Copyright (C) 2006 Michael Kerrisk <firstname.lastname@example.org> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. ...
NAMEsem_getvalue - get the value of a semaphore
#include <semaphore.h> int sem_getvalue(sem_t *sem, int *sval);
Link with -pthread.
DESCRIPTIONsem_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 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 VALUEsem_getvalue() returns 0 on success; on error, -1 is returned and errno is set to indicate the error.
- sem is not a valid semaphore.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).