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(3P)					     POSIX Programmer's Manual						  SEM_GETVALUE(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       sem_getvalue -- get the value of a semaphore

SYNOPSIS

       #include <semaphore.h>

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

DESCRIPTION

       The sem_getvalue() function shall update the location referenced by the sval argument to have the value of the semaphore referenced by  sem
       without 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 object to which sval points shall either be set to zero or to a negative number whose absolute value	represents
       the number of processes waiting for the semaphore at some unspecified time during the call.

RETURN VALUE

       Upon  successful  completion,  the  sem_getvalue()  function shall return a value of zero. Otherwise, it shall return a value of -1 and set
       errno to indicate the error.

ERRORS

       The sem_getvalue() function may fail if:

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

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       semctl(), semget(), semop(), sem_post(), sem_timedwait(), sem_trywait()

       The Base Definitions volume of POSIX.1-2008, <semaphore.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							  SEM_GETVALUE(3P)