Функции модуля PCNTL

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Дополнительную информацию содержит раздел «Функции модуля POSIX».

Содержание

pcntl_alarm — Устанавливает таймер доставки сигнала SIGALRM
pcntl_async_signals — Включить/отключить асинхронную обработку сигналов, либо получить текущий статус
pcntl_errno — Псевдоним pcntl_get_last_error
pcntl_exec — Выполняет указанную программу в пространстве текущего процесса
pcntl_fork — Разветвить (fork) текущий запущенный процесс
pcntl_get_last_error — Извлекает номер ошибки, который установила последняя функция модуля pcntl, которая завершилась ошибкой
pcntl_getpriority — Получить значение приоритета процесса
pcntl_rfork — Взаимодействует с ресурсами процесса
pcntl_setpriority — Изменить приоритет процесса
pcntl_signal — Установка обработчика сигнала
pcntl_signal_dispatch — Вызывает обработчики для ожидающих сигналов
pcntl_signal_get_handler — Получить текущий обработчик указанного сигнала
pcntl_sigprocmask — Задаёт и извлекает список блокируемых сигналов
pcntl_sigtimedwait — Ожидает сигналы в течение заданного времени
pcntl_sigwaitinfo — Ожидание сигналов
pcntl_strerror — Извлекает сообщение о системной ошибке, которое связано с номером ошибки
pcntl_unshare — Разделяет части контекста выполнения процесса
pcntl_wait — Ожидает или возвращает статус порождённого дочернего процесса
pcntl_waitid — Ожидает, пока дочерний процесс изменит состояние
pcntl_waitpid — Ожидает или возвращает статус порождённого дочернего процесса
pcntl_wexitstatus — Получить код возврата завершённого дочернего процесса
pcntl_wifexited — Проверяет, соответствует ли код завершения процесса нормальному завершению
pcntl_wifsignaled — Проверить, соответствует ли код завершения процесса завершению по сигналу
pcntl_wifstopped — Проверяет, остановлен ли дочерний процесс
pcntl_wstopsig — Получить сигнал, из-за которого был остановлен дочерний процесс
pcntl_wtermsig — Получить сигнал, из-за которого был принудительно завершён дочерний процесс

Улучшение страницы

Инструкция • Исправление • Сообщение об ошибке

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Примечания пользователей 18 notes

down

kevin at vanzonneveld dot net ¶

16 years ago

If you want to create a daemon in PHP, consider using System_Daemon http://pear.php.net/package/System_Daemon

Install it like this:
pear install -f system_daemon

Then use it like this:
<?php
// Include PEAR's Daemon Class
require_once "System/Daemon.php";

// Bare minimum setup
System_Daemon::setOption("appName", "mydaemonname");

// Spawn Deamon!
System_Daemon::start();

// Your PHP Here!
while (true) {
    doTask();
}

// Stop daemon!
System_Daemon::stop();
?>

More examples can be found inside the PEAR package.

down

registrazioni at XSPAMX dot tassetti dot net ¶

17 years ago

(PHP 5.2.4) 

This is an example of multithreading keeping different connections to a mysql database: when children exit they close the connection and others can't use it any more generating problems. In this example I used variable variables to make a different connection per each child. 

This scripts loops forever with one mother detached from the terminal and five children 'named' from 1 to 5. When one children sees it's name in the database (one table 'test.tb' with only one field 'test') he lets himself die. To kill children insert their value in the db. The mother suicides only when all children are dead.

What a sad but interesting story...

    $npid = pcntl_fork(); // DETACH FROM TERMINAL AND BE REAPED BY INIT

    if ($npid==-1) die("Error: impossible to pcntl_fork()\n");
    else if ($npid) exit(0); // THE GRANPA DIES
    else // MOTHER GOES ON TO MAKE CHILDREN
    {
        $children = 5;
        for ($i=1; $i<=$children; $i++)
        {
            $pid = pcntl_fork();
            if ($pid==-1) die("Error: impossible to pcntl_fork()\n");
            else if ($pid)
            {
                 $pid_arr[$i] = $pid;
            }
            if (!$pid) // CHILDREN
            {
                global $vconn;
                $vconn = "vconn$i";
                global $$vconn;
                $$vconn = @mysql_connect("mydbhost","mydbuser","mydbpwd");
                if (!($$vconn)) echo mysql_error();
                if (!($$vconn)) exit;

                while (1)
                {
                    $query = "SELECT test FROM test.tb";
                    $rs = mysql_query($query,$$vconn);
                    $rw = mysql_fetch_row($rs);
                    if ($rw[0]==$i) exit;
                    else
                    {
                        echo "Database is $rw[0] and I am $i, it's not my time, I will wait....\n";
                        sleep(1);
                    }
                }
            }
        }

        foreach ($pid_arr as $pid)
        {
            // we are the parent and we wait for all children to die
            pcntl_waitpid($pid, $status);
        }
        echo "All my children died, I will suicide...\n";
        exit();
    }

