sem_getvalue - Man Page

get the value of a semaphore


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <semaphore.h>

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


The sem_getvalue() function shall update 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 object to which sval points shall either be set to zero or to a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.

Return Value

Upon successful completion, the sem_getvalue() function shall return a value of zero. Otherwise, it shall return a value of -1 and set errno to indicate the error.


The sem_getvalue() function may fail if:


The sem argument does not refer to a valid semaphore.

The following sections are informative.



Application Usage




Future Directions


See Also

semctl(), semget(), semop(), sem_post(), sem_timedwait(), sem_trywait()

The Base Definitions volume of POSIX.1-2017, <semaphore.h>

Referenced By

semaphore.h(0p), semctl(3p), semget(3p), semop(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual