Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- get the value of a semaphore
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
function shall update the location referenced by the
argument to have the value of the semaphore referenced by
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.
is locked, then the object to which
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.
Upon successful completion, the
function shall return a value of zero. Otherwise, it shall return
a value of -1 and set
to indicate the error.
function may fail if:
argument does not refer to a valid semaphore.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
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 Standard
is the referee document. The original Standard can be obtained online at
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