SEM_INIT
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
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or the interface may not be implemented on Linux.
NAME
sem_init
--- initialize an unnamed semaphore
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.
Following a successful call to
sem_init(),
the semaphore may be used in subsequent calls to
sem_wait(),
sem_timedwait(),
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_timedwait(),
sem_trywait(),
sem_post(),
and
sem_destroy()
operations.
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 performing
sem_wait(),
sem_timedwait(),
sem_trywait(),
sem_post(),
and
sem_destroy()
operations.
See
Section 2.9.9, Synchronization Object Copies and Alternative Mappings
for further requirements.
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
and return 0. 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 appropriate privileges to initialize the
semaphore.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
sem_destroy(),
sem_post(),
sem_timedwait(),
sem_trywait()
The Base Definitions volume of POSIX.1-2017,
<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 .
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