SEM_TRYWAIT
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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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.
NAME
sem_trywait,
sem_wait
--- lock a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_trywait(sem_t *sem);
int sem_wait(sem_t *sem);
DESCRIPTION
The
sem_trywait()
function shall lock the semaphore referenced by
sem
only if the semaphore is currently not locked; that is, if the
semaphore value is currently positive. Otherwise, it shall not lock
the semaphore.
The
sem_wait()
function shall lock the semaphore referenced by
sem
by performing a semaphore lock operation on that semaphore. If the
semaphore value is currently zero, then the calling thread shall not
return from the call to
sem_wait()
until it either locks the semaphore or the call is interrupted by a
signal.
Upon successful return, the state of the semaphore shall be locked and
shall remain locked until the
sem_post()
function is executed and returns successfully.
The
sem_wait()
function is interruptible by the delivery of a signal.
RETURN VALUE
The
sem_trywait()
and
sem_wait()
functions shall return zero if the calling process successfully
performed the semaphore lock operation on the semaphore designated by
sem.
If the call was unsuccessful, the state of the semaphore shall be
unchanged, and the function shall return a value of -1 and set
errno
to indicate the error.
ERRORS
The
sem_trywait()
function shall fail if:
- EAGAIN
-
The semaphore was already locked, so it cannot be immediately locked by
the
sem_trywait()
operation.
The
sem_trywait()
and
sem_wait()
functions may fail if:
- EDEADLK
-
A deadlock condition was detected.
- EINTR
-
A signal interrupted this function.
- EINVAL
-
The
sem
argument does not refer to a valid semaphore.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Applications using these functions may be subject to priority inversion,
as discussed in the Base Definitions volume of POSIX.1-2017,
Section 3.291,
Priority Inversion.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
semctl(),
semget(),
semop(),
sem_post(),
sem_timedwait()
The Base Definitions volume of POSIX.1-2017,
Section 3.291, Priority Inversion,
Section 4.12, Memory Synchronization,
<semaphore.h>
COPYRIGHT
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 .
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 .