学步园

php的内置函数file_get_contents想必当初是为读取硬盘文件设计的，所以在读取文件内容时如果磁盘繁忙或准备数据慢，file_get_contents会进入忙等待，期许数据会飞快的到来，而不会等哪怕1ms。但是这个东东也允许用来读取http内容，而且等待数据的行为和读取文件一样，而等待http返回和等待磁盘准备数据在时间上可不是一个量级的，所以当file_get_contents用来读取http内容时就进入了秒级的忙等待，从而导致cpu飙升。不过貌似新版本的php修复了该问题，或者和某些编译项有关。

情景见下：
strace -rv -p <PHP进程ID> -o strace.log
cat strace.log
----------------------------------------------
0.000019 select(8, [7], [7], [], {15, 0}) = 1 (out [7], left {15, 0}) <0.000006>
0.000029 poll([{fd=7, events=POLLIN|POLLPRI}], 1, 0) = 0 <0.000004>
0.000018 gettimeofday({1340090123, 417745}, NULL) = 0 <0.000004>
0.000017 gettimeofday({1340090123, 417763}, NULL) = 0 <0.000005>
0.000019 gettimeofday({1340090123, 417781}, NULL) = 0 <0.000005>
0.000019 select(8, [7], [7], [], {15, 0}) = 1 (out [7], left {15, 0}) <0.000010>
0.000034 poll([{fd=7, events=POLLIN|POLLPRI}], 1, 0) = 0 <0.000005>
0.000018 gettimeofday({1340090123, 417853}, NULL) = 0 <0.000005>
0.000018 gettimeofday({1340090123, 417871}, NULL) = 0 <0.000005>
0.000019 gettimeofday({1340090123, 417889}, NULL) = 0 <0.000005>
0.000019 select(8, [7], [7], [], {15, 0}) = 1 (out [7], left {15, 0}) <0.000006>
0.000028 poll([{fd=7, events=POLLIN|POLLPRI}], 1, 0) = 0 <0.000005>
0.000018 gettimeofday({1340090123, 417956}, NULL) = 0 <0.000007>
0.000020 gettimeofday({1340090123, 417974}, NULL) = 0 <0.000005>
0.000018 gettimeofday({1340090123, 417993}, NULL) = 0 <0.000004>
0.000032 select(8, [7], [7], [], {15, 0}) = 1 (out [7], left {15, 0}) <0.000006>
0.000036 poll([{fd=7, events=POLLIN|POLLPRI}], 1, 0) = 0 <0.000005>
0.000019 gettimeofday({1340090123, 418080}, NULL) = 0 <0.000005>
0.000018 gettimeofday({1340090123, 418097}, NULL) = 0 <0.000005>
0.000020 gettimeofday({1340090123, 418117}, NULL) = 0 <0.000005>
... ...
----------------------------------------------
php进入了持续数秒的非阻塞poll循环，直到数据返回，cpu使用率在此期间会飙升。

对于读取http内容，最好避免用file_get_contents，可以改用下面的自定义函数取代：

function url_get_contents($strUrl, $boolUseCookie=false)
{
	$ch = curl_init($strUrl);
	curl_setopt($ch, CURLOPT_HEADER, 0);
	curl_setopt($ch, CURLOPT_TIMEOUT, 5);
	curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
	curl_setopt($ch, CURLOPT_HTTPGET, true); 
	curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
	curl_setopt($ch, CURLOPT_REFERER, $_SERVER['HTTP_REFERER']); 
	curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
	curl_setopt($ch, CURLOPT_MAXREDIRS, 3);
	if ($boolUseCookie && is_array($_COOKIE) && count($_COOKIE) > 0) {
		$cookie_str = '';
		foreach($_COOKIE as $key => $value) {
			$cookie_str .= "$key=$value; "; 
		}
		curl_setopt($ch, CURLOPT_COOKIE, $cookie_str);
	}
	$response = curl_exec($ch);
	if (curl_errno($ch) != 0) {
		return false;
	}
	curl_close($ch);
	return $response;	
}