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

<?php
declare (ticks=1);
// 开始时间
$time_start  = time();
// 检查是否已经超时
function  check_timeout(){
     // 开始时间
     global  $time_start ;
     // 5秒超时
     $timeout  = 5;
     if (time()- $time_start  >  $timeout ){
         exit ( "超时{$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( &#39;check_timeout&#39; );
// 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

<?php
declare (ticks=1);
pcntl_signal(SIGINT,  function (){
    exit ( "Get signal SIGINT and exit\n" );
});
echo  "Ctl + c or run cmd : kill -SIGINT "  . posix_getpid().  "\n"  ;
while (1){
   $num  = 1;
}

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