php是如何实现多线程并发的

PHP 默认并不支持多线程，要使用多线程需要安装 pthread 扩展，而要安装 pthread 扩展，必须使用 --enable-maintainer-zts 参数重新编译 PHP，这个参数是指定编译 PHP 时使用线程安全方式。

<?php 
if(function_exists(\'date_default_timezone_set\')) { 
date_default_timezone_set(\'PRC\'); 
} 
function a() { 
$time = time(); sleep(3); 
$fp = fopen(\'result_a\'.$time.\'.log\', \'w\'); 
fputs($fp, \'Set in \' . Date(\'h:i:s\', time()) . (double)microtime() . "rn"); 
fclose($fp); 
} 
function b() { 
$time = time(); 
sleep(3); 
$fp = fopen(\'result_b\'.$time.\'.log\', \'w\'); 
fputs($fp, \'Set in \' . Date(\'h:i:s\', time()) . (double)microtime() . "rn"); 
fclose($fp); 
} 
if(!isset($_GET[\'act\'])) $_GET[\'act\'] = \'a\'; 
if($_GET[\'act\'] == \'a\') { 
a(); 
} 
else if($_GET[\'act\'] == \'b\') b(); 
?>

以上代码，在本地写入一个文件。

PHP多线程读写文件：

如果你访问 localhost/a.php 在两个浏览器标签尽可能快的同时打开，发现两个文件创建时间相差为3秒

但是如果你访问localhost/a.php?act=b 另一个访问/a.php?act=a 你发现两个文件创建的时间几乎差不多。

对于apache来说同样的url意味着一个线程（我们或者说是进程），但是不同的URL意味着可以并发。

如果php内部有下载的动作

function runThread() { 
down("http://localhost/test/a.php?act=a"); 
} 
if($_GET[\'act\'] == \'run\') { 
echo \'start:\'; 
runThread(); 
echo \' End\'; 
}

http://localhost/test/a.php?act=run

http://localhost/test/a.php?act=run&s=2

只要主访问的url不同，则认为是不同的进行，意味着并发。文件创建时间不为3秒

本地有Linux服务器的朋友也可以借助linux来进行模拟并发

1	`<?php` `for` `($i=0;$i<10;$i++) {` `echo` `$i; sleep(5); } ?>`

上面存成test.php, 然后写一段SHELL代码

#!/bin/bash
for i in 1 2 3 4 5 6 7 8 9 10
do
php -q test.php &
done
Fixed a bug where :doc:`Image Manipulation Library <libraries/image_lib>` didn\'t escape image source paths passed to ImageMagick as shell arguments.
Fixed a bug (#861) - :doc:`Database Forge <database/forge>` method create_table() incorrectly accepts field width constraints for mssql/SQLSRV integer-type columns.
Fixed a bug (#4562) - :doc:`Cache Library <libraries/caching>` didn\'t check if Memcached::quit() is available before calling it.
Fixed a bug (#4563) - :doc:`Input Library <libraries/input>` method request_headers() ignores $xss_clean parameter value after first call.
Fixed a bug (#4605) - :doc:`Config Library <libraries/config>` method site_url() stripped trailing slashes from relative URIs passed to it.
Fixed a bug (#4613) - :doc:`Email Library <libraries/config>` failed to send multiple emails via SMTP due to "already authenticated" errors when keep-alive is enabled.
Fixed a bug (#4633) - :doc:`Form Validation Library <libraries/form_validation>` ignored multiple "callback" rules for empty, non-required fields.
Fixed a bug (#4637) - :doc:`Database <database/index>` method error() returned FALSE with the \'oci8\' driver if there was no error.
Fixed a bug (#4647) - :doc:`Query Builder <database/query_builder>` method count_all_results() doesn\'t take into account GROUP BY clauses while deciding whether to do a subquery or not.
Fixed a bug where