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.
sem_getvalue — get the value of a semaphore
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
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.
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.
The sem_getvalue() function may fail if:
- The sem argument does not refer to a valid semaphore.
The following sections are informative.
semctl(), semget(), semop(),
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 http://www.opengroup.org/unix/online.html .
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