The Swoole\Coroutine\Lock class

Introduction

Swoole 6.0.1 introduced a coroutine lock that supports inter-process and inter-thread sharing. This lock is designed with non-blocking behavior and enables efficient coroutine synchronization in multi-process and multi-thread environments.

When compiled with the --enable-iouring option and the Linux kernel supports the io_uring futex feature, Swoole's coroutine lock implements synchronization using io_uring futex. In this case, coroutines wait for lock wakeups using an efficient queuing mechanism, significantly improving performance.

Without io_uring futex, the coroutine lock falls back to an exponential backoff sleep mechanism, where the wait time increases by 2^n milliseconds (n being the number of failures) after each failed attempt to acquire the lock. While this approach avoids busy waiting, it introduces additional CPU scheduling overhead and latency.

The coroutine lock is reentrant, allowing the currently holding coroutine to safely perform multiple lock operations.

Class synopsis

Examples

<?php
use Swoole\Coroutine\Lock;
use Swoole\Coroutine\WaitGroup;
use function Swoole\Coroutine\go;
use function Swoole\Coroutine\run;

$lock = new Lock();
$waitGroup = new WaitGroup();

run(function() use ($lock, $waitGroup) {
    go(function() use ($lock, $waitGroup) {
        $waitGroup->add();
        $lock->lock();
        sleep(1);
        $lock->unlock();
        $waitGroup->done();
    });

    go(function() use ($lock, $waitGroup) {
        $waitGroup->add();
        $lock->lock(); // Wait for the holding coroutine to unlock
        sleep(1);
        $lock->unlock();
        $waitGroup->done();
    });

    echo 'Lock does not block the process';
    $waitGroup->wait();
});