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sem_getvalue(3) [v7 man page]

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

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 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
For an explanation of the terms used in this section, see attributes(7). +---------------+---------------+---------+ |Interface | Attribute | Value | +---------------+---------------+---------+ |sem_getvalue() | Thread safety | MT-Safe | +---------------+---------------+---------+ CONFORMING TO
POSIX.1-2001, POSIX.1-2008. 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 4.15 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 2017-09-15 SEM_GETVALUE(3)

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sem_getvalue(3C)					   Standard C Library Functions 					  sem_getvalue(3C)

sem_getvalue - get the value of a semaphore SYNOPSIS
#include <semaphore.h> int sem_getvalue(sem_t *restrict sem, int *restrict sval); DESCRIPTION
The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem with- out 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. The value set in sval may be 0 or positive. If sval is 0, there may be other processes (or LWPs or threads) waiting for the semaphore; if sval is positive, no process is waiting. RETURN VALUES
Upon successful completion, sem_getvalue() returns 0. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The sem_getvalue() function will fail if: EINVAL The sem argument does not refer to a valid semaphore. ENOSYS The sem_getvalue() function is not supported by the system. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
semctl(2), semget(2), semop(2), sem_post(3C), sem_wait(3C), attributes(5), standards(5) SunOS 5.11 5 Feb 2008 sem_getvalue(3C)
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