sem_getvalue(3) [mojave man page]

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)

sem_getvalue(3RT)					    Realtime Library Functions						 sem_getvalue(3RT)

NAME

       sem_getvalue - get the value of a semaphore

SYNOPSIS

       cc [ flag... ] file... -lrt [ library... ]
       #include <semaphore.h>

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

DESCRIPTION

       The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem with-
       out affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred  at  some  unspecified  time
       during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.

       If  sem is locked, then the value returned by sem_getvalue() is either zero or a negative number whose absolute value represents the number
       of processes waiting for the semaphore at some unspecified time during the call.

       The value set in sval may be 0 or positive. If sval is 0, there may be other processes (or LWPs or threads) waiting for the  semaphore;	if
       sval is positive, no process is waiting.

RETURN VALUES

       Upon successful completion, sem_getvalue() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

       The  sem_getvalue() function will fail if:

       EINVAL	       The sem argument does not refer to a valid semaphore.

       ENOSYS	       The sem_getvalue() function is not supported by the system.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       semctl(2), semget(2), semop(2), sem_post(3RT), sem_wait(3RT), attributes(5), standards(5)

SunOS 5.10							    1 Nov 2003							 sem_getvalue(3RT)