SEM_INIT(P) POSIX Programmer's Manual SEM_INIT(P)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.
NAMEsem_init - initialize an unnamed semaphore (REALTIME)
SYNOPSIS
#include <semaphore.h>
int sem_init(sem_t *sem, int pshared, unsigned value);
DESCRIPTION
The sem_init() function shall initialize the unnamed semaphore referred
to by sem. The value of the initialized semaphore shall be value. Fol‐
lowing a successful call to sem_init(), the semaphore may be used in
subsequent calls to sem_wait(), sem_trywait(), sem_post(), and
sem_destroy(). This semaphore shall remain usable until the semaphore
is destroyed.
If the pshared argument has a non-zero value, then the semaphore is
shared between processes; in this case, any process that can access the
semaphore sem can use sem for performing sem_wait(), sem_trywait(),
sem_post(), and sem_destroy() operations.
Only sem itself may be used for performing synchronization. The result
of referring to copies of sem in calls to sem_wait(), sem_trywait(),
sem_post(), and sem_destroy() is undefined.
If the pshared argument is zero, then the semaphore is shared between
threads of the process; any thread in this process can use sem for per‐
forming sem_wait(), sem_trywait(), sem_post(), and sem_destroy() opera‐
tions. The use of the semaphore by threads other than those created in
the same process is undefined.
Attempting to initialize an already initialized semaphore results in
undefined behavior.
RETURN VALUE
Upon successful completion, the sem_init() function shall initialize
the semaphore in sem. Otherwise, it shall return -1 and set errno to
indicate the error.
ERRORS
The sem_init() function shall fail if:
EINVAL The value argument exceeds {SEM_VALUE_MAX}.
ENOSPC A resource required to initialize the semaphore has been
exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has
been reached.
EPERM The process lacks the appropriate privileges to initialize the
semaphore.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The sem_init() function is part of the Semaphores option and need not
be available on all implementations.
RATIONALE
Although this volume of IEEE Std 1003.1-2001 fails to specify a suc‐
cessful return value, it is likely that a later version may require the
implementation to return a value of zero if the call to sem_init() is
successful.
FUTURE DIRECTIONS
None.
SEE ALSOsem_destroy() , sem_post() , sem_timedwait() , sem_trywait() ,
sem_wait() , the Base Definitions volume of IEEE Std 1003.1-2001, <sem‐
aphore.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 SEM_INIT(P)