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kementeusNOSPAM at gmail dot com ¶

17 years ago

In the example of the documentation we need to put the pctnl_signal statements BEFORE the while loop.

In that way we can execute whatever we put in the signal handler functions.

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David Koopman ¶

21 years ago

I had a hard time finding a complete example of using PHP as a multi-process (or multi-threaded - I don't understand the difference in these two terms) daemon using connection pooling.  I put pieces of the puzzle together and came up with the program below.  I hope it helps someone.  Notes about making this work:

1) I rebuilt PHP on my machine with these config options:
./configure --enable-sockets --enable-pcntl --enable-sigchild
make
make install

2) I have problems when tried to handle SIGTERM and SIGHUP myself, so I removed these from my code, don't use them unless you have a special need for this:
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");

What I do is: 
1. start the program, then fork to detach from the terminal (kill the parent and make the child the session leader).

2. bind to address and port and start listening.

3. fork $poolNum times, creating $poolNum children (this is the pool of daemons running.  The children handle the incoming connections).

4. keep the parent process running in a loop, constantly checking to see if it should create a new child.  It will always keep $poolNum spare children ready (as long as the total pooled connections doesn't exceed $maxDaemon).  As connections come in, more children are spawned. 

5. When a new connection comes in, it is handed off to the first child.  This child then sends a SIGUSR1 signal back to the parent.  The parent has a signal handler for SIGUSR1, which will increment the $numActive variable by one.  The loop that is running (see 4 above) will note the increment in $numActive and automatically create a new child process to keep the process pool going.

I have to post the code in the next note, the note engine on this site won't allow such a long note to be posted, but I think this code example is well worth a comment on this...

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luca dot mariano at email dot it ¶

21 years ago

Hi folks,
if someone uses PHP-CLI onWin32 and wants to experiment the PCNTL stuff, I've packed a binary version of PHP with built-in pcntl, shmop, sysvshm and other typical Unix extensions... (thanks to Cygwin DLLs).
Download it: http://phplet.sf.net/modules.php?name=Web_Links&l_op=visit&lid=4

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debasiss at mindfiresolutions dot com ¶

5 years ago

<?php
/**
 * @file
 * Working demo of simulating parallel process in PHP.
 */

// ****                       **** //
print "Main program started.... \n";
// Start two child processes.
createProcess("Job1");
createProcess("Job2");
print " *** Child Process started *** \n";

while (TRUE) {

 $pid = pcntl_waitpid(0, $status, WNOHANG);
    if ($pid > 0) {
        childProcessComplete($pid);
    }else if($pid === -1){
        print " *** Child Process Completed *** \n";
        allChildProcessComplete();
        exit();
    }

}
print "Main program end. \n";

/**
 * Method to start child process.
 */
function startChildProcess($childProcessName) {
    $executionTime = rand(5, 10);

    if($childProcessName === "Job1"){
        print "Starting Job1 on processId " .getmypid()."  at " . date('l jS \of F Y h:i:s A') . " expected time $executionTime seconds\n";
    }else if($childProcessName === "Job2"){
        print "Starting Job2 on processId " .getmypid()."  at " . date('l jS \of F Y h:i:s A') . " expected time $executionTime seconds\n";
    }

    // Simulate doing actual work with sleep().
    sleep($executionTime);
}

/**
 * Method to notify when system unable to start a process.
 */
function errorOnProcessLunch() {
    print "Failed to lunch process \n";
}

/**
 * Method to notify when a child process complete the task.
 */
function childProcessComplete($pid) {
    print "Child processing is done for $pid  at " . date('l jS \of F Y h:i:s A') . " \n";
}

/**
 * Method to create a new process.
 */
function createProcess($pname) {
    $pid = pcntl_fork();

    if ($pid == -1) {
        errorOnProcessLunch();
    }
    else if ($pid === 0) {
        startChildProcess($pname);
        exit(); // Make sure to exit.
    }
    else {
        startParentProcess($pid);
    }

