process timer_process for timer; QUEUED S; var index : a timer: timer_type; time_struct; procedure schedule_timeout(Var timer: time_struct; time_value: integer); primitive; predicate timer_expired(Var timer : time_struct); primitive; initialize begin for index := retransmit to retransmit do begin a_timer[index].flag := FALSE; a_timer[index] .sees := 0; a_timer[index] .millisecs end := 0 end; (*' transistions *) trans when S.Timer_request begin (* transistion 1 *) schedule_timeout(a_timer[Name],Time); end; any index:timer_type do (* transition 2 *) provided timer_expired(a_timer[index]) begin a_timer[index].flag := false; out S.Timer_response(index) end; end timer_process; (• *) (* network module *) module network; N : N_access_point(Provider); send_path : network_channel(sender); receive_path : network_channel(receiver); end network; process net_proc for network; QUEUED N, send_path, receive_path; trans when N.Data_request begin OUT send_path.packet(id, data, seq) end; trans when receive_path.packet begin OUT N.Data_response(id, data, seq) end; end net_proc; (* (* user module *) module the_user; Us : U_send_point(sender); Ur : U_receive_point(sender); end the_user; process user_process(number : integer) for the_user; QUEUED Us, Ur; type request_type = (send, receive); message_value_type = 1..9; var user_number : integer; initialize begin user_number := number end; trans when Ur.RECEIVE_response begin writeln('User ';user_number,' received the message ', UData); end; trans any request : request_type; message : message_value_type do provided request = send begin writeln('User ',user_number,' sent the message ', message); OUT Us.SEND_request(message); end; provided request = receive begin OUT Ur.RECEIVE_request end; end user_process; (* (* define some instances *) Al : Alternating_Bit with alternating_process; A2 : Alternating_Bit with alternating_process; timer 1 : timer with timer_process; timer2 : timer with timer_process; Nl : network with net_proc; N2 : network with net_proc; Ul : the_user with user_process(l); U2 : the_user with user_process(2); (* and connect them together *) CONNECT ALUs to Ul.Us; Al.Ur to Ul.Ur; Al.N to Nl.N; ALS to timerl.S; A2.Us to U2.Us; A2.Ur to U2.Ur; A2.N to N2.N; . A2.S to timer2.S; Nl.send_path to N2.receive_path; N2.send_path to Nl.receive_path; (* no replaces *) end ab_ref; Appendix V Utility Routines for Alternating Bit #include "inet.h" #define R O L E 1 / * or 0 */ out(channel_list,signal,chan_num,index) This routine dispatches a signal on the indicated channel. • / struct channel_block *channel_list; struct signal_block *signal; int chan_num, index; { extern int signal_pending, in_count, out_count; extern N E T _ C O N N conn; struct channel_block *channel, *find_channel(); int n; channel = find_channel(channel_list,chan_num,index); if ((channel->target_channel != NULL) && (channel->target_channel->queued) ) { signal_pending++; signal->next = channel->target_channel->signal_list; channel->target_channel->signal_list = signal; } else / * send it out on the network * / { buf[0] = signal->signal_id; buf[l] = signal-> Ivars.network_channel.packet.id; buf[2] = signal->lvars.network_channel.packet.data; 73 74 buf[3] = signal-> Ivars.network_channeI.packet.seq; free(signal); out_count++; if ((n =N_send(&conn,buf,16)) != N E T . O K ) { printf(">>> out : send problem %d ",n); exit(l); } } } struct process_block *system_init() / -This routine causes the generation of the data structure and then checl for dangling channel connections. •/ { struct process_block *ptr, *process_list, *remove_header(); struct channel_block *c_ptr; int n; /* user included del * / struct process_block *ioab_ref(); if (ROLE = = 1) /*server*/ { n = N_open(&conn,"T_portl@cs",CLSTWO); if (n != NET_OK) { printf(" > > > service : N_open error %dO,n); exit(l); } n = N_accept(&conn); if (n != NET_OK) { printf(">>> service : N_accept error %dO,n); exit(l); } } else { if ((n = N_connect(&conn, "T_portl@cs",CLSTWO)) != NET_OK) { printf(">>> receiver : N_connect error %d",n); exit(l); } } process_list = remove_header(ioab_ref(NULL)); for (ptr = processjist; ptr != NULL; ptr = ptr->next) { for (c_ptr = ptr->chanjist; c_ptr != NULL; c_ptr = c_ptr->next) { if (c_ptr->target_channel = = NULL) { / * oops a dangling connection * / fprintf(stderr,"OYSTEM INITIALIZATION ERROR: dangling"); fprintf(stderr," channel in an instance of ptr->pjdent); fprintf(stderr,"channel number %d, index %d0,c_ptr->cjd, c_ptr- > index_num); } } } / * join the ends of the process list into a loop * / for (ptr = processjist; ptr->next != NULL; ptr = ptr->next); ptr-> next = processjist; return(processjist); } schedule(process_Iist) / * This is the main driving routine. * / struct process_bk>ck *process_list; { extern int signal_pending; extern int in_count, out_count; struct channe l_block *c_ptr; struct signal_block *s_ptr, *get_signal(); struct process_block *P_ptr, *p_ptr2; p_ptr2 = process_list; p_ptr = process_list; c_ptr = p_ptr->chan_Iist; signal_pending =0; while ( (in_count < 5) || (out_count <5)) / * arbitrary stop condition * / { if ((s_ptr = get_signal(&c_ptr, &p_ptr)) != NULL) { / * call the transition routine */ (*(p_ptr->proc_ptr))(p_ptr,c_ptr,s_ptr); } / * move on to the next channel for the start of the next search */ if (c_ptr->next != NULL) c_ptr = c_ptr->next; else { p_ptr = p_ptr->next; c_ptr = p_ptr->chan_list; } if ((strcmp(p_ptr2->p_ident,"timer_process") = = 0) || (strcmp(p_ptr2->p_ident,"user_process'') = = 0)) (*(p_ptr2->proc_ptr))(p_ptr2,NULL,NULL); p_ptr2 = p_ptr2->next; } N_close(&conn); } struct signal_block *get_signal(c_ptr,p_ptr) / * This function finds a pending signal on a signal queue. • / struct channel_block *(*c_ptr); struct process_Mock *(*P_ptr); { struct signal_bl° c k *s_ptr, *s_ptr2; int found= FALSE; int n, temp; extern N E T _ C O N N conn; extern int in_count, out_count; static int count; s_ptr2 = NULL; for (;!found; (*p_ptr) = (*p_ptr)->next,(*c_ptr)=(*p_ptr)->chan_Iist, s_ptr2 = NULL) { for (; (((*c_ptr) != NULL) && (Ifound)); (*c_ptr)= (*c_ptr)->next) { if ((*c_ptr)->signaljist != NULL) { found = TRUE; if ((*c_ptr)->signal_list->next != NULL){ for (s_ptr = (*c_ptr)->signal_list, s_ptr2 = s_ptr->next; s_ptr2->next != NULL; s_ptr = s_ptr2, s_ptr2 = s_ptr2->next); s_ptr->next = NULL; } else { s_ptr2 = (*c_ptr)->signal_list; (*c_ptr)->signal_list = NULL; } goto end; } if ((strcmp((*p_ptrr>p_ident,"net_proc") = = 0) && ((*c_ptr)->c_id = = 3)) { if ((n = N_receive(&conn, buf, buffsize)) < = 0) { if (n < 0) { printf(" read error %d0,n); exit(l); } } else { s_ptr2 = ALLOCATE(signal_block); s_ptr2->signal_id = buf[0]; s_ptr2->lvars.network_channel.packet.id = buf[l]; s_ptr2->lvars.network_channel.packet.data = buf[2] s_ptr2->lvars.network_channel.packet.seq = buf[3]; in_count++; goto end; } s_ptr2 = NULL; goto end; } } } end: return(s_ptr2); } /* ^include <sys/types.h> #include <sys/timeb.h> #include "listdefs.h" struct time_struct { int flag; int int }; sees; millisecs; schedule_timeout(timer,time_value) / * . This routine places in the timer passed the value of present time + "time_value" which will be tested later by "timer_expired". The units of time_value are milliseconds. •/ struct time_struct *timer; int time_value; { struct timeb *tp; ftime(tp); timer-> flag = TRUE; timer-> sees = tp->time; timer- >millisecs= tp->millitm; if ((time_value = time_value + tp->millitm) > = 1000) { timer->secs++; timer->millisecs = time_value - 1000; } } int timer_expired(timer) / * This predicate returns T R U E if the timer passed has expired and cancels it if it has struct time_struct *timer; { struct timeb *tp; ftime(tp); if ((timer->flag = = TRUE) && (timer-> sees < tp->time) && (timer->millisecs < tp->millitm)) return(TRUE); else return(FALSE); } cancel_timer(timer) /*• This routine cancels the timer passed • / struct time_struct *timer; { timer->flag = FALSE; } Appendix VI Alternating Bit Implementation Code #include <stdio.h> #include <strings.h> #include "listdefs.h" /*• type code * / typedef int data_type; typedef int seq_type; typedef int id_type; typedef int timer_type; typedef struct { id-type id; data_type data; seq_type seq; } ndata_type; typedef struct { data_type msgdata; seq_type msgseq; } msg_type; typedef struct { int flag; msg_type msg; } buffer_type; typedef int int_type; typedef struct { int flag; int sees; int millisecs; } time_struct[l]; typedef int request_type; typedef int message_value_type; /. •/ / * signal block del * / 81 struct signal_block { int signal_id; struct signaI_block *next; union { struct { struct { data_type udata; } receive_response; } u_receive_point; struct { struct { data_type udata; } send_request; } u_send_point; struct { struct { timer_type name; int time; } timer_request; struct { timer_type name; } timer_response; } s_access_point; struct { struct { id_type id; data_type data; seq_type seq; } data_request; struct { id_type id; data_type data; seq_type seq; } data_response; } n_access_point; struct { struct { id_type id; data_type data; seq_type seq; } packet; } network_chanrel; } lvars; }; / * process del code * / struct process_block { struct process_block *next; char p_ident[MAX_IDENT_LENGTH+l]; struct channelJ>lock *chan_list; struct process_block *refinement; int (*proc_ptr)(); union { struct { int state; seq_type send_seq; seq_type recv_seq; buffer_type send_buffer; buffer_type recvJbuffer; msg_type p, q; } s_alternating_process; struct { timer_type index; time_struct a_timer; } s_t im e r_p roc ess; struct { int user_number; int count; } s_user_process; } lvars; }; /. -*/ / * procedure code * / struct process_block *ioab_ref(p_block) struct process_block *p_block; { struct processJ>lock *ioaIternating_process(); struct processjblock *iotimer_process(); struct processjblock *ionet_proc(); struct processjilock *iouser_process(); struct channeljjlock *add_channelJ>lock(), *c_ptr; struct processjblock *add_refinementjieader(), *clean_up(), •processjist; processjist = NULL; processjist = ioalternating_process(processJist); processjist = iotimer_process(processjist); processjist = ionet_proc(processJist); processjist = iouser_process(processjist,l); connect_ports(processJist,-l, 1, 0, 1, 1, 0); connect_ports(processJist,4, 2, 0, 1, 2, 0); connect_ports(processJist,4, 3, 0, 2, 1, 0); connect_ports(processJist,4, 4, 0, 3, 1, 0); pjblock = add_refinement_header(p_b'ock,processJist); pJb'ock-> refinement = clean_up(p_block-> refinement); return(pjblock); } /• */ struct processjblock *ioalternating_process(processjist) struct processjblock *processJist; { struct processjblock *pJblock, *add_processJ>lock(); extern int alternating_process(); struct channeljblock *add_channelJ>lock(), *c_ptr; pjblock = add_processjblock(processjist,alternating_process, " altera ating_processn); pjblock- > chanjist = add_channelJblock(pJblock->chanJist, &c_ptr,TRUE,l,0); p_block-> chanjist = add_channel_block(pJblock->chanJist, &c_ptr,TRUE,2,0); pjblock-> chanjist = add_channeljblock(pjblock->chanjist, &c_ptr,TRUE,3,0); pjblock-> chanjist = add_channel_block(p_block->chanJist, &c_ptr,TRUE,4,0); pJblock-> Ivars. s_alternating_process.state = 1; p_block-> Ivars.s_alternating_process.send_seq == 0; pJblock-> Ivars. s_alternating_process.recv_seq = 0; pJblock-> Ivars.s_alternating_process.sendJbuffer.flag = 0; p_block-> Ivars.s_alternating_process.recvJbuffer.flag = 0; return(pjblock); } /* */ alternating_process(pJblock,channel,signal) struct processjblock *p_block; struct channeljblock *channel; struct signaljblock *signal; { struct signaljblock *s_ptr; if ((channel != NULL) && ((pjblock->lvars.s_alternating_process.state = = 1))) if ((channel->cjd = = 1) && (signal->signaljd = = 2)) { if (!(p_block->lvars.s_altemating_process.sendJbuffer.flag)){ p_block->lvars.s_alternating_process.state = 0 ; { p_block->lvars.s_alternating_process.sendJbuffer.flag = 1 p_blc«k->lvars.s_alternatrag_process.send_bufl"er.msg.rnsgdata = sign al-> lv ars. u_sead_poin t .send_reques t. ud ata; p_blc*k->lvars.s_alternating_process.send_buffer.msg.msgseq = p_b loc k- > lv ars .s_altern ating_process .send_seq; s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 5; s_ptr->lvars.n_access_point.data_request.id = 0; s_ptr->lvars.n_access_point.data_request.data = signal->lvars.u_send_point.send_request.udata; s_ptr-> lvars.n_access_point.data_request.seq = p_block->lvars.s_alternating_process.send_seq; out(p_block->chan_list,s_ptr,3,0); s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 3; s_ptr->lvars.s_access_point.timer_request.name = 0; s_ptr->lvars.s_access_point.timer_request.time = 100; out(p block->chan_list,s_ptr,4,0); } goto dispose; } } if ((channel != NULL) && ((p_block->lvars.s_alternating_process.state = = 1 ) || (p_block->lvars.s_alternating_process.state = = 0))) if ((channel->c_id = = 2) && (signal->signal_id = = 0)) { if (p_block-> lvars.s_alternating_process.recv_buffer.flag){ { s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 1; s_ptr-> lvars.u_receive_point.receive_response.udata = p_block-> Ivars.s_alternating_process.recv_buffer.msg.msgdata; out(p_block->chan_Iist,s_ptr,2,0); p_block-> Ivars.s_alternating_process.recv_buffer.flag = 0; } goto dispose; } } if ((channel != NULL) && ((p_block->lvars.s_alternating_process.state = = 0))) if ((channel->c_id = = 4) && (signal->signal_id = = 4)) { if ((signal->lvars.s_access_point.timer_response.name = = 0)){ p_block->lvars.s_alternating_process.state = 0 ; { s_ptr = ALLOCATE(signaI_block); s_ptr->signal_id = 5; s_ptr->lvars.n_access_point.data_request.id = 0; 8_ptr->lvars.n_access_point.data_request.data = p_bIock->lvars.s_alternating_process.send_buffer.msg.msgdata; s_ptr-> lvars.n_access_point.data_request.seq = p_block->lvars.s_alternating_process.send_buffer.msg.msgseq; out(p_block->chan_Iist,s_ptr,3,0); s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 3; s_ptr->lvars.s_access_point.timer_request.name = 0; s_ptr->lvars.s_access_point.timer_request.time = 100; out(p_block->chan_list,s_ptr,4,0); } goto dispose; } } if ((channel != NULL) && ((p_blc-ck->lvars.s_alternating_process.state = = 1))) if ((channel->c_id = = 4) && (signal->signal_id = = 4)) { if ((signal->lvars.s_access_point.timer_response.name = = 0)){ p_block->lvars.s_alternating_process.state = 1 ; { p_block->lvars.s_alternating_process.state = p_block->lvars.s_alternating_process.state; } goto dispose; } } if ((channel != NULL) && ((p_block->lvars.s_alternating_process.state = = 0))) if ((channel->c_id = = 3) && (signal->signal_id = = 6)) { if (ack_ok(signal->lvars.n_access_point.data_response.id, signal- > lvars.n_access_point.data_response.seq, p_block->lvars.s_alternating_process.send_seq)){ p_block->lvars.s_alternating_process.state = 1 ; { p_block->lvars.s_alternating_process.send_buffer.flag = 0; p_block->lvars.s_alternating_process.send_seq = (((p_block->lvars.s_alternating_process.send_seq + 1)) % 2); } goto dispose; } } if ((channel != NULL) && ((p_block->lvars.s_alternating_proces8.state =—= 1 ) | | (p_block->lvars.s_alternating_process.state = = 0))) if ((channel->c_id = = 3) && (signal-> signal_id = = 6)) { if ((signal->lvars.n_access_point.data_response.id = = 0)){ { s_ptr = ALLOCATE(signal_biock); s_ptr->signal_id = 5; s_ptr-> lvars. n_access_point.data_request.id = 1; s_ptr-> lvars. n_access_point.data_request. data = signal- > lvars.n_access_point.data_response.data; s_ptr-> lvars.n_access_point.data_request.seq = signal->lvars.n_access_point.data_response.seq; out(p_block->chan_list,s_ptr,3,0); if((signal->lvars.n_access_point.data_response.seq = = p_bIock->lvars.s_alternating_process.recv_seq)) { { p_block->lvars.s_alternating_process.recv_buffer.flag = 1; p_block->lvars.s_alternating_process.recv_buffer.msg.msgdata = signal->lvars.n_access_point.data_response.data; p_block->lvars.s_alternating_process.recv_bun"er.msg.msgseq = signal- > lv ars. n_access_poin t.data_response.seq; p_block->lvars.s_alternating_process.recv_seq = (((p_block->lvars.s_alternating_process.recv_seq + 1)) % 2); } } } goto dispose; } } if (channel != NULL) { requeue(channel,signal); signal=NULL; } dispose: free(signal); } /* •/ int ack_ok(id,seq,send_seq)id_type id; seq_type seq, send_seq; { int rtv_ack_ok; { rtv_ack_ok = (((id === 1)) && ((seq = = send_seq))); } return(rtv_ack_ok); } /* */ struct process_block *iotimer_process(process_list) struct process_block *processJist; { struct processjblock *p_block, *add_processj)lock(); extern int timer_process(); struct channelJ>lock *add_channelJ>lock(), *c_ptr; pjjlock = add_processJjlock(processJist,timer_process,"timer_process"); pJ>lock->chanJist -= add_channelJjlock(p_block->chanJist,&c_ptr,TRUE,l,0); for (pJ)lock->lvars.s_timer_process.index = 0; p_block-> lvars.s_timer_process.index++ <= 0;){ { pJ>lock->lvars.s_timer_process.a_timer( pj5lock->lvars.s_timer_process.index].flag = 0; pJ>lock->lvars.s_timer_process.a_timer[ pJjlock->lvars.s_timer_process.index] .sees = 0; pJjlock->lvars.s_timer_process.a:_timer[ pJ>lock->lvars.sJimer_process.index].millisecs = 0; } } return(p_bk>ck); } / . -—*/ timer_process(p_block,channel,signal) struct process_block *p_block; struct channeI_block *channel; struct signaljblock *signal; { struct signal_block *s_ptr; if ((channel != NULL) ) if ((channel->c_id = = 1) && (signal->signal_id = = 3)) { { { schedule_timeout(&p_block->lvars.s_timer_process.a_timer[ signal- > lv ars.s_access_poin t. timer_request.n ame], signal->lvars.s_access_point.timer_request.time); } goto dispose; } } if (channel != NULL) { requeuefchannel,signal); signal=NULL; } { timer_type index; index = random_select(0,0 ); if (timer_expired(&p_block-> lvars.8_timer_process.a_timer[index])) { { p_b'ock->lvars.s_timer_process.a_timer[index].flag = 0; s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 4; s_ptr->lvars.s_access_point.timer_response.name = index; out(p_b!ock- > chan_list,s_ptr, 1,0); } goto dispose; } } dispose: free(signal); } /* */ struct process_block *ionet_proc(process_list) struct process_block *process_list; 89 { struct process_block *p_block, *add_process_block(); extern int net_proc(); struct channeljblock *add_channel_block(), *c_ptr; p_block = add_process_block(process_list,net_proc,"net_proc''); p_block->chan_list = add_channel_block(p_block->chanJist,&c_ptr,TRUE,l,0); p_block->chan_list = add_channel_block(p_block->chan_list,&c_ptr,FALSE,2,0); p_block->chan_list = add_channeI_block(p_block->chan_Iist,&c_ptr,TRUE,3,0); return(p_block); } /* •/ net_proc(p_block,channel,signal) struct process_block *p_block; struct channeljblock *channel; struct signal_block *signal; { struct signal_block *s_ptr; if ((channel != NULL) ) if ((channel->cjd = = 1) && (signal->signaljd = = 5)) { v { { s_ptr = ALLOCATE(signal_block); s_ptr->signaljd = 7; s_ptr->lvars.network_channel.packet.id = sign al-> lvars.n_access_point.data_request.id; s_ptr->lvars.network_channel.packet.data = signal->lvars.n_access_point.data_request.data; s_ptr->lvars.network_channel.packet.seq = signal-> lvars.n_access_point.data_request.seq; out(p_block->chan_list,s_ptr,2,0); } goto dispose; } } if ((channel != NULL) ) if ((channel->c_id = = 3) && (signal->signal_id = = 7)) { { { s_ptr = ALLOCATE(signal_block); s_ptr-> signal J d = 6; s_ptr->lvars.n_access_point.data_response.id == signal-> lvars.network_channel. packet.id; s_ptr->lvars.n_access_point.data_response.data = signal->lvars.network_channel.packet.data; s_ptr->lvars.n_access_point.data_response.seq = signal->lvars.network_channel.packet.seq; out(p_block->chan _list,s_ptr,l,0); } goto dispose; } } if (channel != NULL) { requeue(channel,signal); signal=NULL; } dispose: free(signal); } /. ./ struct process_block *iouser_process(process_list,number) struct process_block *process_list; int number; { struct process_b!° ck *p_block, *add_process_block(); extern int user_process(); struct channel_block *add_channel_bIock(), *c_ptr; p_block = add_process_block(process_list,user_process,"user_process"); p_block->chan_list = add_channel_block(p_block->chan_list,&c_ptr,TRUE,l,0); p_block->chan_list = add_channel_block(p_block->chan_list,&c_ptr,TRUE,2,0); p_block->lvars.s_user_process.user_number = number; p_block-> Ivars. s_user_process. count == 0; return(p_block); } /* */ user_process(p_block, channel, signal) struct process_block *p_block; struct channel_block *channel; struct signal_bIock *signal; { struct signaI_block *s_ptr; if ((channel != NULL) ) if ((channel->c_id = = 2) && (signal->signal_id = = 1)) { { { printf("User "); printf("%d",p_block->lvars.s_user_process.U8er_number); printf(" received the message "); printf(" %d", signal- >lv ars. u_receive_point.receive_response.udata); printf("0); } goto dispose; } } if (channel != NULL) { requeuefchannel,signal); signal=NULL; } { request_type request; message_value_type message; request = random_select(0,l ); message == random_se!ect(l,9 ); if ((request = = 1)) { { s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 0; out(p_Mock->chan_list,s_ptr,2,0); } goto dispose; } } { request_type request; message_value_type message; request = random_select(0,l ); message = random_select(l,9 ); if ((((request = = 0)) && ((p_block->lvars.s_user_process.count < 5)))) { { printf("User "); printf("%d",p_block->lvars.s_user_process.user_number); printf(" sent the message "); printf("%d ".message); printf("0); p_block-> Ivars.s_user_process.count = (p_block->lvars.s_user_process.count + l); s_ptr = ALLOCATE(signal_block); s_ptr->signal_id = 2; s_ptr-> Ivars. u_send _point.send_request.udata = message; out(p_bJock->chan_list,s_ptr,l,0); } goto dispose; } } dispose: free(signal); } /. */ #include "fdtutil.c" Appendix VLT Running The Compiler To run the compiler is simple. Simply enter: - fdt <inputfile >fdt.c The outputfile fdt.c will contain the generated C code which is compiled and linked with the utility routines with the following command: - make This runs the make command which knows how to "make" programs, see the manual for further details. 

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