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sem_get

(PHP 4, PHP 5, PHP 7, PHP 8)

sem_get — Get a semaphore id

Description

sem_get(
    int $key,
    int $max_acquire = 1,
    int $permissions = 0666,
    bool $auto_release = true
): SysvSemaphore|false

sem_get() returns an id that can be used to access the System V semaphore with the given key.

A second call to sem_get() for the same key will return a different semaphore identifier, but both identifiers access the same underlying semaphore.

If key is 0, a new private semaphore is created for each call to sem_get().

Parameters

key
max_acquire
The number of processes that can acquire the semaphore simultaneously is set to max_acquire.
permissions
The semaphore permissions. Actually this value is set only if the process finds it is the only process currently attached to the semaphore.
auto_release
Specifies if the semaphore should be automatically released on request shutdown.

Return Values

Returns a positive semaphore identifier on success, or false on error.

Changelog

Version Description
8.0.0 On success, this function returns a SysvSemaphore instance now; previously, a resource was returned.
8.0.0 The type of auto_release has been changed from int to bool.

Notes

Warning

When using sem_get() to access a semaphore created outside PHP, note that the semaphore must have been created as a set of 3 semaphores (for example, by specifying 3 as the nsems parameter when calling the C semget() function), otherwise PHP will be unable to access the semaphore.

See Also