Mutex¶

A mutex, a mutual exclusion, is a synchronization primitive that prevents multiple processes or threads from accessing a shared resource simultaneously. Only one holder can acquire the mutex at a time; all others must wait until it is released.

Thread-level mutexes are provided by the parallel extension. For process-level mutual exclusion, e.g., preventing concurrent cron runs, the standard approach is file-based locking with flock().

<?php

    // Process-level mutex with flock()
    $lock = fopen('/tmp/my_job.lock', 'c');

    if (!flock($lock, LOCK_EX | LOCK_NB)) {
        // Another process already holds the lock
        fclose($lock);
        exit(0);
    }

    try {
        // Critical section: only one process runs this at a time
        doExpensiveWork();
    } finally {
        flock($lock, LOCK_UN);
        fclose($lock);
    }

?>

Documentation

Mutex¶

PHP Dictionary

Navigation

Related Topics