SEM_TRYWAIT(3P) POSIX Programmer's Manual SEM_TRYWAIT(3P)PROLOG
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 sema‐
phore 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 sema‐
phore 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 inver‐
sion, as discussed in the Base Definitions volume of POSIX.1‐2008, Sec‐
tion 3.287, Priority Inversion.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOsemctl(), semget(), semop(), sem_post(), sem_timedwait()
The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority
Inversion, Section 4.11, Memory Synchronization, <semaphore.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal 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 Standard
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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 SEM_TRYWAIT(3P)
