sem_init (3)
Leading comments
Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. ...
NAME
sem_init - initialize an unnamed semaphoreSYNOPSIS
#include <semaphore.h> int sem_init(sem_t *sem, int pshared, unsigned int value);
Link with -pthread.
DESCRIPTION
sem_init() initializes the unnamed semaphore at the address pointed to by sem. The value argument specifies the initial value for the semaphore.The pshared argument indicates whether this semaphore is to be shared between the threads of a process, or between processes.
If pshared has the value 0, then the semaphore is shared between the threads of a process, and should be located at some address that is visible to all threads (e.g., a global variable, or a variable allocated dynamically on the heap).
If pshared is nonzero, then the semaphore is shared between processes, and should be located in a region of shared memory (see shm_open(3), mmap(2), and shmget(2)). (Since a child created by fork(2) inherits its parent's memory mappings, it can also access the semaphore.) Any process that can access the shared memory region can operate on the semaphore using sem_post(3), sem_wait(3), and so on.
Initializing a semaphore that has already been initialized results in undefined behavior.
RETURN VALUE
sem_init() returns 0 on success; on error, -1 is returned, and errno is set to indicate the error.ERRORS
- EINVAL
- value exceeds SEM_VALUE_MAX.
- ENOSYS
- pshared is nonzero, but the system does not support process-shared semaphores (see sem_overview(7)).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| sem_init() | Thread safety | MT-Safe |