Section: Linux Programmer's Manual (3)
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sem_init - initialise an unnamed semaphore
int sem_init(sem_t *sem, int pshared, unsigned int value);
initialises 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 non-zero, 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
Initialising a semaphore that has already been initialised
results in undefined behaviour.
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
Bizarrely, POSIX.1-2001 does not specify the value that should
be returned by a successful call to
However, virtually every implementation returns zero in this case.
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
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