103 lines
2.4 KiB
Plaintext
103 lines
2.4 KiB
Plaintext
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(* Version 1.10, Nov 1984 *)
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DEFINITION MODULE Processes;
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(*
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(pseudo-) concurrent programming with SEND/WAIT
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From the book 'Programming in Modula-2' by Prof.
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N. Wirth.
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*)
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EXPORT QUALIFIED
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SIGNAL, SEND, WAIT,
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StartProcess, Awaited, Init;
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TYPE
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SIGNAL;
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(*
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- SIGNAL's are the means of synchronization between
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processes. Any variable of type SIGNAL must be
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initialized explizitly by means of procedure
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'Init' before using it with any other procedure
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of this module.
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*)
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PROCEDURE StartProcess (P: PROC; n: CARDINAL);
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(*
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- Start up a new process.
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in: P top-level procedure that will execute in this
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process.
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n number of bytes of workspace to be allocated
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to it.
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Allocates (from Storage) a workspace of n bytes, and
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creates a process executing procedure P in that workspace.
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Control is given to the new process.
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Caution: The caller must ensure that the workspace size is
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sufficient for P.
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Errors: StartProcess may fail due to insufficient memory.
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*)
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PROCEDURE SEND (VAR s: SIGNAL);
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(*
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- Send a signal
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in: s the signal to be sent.
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out: s the signal with one less process waiting
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for it.
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If no process is waiting for s, SEND has precisely no
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effect. Otherwise, some process which is waiting for s
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is given control and allowed to continue from WAIT.
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*)
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PROCEDURE WAIT (VAR s: SIGNAL);
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(*
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- Wait for some other process to send a signal.
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in: s the signal to wait for.
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The current process waits for the signal s. At some later
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time, a SEND(s) by some other process can cause this
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process to return from WAIT.
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Errors: If all other processes are waiting, WAIT
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terminates the program.
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*)
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PROCEDURE Awaited (s:SIGNAL): BOOLEAN;
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(*
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- Test whether any process is waiting for a signal.
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in: s the signal of interest.
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out: TRUE if and only if at least one process is
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waiting for s.
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*)
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PROCEDURE Init (VAR s: SIGNAL);
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(*
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- Initialize a SIGNAL object.
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in: s the signal to be initialized
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out: s the initialized signal (ready to be used
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with one of the procedures declared above)
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An object of type SIGNAL must be initialized with this
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procedure before it can be used with any of the other
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operations. After initilization of s, Awaited(s) is FALSE.
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*)
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END Processes.
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