NAME

sem_init — initialize an unnamed semaphore

LIBRARY

POSIX Real-time Library (librt, -lrt)

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, which this implementation is not capable of.

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 sem is no longer valid after a successful call to sem_destroy.

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

sem_init() will fail if:

[EINVAL]

value exceeds SEM_VALUE_MAX.

[ENOSPC]

Memory allocation error.

[EPERM]

Unable to initialize a shared semaphore.

SEE ALSO

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

STANDARDS

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

This implementation does not support shared semaphores, and reports this fact by setting errno to EPERM. This is perhaps a stretch of the intention of POSIX, but is compliant, with the caveat that sem_init() always reports a permissions error when an attempt to create a shared semaphore is made.