PHP单线程实现并行抓取网页
本PHP教程将模拟并行抓取多个页面信息的过程,关键在于单线程的并行处理。
一般情况下,大家写抓取多个页面信息的程序都采用串行方案,但获取周期过长,不实用。于是我想到用curl 去并行抓取。但是,最后发现,那个虚拟服务器上没有curl,这真是让人纠结。于是,我决定改变思路,用单个线程也实现多个线程的效果。我想对网络编程有点
了解的人肯定知道IO复用这个概念,当然PHP上也是支持的,而且,内部支持,不需要任何扩展。
可能有很多年编程经验的人对PHP的stream 函数可能不太了解。PHP的压缩文件流,文件流,tcp 协议下的应用 都封装成一个stream。所以,读本地文件
和读网络文件没有任何的差别。说了这样多,我想大家都基本上明白了,直接贴上代码吧:
代码比较的粗糙,如果大家要实际用的话,还是要处理一些细节问题。
代码
function http_get_open($url)
{
$url = parse_url($url);
if (empty($url['host'])) {
return false;
}
$host = $url['host'];
if (empty($url['path'])) {
$url['path'] = "/";
}
$get = $url['path'] . "?" . @$url['query'];
$fp = stream_socket_client("tcp://{$host}:80", $errno, $errstr, 30);
if (!$fp) {
echo "$errstr ($errno)
\n";
return false;
} else {
fwrite($fp, "GET {$get} HTTP/1.0\r\nHost: {$host}\r\nAccept: */*\r\n\r\n");
}
return $fp;
}
function http_multi_get($urls)
{
$result = array();
$fps = array();
foreach ($urls as $key => $url)
{
$fp = http_get_open($url);
if ($fp === false) {
$result[$key] = false;
} else {
$result[$key] = '';
$fps[$key] = $fp;
}
}
while (1)
{
$reads = $fps;
if (empty($reads)) {
break;
}
if (($num = stream_select($reads, $w = null, $e = null, 30)) === false ) {
echo "error";
return false;
} else if ($num > 0) {//can read
foreach ($reads as $value)
{
$key = array_search($value, $fps);
if (!feof($value)) {
$result[$key] .= fread($value, 128);
} else {
unset($fps[$key]);
}
}
} else {//time out
echo "timeout";
return false;
}
}
foreach ($result as $key => &$value)
{
if ($value) {
$value = explode("\r\n\r\n", $value, 2);
}
}
return $result;
}
$urls = array();
$urls[] = "http://www.qq.com";
$urls[] = "http://www.sina.com.cn";
$urls[] = "http://www.sohu.com";
$urls[] = "http://www.blue1000.com";
//并行的抓取
$t1 = microtime(true);
$result = http_multi_get($urls);
$t1 = microtime(true) - $t1;
var_dump("cost: " . $t1);
//串行的抓取
$t1 = microtime(true);
foreach ($urls as $value)
{
file_get_contents($value);
}
$t1 = microtime(true) - $t1;
var_dump("cost: " . $t1);
?>
最后运行的结果:
string 'cost: 3.2403128147125' (length=21)
string 'cost: 6.2333900928497' (length=21)
基本上是两倍的效率,当然,发现新浪非常的慢,要2.5s 左右,
基本上是被他给拖累了,360只要 0.2s
如果,所有网站都差不多的速度,并行的数目更大,那么差的倍数也就越大。

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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