English
English
In modern backend development, multithreading has become a key technique for improving system concurrency. However, PHP—a popular backend language—does not natively support multithreading. This often puzzles beginners and even experienced developers. This article explores the reasons from the perspectives of design philosophy, technical constraints, and viable alternatives.
PHP was originally designed for web development with a core focus on handling individual HTTP requests quickly and efficiently. To ensure stability and resource isolation, PHP adopted a per-request execution model. This model avoids the complex problems of state sharing, such as session consistency, data races, and thread safety.
Although multithreading can boost an application’s concurrency, it also brings a host of difficult debugging and maintenance issues, including deadlocks, race conditions, and thread synchronization. For most request-based web applications, introducing multithreading not only brings minimal performance gains but also increases the risk of system errors.
PHP typically runs with a short-lived request-response lifecycle, meaning that each request is destroyed after completion and does not occupy long-term resources. In contrast, multithreaded programs must manage multiple active threads within a single process, demanding more from the server’s memory and resource management—an approach that does not align with PHP’s lightweight execution model.
Even though PHP lacks native multithreading capabilities, developers can still achieve concurrency using other methods. Here are two mainstream approaches:
By creating child processes, PHP can simulate concurrent execution. This can be done using the pcntl extension for process control:
if (function_exists('pcntl_fork')) {
$pid = pcntl_fork();
if ($pid == -1) {
die('could not fork');
} elseif ($pid) {
// Parent process code
} else {
// Child process code
}
}This method allows parallel task processing, but developers must carefully manage the lifecycle and resources of each child process.
Modern PHP ecosystems have introduced extensions and frameworks that support asynchronous programming, such as ReactPHP and Swoole. These use event-driven mechanisms to handle high-concurrency I/O operations within a single thread—ideal for scenarios with many simultaneous network requests.
For instance, Swoole leverages built-in coroutines to allow PHP to handle asynchronous tasks efficiently, much like Node.js, while keeping code readable and structured in a synchronous style.
The primary reason PHP does not support multithreading lies in its web-optimized execution model, which sacrifices complexity for development efficiency and stability. Even without native multithreading, developers can still achieve concurrency through methods like fork and asynchronous programming. Understanding these design choices helps developers make better technical decisions in real-world projects.
