sem_init

Name

sem_init
- initialize an unnamed semaphore

Library

libpthread.lib

Synopsis

#include <semaphore.h>

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

Return values

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

Detailed description

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 The sem argument is no longer valid after a successful call to sem_destroy.

Examples

sem_t psem;   
if (sem_init(&psem, 0, 1) < 0) {
        perror("sem_init");
        return -1;
   }

Limitation

Semaphore can be used only within the process, semaphore across the processes is not supported

Errors

The sem_init function will fail if:

[`ENOSYS`]
	the value of the pshared is not 0.
[`EINVAL`]
	The value argument exceeds `SEM_VALUE_MAX`.
[`ENOSPC`]
	Memory allocation error.

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