gm2-libs-iso/Semaphores

DEFINITION MODULE Semaphores;

  (* Provides mutual exclusion facilities for use by processes. *)

TYPE
  SEMAPHORE;

Create
PROCEDURE Create (VAR s: SEMAPHORE; initialCount: CARDINAL );
  (* Creates and returns s as the identity of a new semaphore that
     has its associated count initialized to initialCount, and has
     no processes yet waiting on it.
  *)

Destroy
PROCEDURE Destroy (VAR s: SEMAPHORE);
  (* Recovers the resources used to implement the semaphore s,
     provided that no process is waiting for s to become free.
  *)

Claim
PROCEDURE Claim (s: SEMAPHORE);
  (* If the count associated with the semaphore s is non-zero,
     decrements this count and allows the calling process to
     continue; otherwise suspends the calling process until
     s is released.
  *)

Release
PROCEDURE Release (s: SEMAPHORE);
  (* If there are any processes waiting on the semaphore s,
     allows one of them to enter the ready state; otherwise
     increments the count associated with s.
  *)

CondClaim
PROCEDURE CondClaim (s: SEMAPHORE): BOOLEAN;
  (* Returns FALSE if the call Claim(s) would cause the calling
     process to be suspended; in this case the count associated
     with s is not changed. Otherwise returns TRUE and the
     associated count is decremented.
  *)

END Semaphores.