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SEM_INIT(3) Library Functions Manual SEM_INIT(3)

sem_initinitialize an unnamed semaphore

#include <semaphore.h>

sem_init(sem_t *sem, int pshared, unsigned int value);

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 sem is no longer valid after a successful call to sem_destroy(3).

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.

It is an error to call sem_destroy(3) on a named semaphore created by sem_open(3).

sem_init() will fail if:

value exceeds SEM_VALUE_MAX.
Memory allocation error.
Unable to initialize a shared semaphore.

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

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.

February 11, 2023 OpenBSD-current