php多线程并发实现方法

<?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();
?>

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

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

#!/bin/bash
for i in 1 2 3 4 5 6 7 8 9 10
do
php -q test.php &
done