The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


sem_getvalue - get the value of a semaphore (REALTIME)


#include <semaphore.h>

int sem_getvalue(sem_t *sem, int *sval);


The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.

If sem is locked, then the value returned by sem_getvalue() is either zero or a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.


Upon successful completion, the function returns a value of zero. Otherwise, the function returns a value of -1 and sets errno to indicate the error.


The sem_getvalue() function will fail if:
The sem argument does not refer to a valid semaphore.
The function sem_getvalue() is not supported by this implementation.








semctl(), semget(), semop(), sem_post(), sem_trywait(), sem_wait(), <semaphore.h>.


Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)

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Copyright © 1997 The Open Group
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