[Process] Process doesn't start if calling script terminates to quickly

[jeffreymb]

I am attempting to use the Process component to spaw a second (long running) process. I use ProcessBuilder to create the process, then call $process->start(). The process will only actually execute if I make my calling script sleep(1). If it terminates immediately, the new process will not execute.

Is there a way to solve this?

[pborreli]

You should check this article

Instead of using run() to execute a process, you can start() it: run() is blocking and waits for the process to finish, start() creates a background process. One way to get feedback from a running command is to pass a callback when starting/running the process

Did you try to setup a callback ? like it's shown in the example ?

[jeffreymb]

@pborreli I've read that article as well as most of the code for the Process class. As I said in my issue above, I am using the start() method, not run().

[pborreli]

@iCode4food are you trying to launch a zombie process ? (and you didn't answered my question, are you using a callback to get feedback)

[jeffreymb]

I'm developing and deploying on Windows. To add a few more details... I have a long running process that the user will initiate from the website. Instead of having the request wait for several minutes, I want a second process to actually do the work, and the client will ping the server to see if it is done and get status updates. The second, long running process that I'm executing is a Symfony CLI command.

[pborreli]

using a sleep is not bad then, I would do :

$p->start();
while ($p->isRunning()) {
    // running
    usleep(10000);
}
// done

[jeffreymb]

@pborreli That is exactly what I'm wanting to avoid. I don't want the clien'ts request to wait until the command is done executing, I want it to terminate, send it's output to the client and then ping the server until the long running command is done.

[pborreli]

have you seen #5759 and #5476 ? I guess getting the PID of the process could help you to retrieve it afterwards, PR are closed in favor of a not-yet existent ProcessChain (afaik)

[jeffreymb]

Apparently I'm not communicating my issue clearly. All that I need to do is allow the child process to continue executing after the parent request is completed. It seems that the parent request ends before the new child process is actually started and thus never starts. If I add sleep(1) after start(), all is well and fine, the child process will spin up and go to work, but I don't like the idea of having to sleep(1) just to wait for the new process to get rolling before the parent request can complete.

[romainneutron]

I think I understand what you're doing @iCode4food ; You're trying to send an HTTP response and run a process while the response has been sent. Actually, this is not recommended to run a process through an URI, it will lead you to some security flaw. It is recommended to use a message queue such as RabbitMQ and some workers to get the job done.

If you realy want to implement your design, you have to be sure that you're working with PHP fpm wich provides fastcgi_finish_request (see http://php.net/manual/en/install.fpm.php) AND run your process on KernelEvents::TERMINATE. Implementing this should work out of the box without any need for sleep or anything

[ewebcorporation]

I have the same problem with Process component.
i use the process component to do some tasks for database management, and i've made some symfony command.

The only way i found to do in real background is with nohup (but only on linux):

   $processtorun = new Process('nohup php ../app/console sw:execute &');
    $processtorun->start();

using symfony command can prevent a little bit for error, but not for infinite loop, and be sure you doesn't have max_execution_time in php.ini (nomally disabled by default for cli).
Put manually max_execution_time in your script.
this solution is not as good as @romainneutron wrote, but it's work

[kentpachi]

thank you very much

i managed it to get it works but there's nothing to do with "no hup" in my case.

the "../app/console" triggered the process while "app/console" did not.

so thanks !

[miniyarov]

@iCode4food I guess you might still be interested for the answer as the problem continues to exist in Process component. I resolved the issue by making a little change in Process class. change updateStatus(false) to updateStatus(true) in start method (https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/Process/Process.php#L301). stream_select will wait for the process to start, thus launching your command.

[romainneutron]

Hello @miniyarov ,

The solution you provide is wrong: If you do this change and run the test suite, you'll see that tests would fail. Process::start should be non-blocking.

It seems you expect a blocking Process (a process that does not stop if PHP stops). In this case, you have to use Process:run or a polling loop like:

$process->start();
while ($process->isRunning()) {
    // do things here
    usleep(50000);
}

[jpilldev]

Hi.

Did you solve this problem?

I have now the same behavior, i can run a command with run method, but with start method i got an error:

*dots in command are not in real command is just to avoid all parameters here

local.ERROR: The command "ffmpeg -re -i "video1.mp4"  -acodec libmp3lame..." failed.

Exit Code: ()

Working directory: /root

Output:
================


Error Output:
================
 {"exception":"[object] (Symfony\\Component\\Process\\Exception\\ProcessFailedException(code: 0): The command \"ffmpeg -re -i "video1.mp4"  -acodec libmp3lame..." failed.

Exit Code: ()

With run function the command executes fine, so, i don't know what to do.

I need the process to run asynchronously because it could be many of them and each can take around 5 mins.

[stof]

@jpilldev PHP will kill the subprocess when the main process dies. So even if you start the subprocess asynchronously to be able to keep using the main process while it runs, you should still ensure that your main process does not die before its child process.

[ttk]

When using Symfony's Process class in a cli environment, it is possible to keep the process running even after the main script ends. To do this, implement your own class and overload the __destruct() method to prevent the default behaviour that stops the process by sending a SIGTERM signal.

class PersistentProcess extends Process {
  public function __destruct() {}
}

IMO, I think the Process class should allow the option to not send SIGTERM when the Process object is destroyed.

[gsouf]

@ttk very good point.

I think the behavior of symfony/process 2 was to keep things running. As of symfony 3 it's closing when script terminates

[max4ever]

When using Symfony's Process class in a cli environment, it is possible to keep the process running even after the main script ends. To do this, implement your own class and overload the __destruct() method to prevent the default behaviour that stops the process by sending a SIGTERM signal.

class PersistentProcess extends Process {
  public function __destruct() {}
}

IMO, I think the Process class should allow the option to not send SIGTERM when the Process object is destroyed.

Also adding sleep(1) helped for some reason

        $process = new PersistentProcess($cmd);
        $process->start();

        sleep(1);//give it some time to start