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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 3.53 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)