PHP在很多时候不适合做常驻的SHELL进程, 他没有专门的gc例程, 也没有有效的内存管理途径. 所以如果用PHP做常驻SHELL, 你会经常被内存耗尽导致abort而unhappy. 而且, 如果输入数据非法, 而脚本没有检测, 导致abort, 也会让你很不开心. 那? 怎么办呢? 多进程…. **为什么呢?** ~~~  优点:    1. 使用多进程, 子进程结束以后, 内核会负责回收资源    2. 使用多进程,子进程异常退出不会导致整个进程Thread退出. 父进程还有机会重建流程.    3. 一个常驻主进程, 只负责任务分发, 逻辑更清楚. ~~~ **Then, 怎么做呢?** 接下来, 我们使用PHP提供的POSIX和Pcntl系列函数, 来实现一个PHP命令解析器, 主进程负责接受用户输入, 然后fork子进程执行, 并负责回显子进程的结束状态. 代码如下, 我加了注释, 如果有不懂的地方, 可以翻阅手册相关函数, 或者[回复](http://www.laruence.com/2009/06/11/930.html#comment "风雪之隅")留言. ~~~ #!/bin/env php<?php/** A example denoted muti-process application in php * @filename fork.php * @touch date Wed 10 Jun 2009 10:25:51 PM CST * @author Laruence<laruence@baidu.com> * @license http://www.zend.com/license/3_0.txt PHP License 3.0 * @version 1.0.0*/ /** 确保这个函数只能运行在SHELL中 */if (substr(php_sapi_name(), 0, 3) !== 'cli') {    die("This Programe can only be run in CLI mode");} /** 关闭最大执行时间限制, 在CLI模式下, 这个语句其实不必要 */set_time_limit(0); $pid = posix_getpid(); //取得主进程ID$user = posix_getlogin(); //取得用户名 echo <<<eodUSAGE: [command | expression]input php code to execute by fork a new processinput quit to exit         Shell Executor version 1.0.0 by laruenceEOD; while (true) {         $prompt = "\n{$user}$ ";        $input = readline($prompt);         readline_add_history($input);        if ($input == 'quit') {               break;          }        process_execute($input . ';');} exit(0); function process_execute($input) {        $pid = pcntl_fork(); //创建子进程        if ($pid == 0) {//子进程                $pid = posix_getpid();                echo "* Process {$pid} was created, and Executed:\n\n";                eval($input); //解析命令                exit;        } else {//主进程                $pid = pcntl_wait($status, WUNTRACED); //取得子进程结束状态                if (pcntl_wifexited($status)) {                        echo "\n\n* Sub process: {$pid} exited with {$status}";                }        }}   ~~~ 但有一点, 我一定要提醒: ~~~ Process Control should not be enabled within a webserver environment and unexpected results may happen if any Process Control functions are used within a webserver environment. --摘自PHP手册 ~~~ **也就是说, 打消你在PHP Web开发中使用多进程的念头吧!** http://www.laruence.com/2009/06/11/930.html