SEM_INIT(3) Linux Programmer's Manual SEM_INIT(3)
sem_init - initialize an unnamed semaphore
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 vari-
able, 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 sema-
phore 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
EINVAL value exceeds SEM_VALUE_MAX.
ENOSYS pshared is nonzero, 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 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)
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Linux 2012-05-13 SEM_INIT(3)