International PHP Conference Berlin 2025

    pcntl_wait

    (PHP 5, PHP 7, PHP 8)

    pcntl_wait — 等待或返回 fork 的子进程状态

    说明

    pcntl_wait(int &$status, int $flags = 0, array &$resource_usage = []): int

    wait 函数挂起当前进程的执行直到一个子进程退出或接收到一个信号要求中断当前进程或调用一个信号处理函数。如果一个子进程在调用此函数时已经退出（俗称僵尸进程），此函数立刻返回。子进程使用的所有系统资源将被释放。关于 wait 在您系统上工作的详细规范请查看您系统的 wait（2）手册。

    注意:

    这个函数等同于以 -1 作为参数 process_id 的值并且没有 flags 参数来调用 pcntl_waitpid() 函数。

    参数

    status

    pcntl_wait() 将会存储状态信息到 status 参数上，这个通过 status 参数返回的状态信息可以用以下函数 pcntl_wifexited()、 pcntl_wifstopped()、 pcntl_wifsignaled()、 pcntl_wexitstatus()、 pcntl_wtermsig() 以及 pcntl_wstopsig() 获取其具体的值。

    flags

    如果操作系统（多数 BSD 类系统）允许使用 wait3，可以提供可选的 flags 参数。如果这个参数没有提供，wait 将会被用作系统调用。如果 wait3 不可用，提供参数 flags 不会有任何效果。flags 的值可以是以下两个常量中 0 个或多个 OR 运算的结果：

    flags 可用值
    WNOHANG 如果没有子进程退出立刻返回。
    WUNTRACED 子进程已经退出并且其状态未报告时返回。

    返回值

    pcntl_wait() 返回退出的子进程进程号，发生错误时返回 -1，如果提供了 WNOHANG 作为 option（wait3 可用的系统）并且没有可用子进程时返回 0。

    参见

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    用户贡献的备注 7 notes

    up
    6
    federico at nextware dot it
    18 years ago
    This a simple multi process application where you can choose
    the maximun process that can run at the same time.
    This is useful when you need to limit the fork of process.
    When the MAXPROCESS is reached the program wait on pcntl_wait()

    <?php

    DEFINE    (MAXPROCESS,25);

    for (    $i=0;$i<100;$i++){
    $pid = pcntl_fork();

    if (    $pid == -1) {
    die(    "could not fork");
    } elseif (    $pid) {
    echo     "I'm the Parent $i\n";
    $execute++;
    if (    $execute>=MAXPROCESS){
    pcntl_wait($status);
    $execute--;
    }
    } else {
    echo     "I am the child, $i pid = $pid \n";
    sleep(rand(1,3));
    echo     "Bye Bye from $i\n";
    exit;
    }
    }
    ?>
    up
    3
    duerra at yahoo dot com
    14 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.

    <?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);
    $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;
    }
    }
    up
    2
    gaylord at 100days dot de
    14 years ago
    pcntl_wait will not terminate on signals if you have a PHP signal handler activated (pcntl_signal).
    This is unless the signal handler was activated with 3rd parameter=true.

    Example:
    <?php
    declare(ticks=1);
    pcntl_signal(SIGTERM, "myHandler");
    $pid=pcntl_wait($status);
    ?>

    This will not terminate on SIGTERM sent to the process, because "wait" will be restarted after php recieves the signal. The signal handler "myHandler" will not be called unless pcntl_wait terminates for some other reason.

    Change to:
    <?php
    declare(ticks=1);
    pcntl_signal(SIGTERM, "myHandler", true);
    $pid=pcntl_wait($status);
    ?>

    Now the pcntl_wait terminates when a signal comes in and "myHandler" will be called on SIGTERM. (Make sure to put the wait in a loop though, because it will now not only terminate when a child exits but also when a signal arrives. Test for $pid>0 to detect a exit message from a child)
    (thanks to Andrey for helping me debugging this)
    up
    0
    duerra at yahoo dot com
    14 years ago
    Oops, I stripped just a little much from the job daemon code in the previous comment. You'll want to add a little line before the ->launchJob() method is called:

    <?php

    while(count($this->currentJobs) >= $this->maxProcesses){
    echo     "Maximum children allowed, waiting...\n";
    sleep(1);
    }
    up
    0
    digitalaudiorock at gmail dot com
    14 years ago
    I was unable to get pcntl_wait or pcntl_waitpid to terminate when I had an active signal handler. I then noticed the post below from gaylord at 100days dot de, however I'm a little confused by that post as I found the exact opposite to be true. The default value of the third parameter of pcntl_signal (the restart_syscalls parameter) is true and this seems to cause the wait to continue when the signal arrives. In order to prevent this I had to expressly set it to false. That is:

    pcntl_signal(SIGTERM, 'my_handler_function', false);
    up
    0
    thisisroot at gmail dot com
    19 years ago
    Below is a simple example of forking some children and timing the total duration (useful for stress tests).

    <?php

    $isParent     = true;
    $children = array();
    $start = microtime( true);

    /* Fork you!
    * (Sorry, I had to)
    */
    $ceiling = $CONCURRENCY - 1;

    for (     $i = 0; (( $i < $ceiling) && ( $isParent)); $i++) {
    $pid = pcntl_fork();
    if (     $pid === 0) {
    $isParent = false;

    } elseif (     $pid != -1) {
    $children[] = $pid;

    }

    }

    /* Process body */
    echo "Do stuff here\n";

    /* Cleanup */
    if ( $isParent) {
    $status = null;
    while (     count( $children)) {
    pcntl_wait( $status);
    array_pop( $children);
    }

    echo     "Completed in " . ( microtime( true) - $start) . " seconds.\n";

    }

    ?>
    up
    -1
    thomas dot nicolai at unisg dot ch
    18 years ago
    The code before isnt working for me cause the children are correctly started but not refreshed after they died. So keep in mind to use this instead and use the signal handler to know when a child exits to know when you have to start a new one. I added a few lines to the posting from {andy at cbeyond dot net} cause his post wasnt working for me as well (PHP5.1). Same effect like the one below.

    <?php
    declare(ticks = 1);

    $max=5;
    $child=0;

    // function for signal handler
    function sig_handler($signo) {
    global     $child;
    switch (    $signo) {
    case     SIGCHLD:
    echo     "SIGCHLD received\n";
    $child--;
    }
    }

    // install signal handler for dead kids
    pcntl_signal(SIGCHLD, "sig_handler");

    while (    1){
    $child++;
    $pid=pcntl_fork();

    if (    $pid == -1) {
    die(    "could not fork");
    } else if (    $pid) {

    // we are the parent
    if ( $child >= $max ){
    pcntl_wait($status);
    $child++;
    }
    } else {
    // we are the child
    echo "\t Starting new child | now we de have $child child processes\n";
    // presumably doing something interesting
    sleep(rand(3,5));
    exit;
    }
    }
    ?>
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