The difference between synchronous programming and asynchronous programming
Before discussing the advantages of asynchronous PHP, let’s quickly review the synchronous programming model and asynchronous programming models. Synchronous code is executed sequentially, line by line. You must
complete the previous task before you can start another task. In asynchronous code, multiple tasks can be completed simultaneously, which can greatly improve application performance and user experience.
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##What is synchronous PHP?
Synchronous PHP refers to PHP code written using the synchronous model. PHP was originally created to support synchronous development, so most PHP developers are used to writing synchronous code in this language. Prefork using Apache's mod_php or php-fpm using Apache or Nginx.
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What is asynchronous PHP?
Asynchronous PHP refers to PHP code written using the asynchronous model. By using an extension like Swoole, or a PHP framework like ReactPHP, you can make PHP accept requests and responses asynchronously using an event loop.
What are the main differences between synchronous and asynchronous PHP programming?
In many applications, the CPU spends a lot of time idle during I/O tasks. The idea of asynchronous PHP is to make full use of all available CPU cycles to perform other tasks by having non-blocking I/O tasks run in the background, processing other tasks while the CPU waits for the data and instructions required to complete the I/O. Synchronous PHP, the CPU will only handle I/O tasks. After the current task is completed, continue processing the next task in the queue.
Use asynchronous PHP to achieve lightning-fast performance compared to applications written in synchronous PHP. In some benchmarks, using Swoole to enable asynchronous PHP can increase throughput by 100 times compared to using a process accelerator like php-fpm in synchronous code. This is why php-fpm does not support asynchronous real-time communication using protocols like Websockets.
Which PHP should you use?
As with most issues regarding runtime, web servers, and programming in general, different use cases will dictate whether to use synchronous or asynchronous PHP. To use asynchronous PHP, your code must support it. Most extensions that PHP developers are accustomed to use block process calls (also known as I/O blocking), which makes the asynchronous model unachievable.
For example, to utilize Swoole, when it encounters an I/O request call, it needs to send the call to the background and then continue to execute the next instruction. When the I/O call returns data, Swoole needs to return control to the I/O call that has been sent to the background so that it can control the request data to the process. Rewriting your code to support asynchronous processes may require some refactoring to work. However, the time you save may be worth it in the future.
Starting an Asynchronous PHP Project
Since you write code in a way that supports asynchronous processes, you must leverage a project that can do so. Here are our top three recommendations:
- Swoole – Collaborative PHP asynchronous programming framework.
- Reactphp – Event-driven, non-blocking I/O for PHP.
- Amphp – PHP non-blocking concurrency framework.
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