NAME

sem_init — initialize an unnamed semaphore

LIBRARY

Standard C Library (libc, -lc)

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, the semaphore should be located in shared memory region (see mmap(2), shm_open(2), and shmget(2)), any process having read and write access to address sem can perform semaphore operations on sem.

Following a successful call to sem_init(), sem can be used as an argument in subsequent calls to sem_wait(3), sem_trywait(3), sem_post(3), and sem_destroy(3). The sem argument is no longer valid after a successful call to sem_destroy(3).

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.

ERRORS

The sem_init() function will fail if:

[EINVAL]

The value argument exceeds SEM_VALUE_MAX.

[ENOSPC]

Memory allocation error.

SEE ALSO

sem_destroy(3), sem_getvalue(3), sem_post(3), sem_trywait(3), sem_wait(3)

STANDARDS

The sem_init() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).