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Linux 2.6 - man page for sem_getvalue (linux section 3)

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.1-2001 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.

CONFORMING TO
       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)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux					    2012-05-13				  SEM_GETVALUE(3)


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