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 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 4.10 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
       https://www.kernel.org/doc/man-pages/.



Linux				  2015-08-08		       SEM_GETVALUE(3)