Section: Linux Programmer's Manual (3)
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sem_init - initialize an unnamed semaphore
int sem_init(sem_t *sem, int pshared, unsigned int value);
Link with -pthread.
initializes the unnamed semaphore at the address pointed to by
argument specifies the initial value for the semaphore.
argument indicates whether this semaphore is to be shared
between the threads of a process, or between processes.
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
is nonzero, then the semaphore is shared between processes,
and should be located in a region of shared memory (see
(Since a child created by
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
and so on.
Initializing a semaphore that has already been initialized
results in undefined behavior.
returns 0 on success;
on error, -1 is returned, and
is set to indicate the error.
but the system does not support process-shared semaphores (see
Multithreading (see pthreads(7))
function is thread-safe.
Bizarrely, POSIX.1-2001 does not specify the value that should
be returned by a successful call to
POSIX.1-2008 rectifies this, specifying the zero return on success.
This page is part of release 3.74 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
- RETURN VALUE
- Multithreading (see pthreads(7))
- CONFORMING TO
- SEE ALSO