Detailed explanation of php declare usage

php The general usage of declare is "declare(ticks=N);". Its function is that the Zend engine will execute the function registered by "register_tick_function()" every time it executes a low-level statement.

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Detailed explanation of the function of declare in php

The general usage is declare(ticks=N);

Take declare(ticks=1) as an example. This sentence has two main functions:

1. Every time the Zend engine When executing a low-level statement, the function registered by register_tick_function() is executed once.

It can be roughly understood that every time a sentence of php code is executed (for example: $num=1;), the registered tick function will be executed.

One use is to control the execution time of a certain piece of code. For example, although the following code has an infinite loop at the end, the execution time will not exceed 5 seconds.

Run php timeout.php

 $timeout ){ exit ( "超时{$timeout}秒\n" ); } } // Zend引擎每执行一次低级语句就执行一下check_timeout register_tick_function( 'check_timeout' ); // 模拟一段耗时的业务逻辑 while (1){ $num = 1; } // 模拟一段耗时的业务逻辑，虽然是死循环，但是执行时间不会超过$timeout=5秒 while (1){ $num = 1; }

2. declare(ticks=1); Each time a low-level statement is executed, the process will be checked for unhandled signals. , the test code is as follows:

Run php signal.php

Then CTL c or kill -SIGINT PID will cause the running code to jump out of the infinite loop to run the function registered by pcntl_signal. The effect is that the script exit prints " Get signal SIGINT and exi"Exit

        

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