Blocking Wait¶
A blocking wait, or blocking call, is an operation that suspends the execution of the current process or thread until the operation completes. During a blocking wait, no other work can be done by that execution unit.
Most PHP I/O operations like file reads, database queries, HTTP requests via curl… are blocking by default. The PHP process simply waits until the operation returns a result.
The alternative is non-blocking or asynchronous I/O, where execution continues and a callback or coroutine is invoked when the result is ready. Frameworks such as ReactPHP and Amp provide non-blocking event loops for PHP.
Blocking waits can become a bottleneck in high-concurrency scenarios, as each blocking call ties up a worker process.
<?php
// Blocking: execution stops here until the HTTP response arrives
$response = file_get_contents('https://api.example.com/data');
// Blocking: waits for the sleep to complete
sleep(2);
// Non-blocking alternative using ReactPHP
$loop = React\EventLoop\Factory::create();
$browser = new React\Http\Browser($loop);
$browser->get('https://api.example.com/data')->then(function ($response) {
echo $response->getBody();
});
$loop->run();
?>
See also Blocking vs non-blocking I/O.
Related : Async, Asynchronous, Synchronous, Fibers, Coroutine, Event Loop, Polling
Related packages : react/event-loop, amphp/amp
