PHP进程–CPU100%与file_get_contents函数的关系

有时候，运行 Nginx、PHP-CGI(php-fpm) Web服务的 Linux 服务器，突然系统负载上升，使用 top 命令查看，很多 php-cgi 进程 CPU 使用率接近100%.后来，我通过跟踪发现，这类情况的出现，跟 PHP 的 file_get_contents() 函数有着密切的关系.一般网站中,基于命令行的php脚本来做采集任务是家常便饭,PHP程序员们喜欢使用简单便捷的 file_get_contents(“http://www.xxx.com/”)函数,来获取一个URL 的返回内容,但是,如果 http://example.com/ 这个网站响应缓慢，file_get_contents() 就会一直卡在那儿,不会超时.

要做到彻底解决，只能让 PHP 程序员们改掉直接使用 file_get_contents(“http://example.com/”) 的习惯，而是稍微修改一下，加个超时时间，用以下方式来实现 HTTP GET 请求。要是觉得麻烦，可以自行将以下代码封装成一个函数

<?php  
    $ctx = stream_context_create(array(  
       'http' => array(  
           'timeout' => 2 //设置一个超时时间，单位为秒  
           )  
       )  
    );  
    file_get_contents("http://example.com/", 0, $ctx);  

也可以这样做：

直接在php.ini中修改  default_socket_timeout =2

或ini_set(‘default_socket_timeout’,2); 

或者用curl代替：

function new_file_get_contents($url){
	$result = '';    	
    $ch = curl_init();
    $options = array(
    	CURLOPT_URL => $url,
    	CURLOPT_CONNECTTIMEOUT => 10,	//连接超时
    	CURLOPT_TIMEOUT => 10,			//接收数据时超时设置
    	CURLOPT_RETURNTRANSFER => true,
    	CURLOPT_POST => $method == 'post' ? 1 : 0,
    	CURLOPT_USERAGENT => 'Mozilla/5.0 (Windows NT 5.1; rv:5.0) Gecko/20100101 Firefox/5.0'
    );
    curl_setopt_array($ch, $options);
    $result = curl_exec($ch);
    curl_close($ch);
    	    
    return $result;
}

当然,导致php进程CPU100%的原因不只有这一种,那么,怎么确定是file_get_contents()函数导致的呢？首先,使用top命令查看CPU使用率较高的php进程.

找其中一个CPU100%的php进程的 PID，用以下命令跟踪一下：

strace -p xxxxx

如果屏幕显示：

select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})
poll([{fd=5, events=POLLIN}], 1, 0)     = 0 (Timeout)
select(6, [5], [5], [], {15, 0})        = 1 (out [5], left {15, 0})

那么,就可以确定是file_get_contents()导致的问题了

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