}

/**
 * Method to notify when parent thread execute.
 */
function startParentProcess($childProcessID){
    print "In parent thread created child processid $childProcessID \n";
}

/**
 * Method to notify when all child process has completed the task.
 */
function allChildProcessComplete(){
    print "All child processing completed \n";
}

?>

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jeremy at nirvani dot net ¶

21 years ago

#!/usr/local/bin/php -q
<?php

# Jeremy Brand <jeremy@nirvani.net>
# http://www.nirvani.net/

# ./configure --enable-pcntl --enable-sigchild
# make
# make install

# This code example shows how to use a script to do multiprocessing.  Each time
# this script is ran, the result is 5 (in this example) processes running to
# accomplish a specified task.

# Examples could be a messaging queue.  You could get the number of messages in
# a queue and handle any or all of them asynchronously.

# Get the number of children you want to be born by running this
# script once.
$children = 5; # likely a function call here.

for ($i=1; $i<=$children; $i++)
{

  $pid = pcntl_fork();
  if ($pid == -1)
  {
    die("could not fork\n");
  }
  else if ($pid)
  {
    # If we are the parent, we did our job of giving birth,
    # now lets finish our job and die!
    exit(0);
  }
  else
  {
    # Since we are the child, fork so that init will become our parent.  Init
    # is good at wait()ing on children - ie: reaping.
    $cpid = pcntl_fork();
    if ($cpid == -1)
    {
      die("could not fork in child process\n");
    }
    if (!$cpid)
    {
      # We have now forked off from our parent and also are not waiting on any
      # other children to process, however other children are running
      # simutaniously to us.  Make sure the code you write here is safe to run
      # in this environment of multiprocessing - ie: proper locking, etc.
      # Write the custom code here that you want to multiprocess.

      # ADD CODE HERE TO MULTIPROCESS
      print "we are child number $i\n";

      # Don't forget to exit after the child processing is done.  Certainly
      # change this exit code if you need to however.
      exit(0);
    }
  }
}

?>

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keksov[at]gmx.de ¶

22 years ago

You have to use socket_select before socket_accept, so your code will wait for connection with select. socket_select can be interrupted by signals easily. Below is an example from my library (methods of class TNetSocket):
  //-- select
  function select($aread=NULL,$awrite=NULL,$aexcept=NULL,$timeout=NULL)
  {
    while(1)
    {
      $res="";
      $res=socket_select($aread, $awrite, $aexcept, $timeout);

      // if errno===0 it means what select was interrrupted by SysV signal
      if($res===false && socket_last_error($this->socket())!==0)
      { // error occured, interrupted not by a signal
        $this->set_socket_error(__LINE__);
        return(false);
      }
      break;
    }
    return(true);
  }

  //-- accept, wait for incomming connection
  function accept()
  {
    $this->clear_socket_error();
    $this->set_io_socket(_SOCKET_);

    $socket=$this->socket();
    $aread=array($socket);
    if ($this->select($a=&$aread)===false)
      return(false);

    $child_socket=socket_accept($this->socket);
    if($child_socket <= 0)
    { // error occured
      $this->set_socket_error(__LINE__);
      return(false);
    }

    $this->child_socket=$child_socket;
    $this->sockets[_CHILD_SOCKET_]=&$this->child_socket;
    $this->set_io_socket(_CHILD_SOCKET_);

    $a=&$this->peername;
    $res=socket_getpeername($child_socket,$a);

    if($res <= 0)
    { // error occured
      $this->set_socket_error(__LINE__);
      return(false);
    }

    $this->get_address_and_port(_CHILD_SOCKET_);
    TLogManager::phpserv("Connection accepted. ADDRESS $this->address, PORT $this->port","net_socket",__FILE__,__LINE__);

    $this->connected=true;
    return(true); // return new object of TNetSocket type
  }

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Anonymous ¶

20 years ago

in example 1, i found unless i create function sig_handler _BEFORE_ pcnt_signal, it wouldnt work.. and would just fall to the floor bleeding to death

(note for people having these kinda probs)

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cameronNO_SPAM at tripdubdev dot com ¶

21 years ago

I'm currently working on some code for this, but in case I forget to come back to post to the board, or in case it takes me a while, why not just have a separate background job running (started up via the shell) that tracks which sockets are available to clients ?  Then all you'd have to do is communicate with the one job (or perhaps its own mini-server) run in the background that keeps an array of the available sockets for the server.  This seems the most natural alternative since PHP disclaims that process control functionality should not be used in a web-server environment.  I would hate to build a server, especially one with high traffic, that had to run through a loop in order to find an available socket.

