转载请注明原文链接：http://blog.s135.com/file_get_contents/]
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。
大、中型网站中，基于 HTTP 协议的 API 接口调用，是家常便饭。PHP 程序员们喜欢使用简单便捷的 file_get_contents("http://example.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。
我们知道，在 php.ini 中，有一个参数 max_execution_time 可以设置 PHP 脚本的最大执行时间，但是，在 php-cgi(php-fpm) 中，该参数不会起效。真正能够控制 PHP 脚本最大执行时间的是 php-fpm.conf 配置文件中的以下参数：
- The timeout (in seconds) for serving a single request after which the worker process will be terminated
- Should be used when 'max_execution_time' ini option does not stop script execution for some reason
- '0s' means 'off'
- <value name="request_terminate_timeout">0s</value>
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' => 1 //设置一个超时时间，单位为秒
- )
- )
- );
- file_get_contents("http://example.com/", 0, $ctx);
- ?>
首先，使用 top 命令查看 CPU 使用率较高的 php-cgi 进程。
top - 10:34:18 up 724 days, 21:01, 3 users, load average: 17.86, 11.16, 7.69
Tasks: 561 total, 15 running, 546 sleeping, 0 stopped, 0 zombie
Cpu(s): 5.9%us, 4.2%sy, 0.0%ni, 89.4%id, 0.2%wa, 0.0%hi, 0.2%si, 0.0%st
Mem: 8100996k total, 4320108k used, 3780888k free, 772572k buffers
Swap: 8193108k total, 50776k used, 8142332k free, 412088k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10747 www 18 0 360m 22m 12m R 100.6 0.3 0:02.60 php-cgi
10709 www 16 0 359m 28m 17m R 96.8 0.4 0:11.34 php-cgi
10745 www 18 0 360m 24m 14m R 94.8 0.3 0:39.51 php-cgi
10707 www 18 0 360m 25m 14m S 77.4 0.3 0:33.48 php-cgi
10782 www 20 0 360m 26m 15m R 75.5 0.3 0:10.93 php-cgi
10708 www 25 0 360m 22m 12m R 69.7 0.3 0:45.16 php-cgi
10683 www 25 0 362m 28m 15m R 54.2 0.4 0:32.65 php-cgi
10711 www 25 0 360m 25m 15m R 52.2 0.3 0:44.25 php-cgi
10688 www 25 0 359m 25m 15m R 38.7 0.3 0:10.44 php-cgi
10719 www 25 0 360m 26m 16m R 7.7 0.3 0:40.59 php-cgi
Tasks: 561 total, 15 running, 546 sleeping, 0 stopped, 0 zombie
Cpu(s): 5.9%us, 4.2%sy, 0.0%ni, 89.4%id, 0.2%wa, 0.0%hi, 0.2%si, 0.0%st
Mem: 8100996k total, 4320108k used, 3780888k free, 772572k buffers
Swap: 8193108k total, 50776k used, 8142332k free, 412088k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
10747 www 18 0 360m 22m 12m R 100.6 0.3 0:02.60 php-cgi
10709 www 16 0 359m 28m 17m R 96.8 0.4 0:11.34 php-cgi
10745 www 18 0 360m 24m 14m R 94.8 0.3 0:39.51 php-cgi
10707 www 18 0 360m 25m 14m S 77.4 0.3 0:33.48 php-cgi
10782 www 20 0 360m 26m 15m R 75.5 0.3 0:10.93 php-cgi
10708 www 25 0 360m 22m 12m R 69.7 0.3 0:45.16 php-cgi
10683 www 25 0 362m 28m 15m R 54.2 0.4 0:32.65 php-cgi
10711 www 25 0 360m 25m 15m R 52.2 0.3 0:44.25 php-cgi
10688 www 25 0 359m 25m 15m R 38.7 0.3 0:10.44 php-cgi
10719 www 25 0 360m 26m 16m R 7.7 0.3 0:40.59 php-cgi
找其中一个 CPU 100% 的 php-cgi 进程的 PID，用以下命令跟踪一下：
strace -p 10747
如果屏幕显示：
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
select(7, [6], [6], [], {15, 0}) = 1 (out [6], left {15, 0})
poll([{fd=6, events=POLLIN}], 1, 0) = 0 (Timeout)
那么，就可以确定是 file_get_contents() 导致的问题了。
