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NAME

       sem_getvalue - get the value of a semaphore

SYNOPSIS

       #include <semaphore.h>

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

       Link with -lrt or -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

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