php man page for sem_getvalue

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 4.15 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								    2017-09-15							   SEM_GETVALUE(3)