33 lines
851 B
Modula-2
33 lines
851 B
Modula-2
DEFINITION MODULE Semaphores;
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(*
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Module: Processes with semaphores
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Author: Ceriel J.H. Jacobs
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Version: $Id$
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On systems using quasi-concurrency, the only opportunities for process-
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switches are calls to Down and Up.
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*)
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TYPE Sema;
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PROCEDURE Level(s: Sema) : CARDINAL;
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(* Returns current value of semaphore s *)
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PROCEDURE NewSema(n: CARDINAL) : Sema;
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(* Creates a new semaphore with initial level "n" *)
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PROCEDURE Down(VAR s: Sema);
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(* If the value of "s" is > 0, then just decrement "s".
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Else, suspend the current process until the semaphore becomes
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positive again.
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*)
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PROCEDURE Up(VAR s: Sema);
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(* Increment the semaphore "s".
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*)
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PROCEDURE StartProcess(P: PROC; n: CARDINAL);
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(* Create a new process with procedure P and workspace of size "n".
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Also transfer control to it.
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*)
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END Semaphores.
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