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Name

sem_getvalue - get the value of a semaphore

Synopsis


#include <semaphore.h>
int sem_getvalue(sem_t *sem, int *sval);

Link with -pthread.

Description

sem_getvalue() places the current value of the semaphore pointed to sem into the integer pointed to by sval.

If one or more processes or threads are blocked waiting to lock the semaphore with sem_wait(3) , POSIX.1-2001 permits two possibilities for the value returned in sval: either 0 is returned; or a negative number whose absolute value is the count of the number of processes and threads currently blocked in sem_wait(3) . Linux adopts the former behavior.

Return Value

sem_getvalue() returns 0 on success; on error, -1 is returned and errno is set to indicate the error.

Errors

EINVAL
sem is not a valid semaphore.

Attributes

Multithreading (see pthreads(7) )

The sem_getvalue() function is thread-safe.

Conforming to

POSIX.1-2001.

Notes

The value of the semaphore may already have changed by the time sem_getvalue() returns.

See Also

sem_post(3) , sem_wait(3) , sem_overview(7)

Colophon

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