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schst at php dot net ¶

21 years ago

To get rid of the zombies when child processes terminate you do not have to write a lot of code that uses complex stuff like message queues.
Instead you only set a signal handler:

pcntl_signal(SIGCHLD, SIG_IGN);

Stephan

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daniel[at]lorch.cc ¶

22 years ago

This piece of code helped me to find out what signals are being sent to my process:

function sig_identify($signo) {
  switch($signo) {
    case SIGFPE:    return 'SIGFPE';
    case SIGSTOP:   return 'SIGSTOP';
    case SIGHUP:    return 'SIGHUP';
    case SIGINT:    return 'SIGINT';
    case SIGQUIT:   return 'SIGQUIT';
    case SIGILL:    return 'SIGILL';
    case SIGTRAP:   return 'SIGTRAP';
    case SIGABRT:   return 'SIGABRT';
    case SIGIOT:    return 'SIGIOT';
    case SIGBUS:    return 'SIGBUS';
    case SIGPOLL:   return 'SIGPOLL';
    case SIGSYS:    return 'SIGSYS';
    case SIGCONT:   return 'SIGCONT';
    case SIGUSR1:   return 'SIGUSR1';
    case SIGUSR2:   return 'SIGUSR2';
    case SIGSEGV:   return 'SIGSEGV';
    case SIGPIPE:   return 'SIGPIPE';
    case SIGALRM:   return 'SIGALRM';
    case SIGTERM:   return 'SIGTERM';
    case SIGSTKFLT: return 'SIGSTKFLT';
    case SIGCHLD:   return 'SIGCHLD';
    case SIGCLD:    return 'SIGCLD';
    case SIGIO:     return 'SIGIO';
    case SIGKILL:   return 'SIGKILL';
    case SIGTSTP:   return 'SIGTSTP';
    case SIGTTIN:   return 'SIGTTIN';
    case SIGTTOU:   return 'SIGTTOU';
    case SIGURG:    return 'SIGURG';
    case SIGXCPU:   return 'SIGXCPU';
    case SIGXFSZ:   return 'SIGXFSZ';
    case SIGVTALRM: return 'SIGVTALRM';
    case SIGPROF:   return 'SIGPROF';
    case SIGWINCH:  return 'SIGWINCH';
    case SIGPWR:    return 'SIGPWR';
  }
}

function sig_handler($signo) {
  echo "Caught " . sig_identify($signo) . " (" . $signo  . ") on " . posix_getpid() . "\n";
}

pcntl_signal(SIGFPE, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");
// pcntl_signal(SIGINT, "sig_handler");
pcntl_signal(SIGQUIT, "sig_handler");
pcntl_signal(SIGILL, "sig_handler");
pcntl_signal(SIGTRAP, "sig_handler");
pcntl_signal(SIGABRT, "sig_handler");
pcntl_signal(SIGIOT, "sig_handler");
pcntl_signal(SIGBUS, "sig_handler");
pcntl_signal(SIGPOLL, "sig_handler");
pcntl_signal(SIGSYS, "sig_handler");
pcntl_signal(SIGCONT, "sig_handler");
pcntl_signal(SIGUSR1, "sig_handler");
pcntl_signal(SIGUSR2, "sig_handler");
pcntl_signal(SIGSEGV, "sig_handler");
pcntl_signal(SIGPIPE, "sig_handler");
pcntl_signal(SIGALRM, "sig_handler");
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGSTKFLT, "sig_handler");
pcntl_signal(SIGCHLD, "sig_handler");
pcntl_signal(SIGCLD, "sig_handler");
pcntl_signal(SIGIO, "sig_handler");
pcntl_signal(SIGTSTP, "sig_handler");
pcntl_signal(SIGTTIN, "sig_handler");
pcntl_signal(SIGTTOU, "sig_handler");
pcntl_signal(SIGURG, "sig_handler");
pcntl_signal(SIGXCPU, "sig_handler");
pcntl_signal(SIGXFSZ, "sig_handler");
pcntl_signal(SIGVTALRM, "sig_handler");
pcntl_signal(SIGPROF, "sig_handler");
pcntl_signal(SIGWINCH, "sig_handler");
pcntl_signal(SIGPWR, "sig_handler");

I commented out SIGNIT, as it is the signal which is sent to your process when you press CTRL-C. If you catch this signal, you must handle it properly:

function sig_handler($signo) {
  switch($signo) {
    case SIGINT:
      // customized cleanup code
      exit; // now exit
      break;
  }
}

Otherwise the only possibility to stop your process is by sending a SIGKILL signal - you can do this on the shell by typing "kill -9 PID" (where -9 is the numerical value for SIGKILL).

