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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SEM_INIT(3) Linux Programmer's Manual SEM_INIT(3)
sem_init - initialize an unnamed semaphore
#include <semaphore.h>
int sem_init(sem_t *sem, int pshared, unsigned int value);
Link with -pthread.
sem_init() initializes the unnamed semaphore at the address pointed
to by sem. The value argument specifies the initial value for the
semaphore.
The pshared argument indicates whether this semaphore is to be shared
between the threads of a process, or between processes.
If pshared has the value 0, then the semaphore is shared between the
threads of a process, and should be located at some address that is
visible to all threads (e.g., a global variable, or a variable
allocated dynamically on the heap).
If pshared is nonzero, then the semaphore is shared between
processes, and should be located in a region of shared memory (see
shm_open(3), mmap(2), and shmget(2)). (Since a child created by
fork(2) inherits its parent's memory mappings, it can also access the
semaphore.) Any process that can access the shared memory region can
operate on the semaphore using sem_post(3), sem_wait(3), and so on.
Initializing a semaphore that has already been initialized results in
undefined behavior.
sem_init() returns 0 on success; on error, -1 is returned, and errno
is set to indicate the error.
EINVAL value exceeds SEM_VALUE_MAX.
ENOSYS pshared is nonzero, but the system does not support process-
shared semaphores (see sem_overview(7)).
For an explanation of the terms used in this section, see
attributes(7).
┌───────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────┼───────────────┼─────────┤
│sem_init() │ Thread safety │ MT-Safe │
└───────────┴───────────────┴─────────┘
POSIX.1-2001.
Bizarrely, POSIX.1-2001 does not specify the value that should be
returned by a successful call to sem_init(). POSIX.1-2008 rectifies
this, specifying the zero return on success.
sem_destroy(3), sem_post(3), sem_wait(3), sem_overview(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2015-03-02 SEM_INIT(3)
Pages that refer to this page: sem_destroy(3), sem_overview(7)