Does php support multi-threading?

PHP does not support multi-threading by default. To use multi-threading, you need to install the pthread extension. To install the pthread extension, you must use the --enable-maintainer-zts parameter to recompile PHP. This parameter is specified when compiling PHP. Use thread safety.

Thread safety

Multi-threading is a factor that makes the program restless. Before using multi-threading , first of all, we must consider the issue of thread safety: (Recommended learning: PHP programming from entry to proficiency)

Thread safety: Thread safety is a term in programming, which refers to the use of a certain function or function library in When called in a multi-threaded environment, shared variables between multiple threads can be correctly processed so that program functions can be completed correctly.

In traditional multi-threading, since multiple threads share variables, the following problems may occur:

There is a global array $arr = array('a');;

A thread gets the array length to be 1;

B thread gets the array length to be 1;

A thread pops out the array element $a = array_pop($arr); $a = 'a';;

B thread also pops the array element $b = array_pop($arr); $a = null;;

At this time, a supernatural event occurred in B thread, obviously The array length is greater than 0, or nothing pops out;

PHP implementation

The thread safety implemented by PHP mainly uses the TSRM mechanism to isolate global variables and static variables. , copy global variables and static variables to each thread, and each thread uses a backup of the main thread, thus avoiding variable conflicts and thread safety issues.

PHP's multi-thread encapsulation ensures thread safety. Programmers no longer need to consider adding various locks to global variables to avoid read and write conflicts. It also reduces the chance of errors and makes the code written more secure.

But the result is that once the sub-thread starts running, the main thread can no longer adjust the running details of the sub-thread, and the thread loses the ability to transmit messages between threads through global variables to a certain extent. .

At the same time, after PHP turns on the thread safety option, there will be additional losses when using the TSRM mechanism to allocate and use variables. Therefore, in a PHP environment that does not require multi-threading, use the ZTS (non-thread safety) version of PHP. Just fine.

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