SEM_INIT(3) Library Functions Manual SEM_INIT(3)

sem_init — initialize an unnamed semaphore

#include <semaphore.h>

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

The sem_init () function shall initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore shall be . Following a successful call to sem_init (), the semaphore may be used in subsequent calls to sem_wait(3), sem_timedwait(3), sem_trywait(3), sem_post(3), and sem_destroy(3). This semaphore shall remain usable until the semaphore is destroyed.

If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore sem can use sem for performing sem_wait(3), sem_timedwait(3), sem_trywait(3), sem_post(3), and sem_destroy(3) operations.

If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can use sem for performing sem_wait(3), sem_timedwait(3), sem_trywait(3), sem_post(3), and sem_destroy(3) operations.

See V2_chap02(3) for further requirements.

Attempting to initialize an already initialized semaphore results in undefined behavior.

Upon successful completion, the sem_init () function shall initialize the semaphore in sem and return 0. Otherwise, it shall return -1 and set to indicate the error.

The sem_init () function shall fail if:

The value argument exceeds {SEM_VALUE_MAX}.
A resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has been reached.
The process lacks appropriate privileges to initialize the semaphore.

None.

None.

None.

None.

sem_destroy(3), sem_post(3), sem_timedwait(3), sem_trywait(3)

XBD <semaphore.h>

First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

The sem_init () function is marked as part of the Semaphores option.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Semaphores option.

The sem_timedwait(3) function is added to the SEE ALSO section for alignment with IEEE Std 1003.1d-1999.

IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/116 is applied, updating the DESCRIPTION to add the sem_timedwait(3) function for alignment with IEEE Std 1003.1d-1999.

SD5-XSH-ERN-176 is applied.

The sem_init () function is moved from the Semaphores option to the Base.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0526 [37] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0318 [972] is applied.

January 31, 2018 posix.fail