Note: You cannot add a handler (i.e. ignore signals) for SIGSTOP and SIGKILL - for obvious reasons.

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m dot quinton at gmail dot com ¶

16 years ago

a nice example of a class framework to manage tasks using pcntl_fork.

<?php

/**
 * author : Marc Quinton / April 2008.
 *
 *  a simple task management framework using pcntl_fork, pcntl_wait.
 *
 *  - see at bottom for a sample usage.
 *  - you shoud overring Task class (SleepingClass is an example), and manage them in a pool, using taskManager
 */

error_reporting(E_ALL);

class Task {

    protected $pid;
    protected $ppid;

    function __construct(){
    }

    function fork(){
        $pid = pcntl_fork();
        if ($pid == -1)
            throw new Exception ('fork error on Task object');
        elseif ($pid) {
            # we are in parent class
            $this->pid = $pid;
            # echo "< in parent with pid {$his->pid}\n";
        } else{
            # we are is child
            $this->run();
        }
    }

    function run(){
        # echo "> in child {$this->pid}\n";
        # sleep(rand(1,3));
        $this->ppid = posix_getppid();
        $this->pid = posix_getpid();
    }

    # call when a task in finished (in parent)
    function finish(){
        echo "task finished {$this->pid}\n";
    }

    function pid(){
        return $this->pid;
    }
}

class SleepingTask extends Task{
    function run(){
        parent::run();
        echo "> in child {$this->pid}\n";

        # print_r($this);

        sleep(rand(1,5));
        echo "> child done {$this->pid}\n";
        exit(0);
    }
}

class TaskManager{

    protected $pool;

    function __construct(){
        $this->pool = array();
    }

    function add_task($task){
        $this->pool[] = $task;
    }

    function run(){

        foreach($this->pool as $task){
            $task->fork();
        }

        # print_r($this);
        # sleep(60);

        while(1){
            echo "waiting\n";
            $pid = pcntl_wait($extra);
            if($pid == -1)
                break;

            echo ": task done : $pid\n";
            $this->finish_task($pid);
        }

        echo "processes done ; exiting\n";
        exit(0);
    }

    function finish_task($pid){
        if($task = $this->pid_to_task($pid))
            $task->finish();
    }

    function pid_to_task($pid){
        foreach($this->pool as $task){
            if($task->pid() == $pid)
                return $task;
        }
        return false;
    }
}

$manager = new TaskManager();

for($i=0 ; $i<10 ; $i++)
    $manager->add_task(new SleepingTask());

$manager->run();

?>

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flyingguillotine1968 at yahoo dot com ¶

17 years ago

ok, heres what ya do to handle child process's ... :> 

you want to pfork your main program, and let it exit, 
allowing the new child to become the main program (parent process).

example psudo code : 
main program start;
     ....
     if pfork'd child ok
          then exit ;

    // now your new child process is in control... 
    // use a signal handler to make it exit (sigkill or sigterm probably)
    // when this new process pforks, store the new child PID's in an
    // array.   when your process  catch's the sigterm  signal
    // loop thru the array of its child PID's sending each child
    // sigkill , then call  pwait on them to wait for them to exit.
    // this will make sure any child process are cleaned up ok
    // THEN .. now here's the trick.... 
    // reset yer sigterm handler BACK to its original default handler, 
   // thennnnn   raise sigterm , main program will exit ok now tooooo :> 

  
example: 
when your pfork'd main process gets sigterm ... then do something 
like this : 

foreach ($this->pForkList as $kiddie) {
$deadPID    = 0;
$this->sendSignal(SIGKILL,$kiddie);
do {
$deadPID = pcntl_waitpid(-1,WNOHANG);
if ($deadPID > 0) {
// kiddie has exited now ... 
unset($this->pForkList[ array_search($deadPID,$this->pForkList)]);
break;
} // end if
} while ($deadPID == 0);

} // end for

// now reset sigterm ... 
$this->signalSet($sigNum,SIG_DFL);
// RAISE sigterm now ... 
$this->sendSignal(SIGTERM,$this->myPID);

this will allow your main process and all its child process's to exit properly and not leave and zombies or other bad stuff behind !

