SEM_GETVALUE(3) - man page online | library functions

Get the value of a semaphore.

SEM_GETVALUE(3)                     Linux Programmer's Manual                     SEM_GETVALUE(3)

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 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 pro‐ cesses 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 For an explanation of the terms used in this section, see attributes(7). ┌───────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├───────────────┼───────────────┼─────────┤ │sem_getvalue() │ Thread safety │ MT-Safe │ └───────────────┴───────────────┴─────────┘
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 This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at
Linux 2015-08-08 SEM_GETVALUE(3)
This manual Reference Other manuals
sem_getvalue(3) referred by rights(4freebsd) | sem(4freebsd) | sem_close(3) | sem_open(3) | sem_overview(7) | sem_post(3) | sem_unlink(3) | sem_wait(3)
refer to attributes(7) | sem_overview(7) | sem_post(3) | sem_wait(3)