Is php multi-threaded or single-threaded?

From the beginning of PHP's design to its popularity, there has been no obvious need to use multi-threading to solve it.

There are also corresponding solutions and alternatives where multi-threading is required. Multi-threading is not always better than single-threading. Multi-threading may introduce other problems (for example, a deadlock may occur when two threads call the same method in a class at the same time). (Recommended learning: PHP Programming from entry to proficiency)

You can understand that the PHP corresponding to a page request processing by a customer is processed by a single thread, so that it can be processed from top to bottom The next step is to edit/understand the business logic in the code, but PHP can open many threads at the same time to handle the same PHP requested by many users, so PHP can also be regarded as "multi-threaded".

The execution of each PHP file is single-threaded, however, the server (apache/nigix/php-fpm) is multi-threaded. Every time a certain PHP file is accessed by the server, a new process/thread will be created to execute the corresponding PHP file.

That is to say, PHP is single-threaded for one request, but multiple requests are concurrent.

In fact, generally when writing PHP programs, it is considered to be single-threaded. The relationship between multiple requests is that sometimes reading and writing databases, files, sessions, etc. will be locked, which will cause subsequent requests to hang and wait for the previous request to complete before continuing.

As for the coroutine, it can only be said to be a new program execution process (the old one is sequence, judgment, loop), and its essence is also single-threaded

So to be precise, PHP is single-threaded, and to a certain extent it can also be regarded as "multi-threaded"! ! !

PHP multi-threading

By default, PHP does not support multi-threading. To use multi-threading, you need to install an extension. Currently, commonly used extensions include pcnlt , POSIX, pthreads, but the most used one is the pthreads extension. It uses parameters to specify the thread-safe way when compiling PHP, so that it supports multi-threading.

Before using threads, you must first consider the thread Security issues, thread safety means that when a function or function library is called in a multi-threaded environment, it can correctly handle the shared variables between multiple threads, so that the function of the program can be completed correctly

PHP realizes thread safety

PHP realizes thread safety mainly through the TSRM mechanism. Through this mechanism, global variables and static variables can be isolated, and a copy of global variables and static variables can be copied to each thread. variable. Each thread uses a backup of the main thread. This avoids variable conflicts and does not cause thread safety issues.

PHP's encapsulation of multi-threading ensures thread safety, so developers do not need to consider read and write conflicts, which also makes the code safer. However, there are disadvantages to this. For example, when the sub-thread starts running, the main thread can no longer adjust the running details of the sub-thread and loses the ability to deliver messages

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