Man page - sem_getvalue(3)

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Manual

sem_getvalue

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
STANDARDS
HISTORY
NOTES
SEE ALSO

NAME

sem_getvalue - get the value of a semaphore

LIBRARY

POSIX threads library ( libpthread , -lpthread )

SYNOPSIS

#include <semaphore.h>

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

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. (The glibc implementation currently does not check whether sem is valid.)

ATTRIBUTES

For an explanation of the terms used in this section, see attributes (7).

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STANDARDS

POSIX.1-2008.

HISTORY

POSIX.1-2001.

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)