Wie implementiert PHP Multithread-Parallelität?

<?php 
if(function_exists(&#39;date_default_timezone_set&#39;)) { 
date_default_timezone_set(&#39;PRC&#39;); 
} 
function a() { 
$time = time(); sleep(3); 
$fp = fopen(&#39;result_a&#39;.$time.&#39;.log&#39;, &#39;w&#39;); 
fputs($fp, &#39;Set in &#39; . Date(&#39;h:i:s&#39;, time()) . (double)microtime() . "rn"); 
fclose($fp); 
} 
function b() { 
$time = time(); 
sleep(3); 
$fp = fopen(&#39;result_b&#39;.$time.&#39;.log&#39;, &#39;w&#39;); 
fputs($fp, &#39;Set in &#39; . Date(&#39;h:i:s&#39;, time()) . (double)microtime() . "rn"); 
fclose($fp); 
} 
if(!isset($_GET[&#39;act&#39;])) $_GET[&#39;act&#39;] = &#39;a&#39;; 
if($_GET[&#39;act&#39;] == &#39;a&#39;) { 
a(); 
} 
else if($_GET[&#39;act&#39;] == &#39;b&#39;) 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
Fixed a bug where :doc:`Image Manipulation Library <libraries/image_lib>` didn&#39;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&#39;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 &#39;oci8&#39; driver if there was no error.
Fixed a bug (#4647) - :doc:`Query Builder <database/query_builder>` method count_all_results() doesn&#39;t take into account GROUP BY clauses while deciding whether to do a subquery or not.
Fixed a bug where