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van[at]webfreshener[dot]com ¶

22 years ago

Forking your PHP daemon will cause it to zombie on exit.



...or so I've seen on:

FreeBSD (PHP4.2.x)

Debian (PHP4.3.0-dev)

Darwin (PHP4.3.0-dev)



This was tested with the example code above and other scripts created for evaluation.



Seems adding --enable-sigchild to your configure will get rid of the problem.



Hope that saves some hair tearing :]

down

-2

andy at cbeyond dot net ¶

20 years ago

Suppose you want to fork off children to handle a few hundred different targets (like, say, SNMP polling, but that's just one example).  Since you don't want to fork-bomb yourself, here's one method of limiting the number of children you have in play at any one time:

#!/usr/bin/php -q
<?php
declare(ticks = 1);

$max=10;
$child=0;

// function for signal handler
function sig_handler($signo) {
  global $child;
  switch ($signo) {
    case SIGCHLD:
      echo "SIGCHLD received\n";
      $child -= 1;
  }
}

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

for ($i=1;$i<=20;$i++) {
        while ($child >= $max) {
                sleep(5); echo "\t Maximum children allowed\n";
                }
        $child++;
        $pid=pcntl_fork();
        if ($pid == -1) {
                die("could not fork");
        } else if ($pid) {
                // we are the parent
        } else {
                // we are the child
                echo "child number $i\n";
                // presumably doing something interesting
                sleep(15);
                exit;
        }
}

down

-1

corychristison at lavacube dot com ¶

20 years ago

An easier way than what was first suggested in the first comment, to retrieve what signal your application is being sent would be to use get_defined_constants() to list all constants, loop through and strip out those that are not signals, and to check if it matches the value.

Here is my code for doing this, written for PHP5 only.
<?php

// php5 Specfic

function pcntl_sig_identify ( $sig_no ) {
    $get_constants = get_defined_constants(true);
    $pcntl_contstants = $get_constants["pcntl"];
    $keys = array_keys( $pcntl_contstants );
      foreach($keys as $key){
        if(strstr($key, "SIG") && !strstr($key, "_") && $pcntl_contstants[$key] == $sig_no){
      return $key;
    }
      } // end loop
} // end function pcntl_sig_identify

// 
// This example will output "SIGTERM"
//

print pcntl_sig_identify(15) . "\n";

?>

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-1

Patrice Levesque ¶

21 years ago

So, you want to create multiple child processes and don't want any zombies, don't you?

You can use IPC to achieve just that.  Every child that is spawned has to tell its parent that time has come for him to be terminated.  So, yes, zombies will be created, but once in a while the parent will 'clean up' after his kids.  Code:

<?php
  declare(ticks = 1);
  // create a IPC message queue
  $msgqueue = msg_get_queue(ftok("/tmp/php_msgqueue.stat", 'R'),0666 | IPC_CREAT);
  // loop for 1000 children 
  for ($c = 0; $c < 1000; $c++) {
    // fork
    $pcid = pcntl_fork();
    if ($pcid == -1) {
      die("Could not fork!");
    }
    elseif ($pcid) { // we are the parent, look for zombie kids and terminate 'em
      // look in the IPC message queue if there are any entries
      $currentqueue = msg_stat_queue($msgqueue);
      $n = $currentqueue['msg_qnum']; // number of messages (number of kids to terminate)
      if ($n > 0) {
        echo "There are $n kids to terminate.\n";
        for ($i = 0; $i < $n; $i++) {
          // pop the kid's PID from the IPC message queue
          if (!msg_receive ($msgqueue, 1, $msg_type, 16384, $msg, true, 0, $msg_error)) {
            echo "MSG_RECV ERROR: $errmsg \n"; // something has gone wrong
          }
          else {
            pcntl_waitpid($msg, $tmpstat, 0); // terminate kid for real.
          };
        };
      };
    }
    else { // we are the child!
      if (!posix_setsid()) { die ("Could not detach"); }; // detach
      echo "I am child number $c\n";
      sleep(5); // do something useful
      // tell dad I'm finished via IPC: send him my PID
      if (!msg_send($msgqueue, 1, posix_getpid(), true, true, $errmsg)) {
        echo "MSG_SEND ERROR: $errmsg \n";
      };
      exit(); // become a zombie until dad kills me                            
    };
  };
?>

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