SEM_INIT(3)

NAME
sem_init - initialize an unnamed semaphore

LIBRARY
libpthread

SYNOPSIS
#include <semaphore.h>
int
sem_init(sem_t *sem, int pshared, unsigned int value);

DESCRIPTION
The sem_init() function initializes the unnamed semaphore pointed to by sem to have the value value. A non-zero value for pshared specifies a shared semaphore that can be used by multiple processes in addition to threads. Any process able to access the related backing memory, typically via fork(), is allowed to use a semaphore created with a non-zero pshared, otherwise only threads may access the semaphore.

Following a successful call to sem_init(), sem can be used as an argument in subsequent calls to sem_wait, sem_trywait, sem_post, and sem_destroy. sem is no longer valid after a successful call to sem_destroy.

IMPLEMENTATION NOTES
Shared sempahores are allocated out of anonymous shared mmapped pages. Due to lack of clarity in the standard the mechanics of destroying such a space are unclear, so sem_destroy is currently unable to reclaim such semaphores.

RETURN VALUES

ERRORS
sem_init() will fail if:

[EINVAL]
    value exceeds SEM_VALUE_MAX.

[ENOSPC]
    Memory allocation error.

SEE ALSO
umtx(2), sem_destroy(3), sem_post(3), sem_trywait(3), sem_wait(3)

STANDARDS
sem_init() conforms to p1003.1-96.