SEM_INIT(3) BSD Library Functions Manual SEM_INIT(3)NAMEsem_init — initialize an unnamed semaphore
LIBRARY
POSIX Threads Library (libpthread, -lpthread)
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, typi‐
cally 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sem is no longer valid after a successful call to sem_destroy.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
The sem_init() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORSsem_init() will fail if:
[EINVAL] value exceeds SEM_VALUE_MAX.
[ENOSPC] Memory allocation error.
SEE ALSOumtx(2), sem_destroy(3), sem_post(3), sem_trywait(3), sem_wait(3)STANDARDSsem_init() conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).
BSD June 30, 2009 BSD
