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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(3P)					     POSIX Programmer's Manual						  SEM_GETVALUE(3P)

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond- ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. NAME
sem_getvalue - get the value of a semaphore (REALTIME) SYNOPSIS
#include <semaphore.h> int sem_getvalue(sem_t *restrict sem, int *restrict sval); DESCRIPTION
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. ERRORS
The sem_getvalue() function shall fail if: EINVAL The sem argument does not refer to a valid semaphore. The following sections are informative. EXAMPLES
The sem_getvalue() function is part of the Semaphores option and need not be available on all implementations. RATIONALE
semctl(), semget(), semop(), sem_post(), sem_timedwait(), sem_trywait(), sem_wait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at . IEEE
/The Open Group 2003 SEM_GETVALUE(3P)
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