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    duerra at yahoo dot com
    15 years ago
    Using pcntl_fork() can be a little tricky in some situations. For fast jobs, a child can finish processing before the parent process has executed some code related to the launching of the process. The parent can receive a signal before it's ready to handle the child process' status. To handle this scenario, I add an id to a "queue" of processes in the signal handler that need to be cleaned up if the parent process is not yet ready to handle them.

    I am including a stripped down version of a job daemon that should get a person on the right track.

    <?php
    declare(ticks=1);
    //A very basic job daemon that you can extend to your needs.
    class JobDaemon{

    public     $maxProcesses = 25;
    protected     $jobsStarted = 0;
    protected     $currentJobs = array();
    protected     $signalQueue=array();
    protected     $parentPID;

    public function     __construct(){
    echo     "constructed \n";
    $this->parentPID = getmypid();
    pcntl_signal(SIGCHLD, array($this, "childSignalHandler"));
    }

    /**
    * Run the Daemon
    */
    public function run(){
    echo     "Running \n";
    for(    $i=0; $i<10000; $i++){
    $jobID = rand(0,10000000000000);

    while(    count($this->currentJobs) >= $this->maxProcesses){
    echo     "Maximum children allowed, waiting...\n";
    sleep(1);
    }

    $launched = $this->launchJob($jobID);
    }

    //Wait for child processes to finish before exiting here
    while(count($this->currentJobs)){
    echo     "Waiting for current jobs to finish... \n";
    sleep(1);
    }
    }

    /**
    * Launch a job from the job queue
    */
    protected function launchJob($jobID){
    $pid = pcntl_fork();
    if(    $pid == -1){
    //Problem launching the job
    error_log('Could not launch new job, exiting');
    return     false;
    }
    else if (    $pid){
    // Parent process
    // Sometimes you can receive a signal to the childSignalHandler function before this code executes if
    // the child script executes quickly enough!
    //
    $this->currentJobs[$pid] = $jobID;

    // In the event that a signal for this pid was caught before we get here, it will be in our signalQueue array
    // So let's go ahead and process it now as if we'd just received the signal
    if(isset($this->signalQueue[$pid])){
    echo     "found $pid in the signal queue, processing it now \n";
    $this->childSignalHandler(SIGCHLD, $pid, $this->signalQueue[$pid]);
    unset(    $this->signalQueue[$pid]);
    }
    }
    else{
    //Forked child, do your deeds....
    $exitStatus = 0; //Error code if you need to or whatever
    echo "Doing something fun in pid ".getmypid()."\n";
    exit(    $exitStatus);
    }
    return     true;
    }

    public function     childSignalHandler($signo, $pid=null, $status=null){

    //If no pid is provided, that means we're getting the signal from the system. Let's figure out
    //which child process ended
    if(!$pid){
    $pid = pcntl_waitpid(-1, $status, WNOHANG);
    }

    //Make sure we get all of the exited children
    while($pid > 0){
    if(    $pid && isset($this->currentJobs[$pid])){
    $exitCode = pcntl_wexitstatus($status);
    if(    $exitCode != 0){
    echo     "$pid exited with status ".$exitCode."\n";
    }
    unset(    $this->currentJobs[$pid]);
    }
    else if(    $pid){
    //Oh no, our job has finished before this parent process could even note that it had been launched!
    //Let's make note of it and handle it when the parent process is ready for it
    echo "..... Adding $pid to the signal queue ..... \n";
    $this->signalQueue[$pid] = $status;
    }
    $pid = pcntl_waitpid(-1, $status, WNOHANG);
    }
    return     true;
    }
    }

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