sem_init(3) Library Functions Manual sem_init(3)
NAME
sem_init - Initializes an unnamed semaphore (P1003.1b)
LIBRARY
Realtime Library (librt.so, librt.a)
SYNOPSIS
#include <semaphore.h>
int sem_init (
sem_t *sem,
int pshared,
unsigned int value);
PARAMETERS
sem Specifies a location to receive the descriptor of the initialized semaphore.
pshared Specifies a value indicating whether the semaphore should be sharable between processes (non-zero value) or not (zero).
value Specifies the initial value to be given to the semaphore.
DESCRIPTION
The sem_init function creates a new counting semaphore with a specific value. A semaphore is used to limit access to a critical resource.
When a process requires access to the resource without interference from other processes, it attempts to establish a connection with the
associated semaphore. If the semaphore value is greater than zero, the connection is established and the semaphore value is decremented by
one. If the semaphore value is less than or equal to zero, the process attempting to access the resource is blocked and must wait for
another process to release the semaphore and increment the semaphore value.
The sem_init function establishes a connection between an unnamed semaphore and a process; the sem_wait and sem_trywait functions lock the
semaphore; and the sem_post function unlocks the semaphore. Use the sem_destroy function to deallocate system resources allocated to the
process for use with the semaphore. You can use the sem_getvalue function to obtain the value of a semaphore.
A semaphore created by a call to the sem_init function remains valid until the semaphore is removed by a call to the sem_destroy function.
RETURN VALUES
On successful completion, the function returns the value 0 (zero); otherwise, the function returns the value -1 and sets errno to indicate
the error.
ERRORS
The sem_init function fails under the following conditions:
[EINVAL] The value argument exceeds {SEM_VALUE_MAX}.
[ENOSPC] A resource required to initialize the semaphore has been exhausted. The limit on semaphores ({SEM_NSEMS_MAX}) has been
reached.
[EPERM] The process lacks the appropriate privilege to initialize the semaphore.
RELATED INFORMATION
Functions: sem_destroy(3), sem_post(3), sem_trywait(3),sem_wait(3)
Guide to Realtime Programming delim off
sem_init(3)
