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Name

Synopsis

#include <semaphore.h>
int sem_init(sem_t *sem, int pshared, unsigned int value);

Link with -pthread.

Description

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

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

Multithreading (see pthreads(7) )

Conforming to

Notes

See Also

Colophon

Table of Contents

• Name
• Synopsis
• Description
• Return Value
• Errors
• Attributes
• Multithreading (see pthreads(7))
• Conforming to
• Notes
• See Also
• Colophon