sem_init man page

Prolog

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

sem_init — initialize an unnamed semaphore

Synopsis

#include <semaphore.h>

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

Description

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

Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(), sem_timedwait(), sem_trywait(), sem_post(), and sem_destroy() is undefined.

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(), sem_timedwait(), sem_trywait(), sem_post(), and sem_destroy() operations. The use of the semaphore by threads other than those created in the same process is undefined.

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

Return Value

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

Errors

The sem_init() function shall fail if:

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

The following sections are informative.

See Also

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

The Base Definitions volume of POSIX.1‐2008, <semaphore.h>

Info

2013 IEEE/The Open Group POSIX Programmer's Manual