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DEFINITION MODULE Semaphores; (* Provides mutual exclusion facilities for use by processes. *) TYPE SEMAPHORE; 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, or raises an exception if a new semaphore cannot be created. *) PROCEDURE Destroy (VAR s: SEMAPHORE); (* Provided that no process is waiting for s to become free, recovers the resources used to implement the semaphore s. *) 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. *) 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. *) 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. *) PROCEDURE IsSemaphoresException (): BOOLEAN; (* Returns TRUE if the current coroutine is in the exceptional execution state because of the raising of the Semaphores exception; otherwise returns FALSE. *) END Semaphores. |