NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | 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 -lrt or -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 non-zero, 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), etc.
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 non-zero, but the system does not support process-shared
semaphores (see sem_overview(7)).
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 3.23 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-07-27 SEM_INIT(3)