Question

所以，我有这个监听IPC消息的PHP守护进程工作者。奇怪的是父进程（来自pcntl_fork的结果）留下了[php]＆lt;被禁＆GT;进程，直到子进程完成，但仅当脚本从cronjob启动时，而不是直接从命令行启动。

我知道＆lt;被禁＆GT;进程并不邪恶，但我无法弄清楚为什么只有在从cronjob运行时它才会发生。

命令

/path/to/php/binary/php /path/to/php/file/IpcServer.php

分叉代码：

$iParent = posix_getpid();
$iChild  = pcntl_fork();

if ($iChild == -1)
    throw new Exception("Unable to fork into child process.");

elseif ($iChild)
{
    echo "Forking into background [{$iChild}].\n";

    Log::d('Killing parent process (' . $iParent. ').');
    exit;
}

输出

Forking into background [20835].
Killing parent process (20834).

ps aux | grep php

root 20834 0.0 0.0 0 0 ? Zs 14:28 0:00 [php] <defunct>
root 20835 0.0 0.2 275620 8064 ? Ss 15:35 0:00 /path/to/php/binary/php /path/to/php/file/IpcServer.php

我发现这是一个已知的apache错误，但是为什么我从cronjob运行时会遇到这个错误？

Answer 1

在PHP中，除非父母等待pcntl_wait()或pcntl_waitpid()返回，否则孩子将成为僵尸进程。一旦所有进程结束或处理，僵尸将被销毁。如果没有处理孩子并且孩子的跑步时间比父母长，那么看起来父母也会变成僵尸。

来自pcntl_fork页面的示例：

$pid = pcntl_fork();
if ($pid == -1) {
     die('could not fork');
} else if ($pid) {
     // we are the parent
     pcntl_wait($status); //Protect against Zombie children
} else {
     // we are the child
}

或者像这样使用信号处理来防止在主线程上等待：

$processes = array(); // List of running processes
$signal_queue = array(); // List of signals for main thread read
// register signal handler
pcntl_signal(SIGCHLD, 'childSignalHandler');

// fork. Can loop around this for lots of children too.
switch ($pid = pcntl_fork()) {
    case -1: // FAILED
        break;
    case 0: // CHILD
        break;
    default: // PARENT
        // ID the process. Auto Increment or whatever unique thing you want
        $processes[$pid] = $someID;
        if(isset($signal_queue[$pid])){
            childSignalHandler(SIGCHLD, $pid, $signal_queue[$pid]);
            unset($signal_queue[$pid]);
        }
        break;
}

function childSignalHandler($signo, $pid=null, $status=null){
    global $processes, $signal_queue;
    // If no pid is provided, Let's wait to figure out which child process ended
    if(!$pid){
        $pid = pcntl_waitpid(-1, $status, WNOHANG);
    }

    // Get all exited children
    while($pid > 0){
        if($pid && isset($processes[$pid])){
            // I don't care about exit status right now.
            //  $exitCode = pcntl_wexitstatus($status);
            //  if($exitCode != 0){
            //      echo "$pid exited with status ".$exitCode."\n";
            //  }
            // Process is finished, so remove it from the list.
            unset($processes[$pid]);
        }
        else if($pid){
            // Job finished before the parent process could record it as launched.
            // Store it to handle when the parent process is ready
            $signal_queue[$pid] = $status;
        }
        $pid = pcntl_waitpid(-1, $status, WNOHANG);
    }
    return true;
}

pcntl_fork（）导致已失效的父进程

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