Asynchronous PHP?

Question

I have a PHP script that does a lot of checks and then downloads a file to the server and outputs the original.
To download the file I use

system("/usr/local/bin/wget -O ...");

So php waits for the download to finish and then it outputs the file.
My question is if its possible to send a "ping" somewhere (other php file?) for the download to start and then without waiting for the result just continue with the execution.

does this help http://stackoverflow.com/questions/1296085/download-file-using-jquery ? — ka_lin, Jan 30 '12 at 10:08

score 2 · Answer 1 · answered Jan 30 '12 at 10:10

2

Use curl_multi_* functions to handle multiple-downloads in parallel. PHP lacks any kind of threading support and process forking is merely a hack.

answered Jan 30 '12 at 10:10

Sim

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I dont have multiple downloads, the file is only one. I just want to continue executing while the file is downloading. – Jim Jan 30 '12 at 13:44

score 1 · Answer 2 · answered Jan 30 '12 at 10:04

1

Use pcntl_fork() to fork your current process into a child process. Do the file download in the child process while your parent process can continue executing its task.

$pid = pcntl_fork(); 

if ( $pid == -1 ) 
{        
    // Fork failed            
    exit(1); 
} 
else if ( $pid ) 
{ 
    // The parent process
   //continue what you want to do here
} 
else 
{ 
    // the child process 
    // do the system call here
}

After doing some work, if you now need to parent process to wait until the child process finishes, you can pcntl_waitpid($pid).

Read here for more documentation on pcntl methods.

answered Jan 30 '12 at 10:04

Ayush

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pcntrl functions are not recommended for use in web environments and only work on *nix systems - http://uk.php.net/manual/en/intro.pcntl.php – Adam Hopkinson Jan 30 '12 at 10:07
Since he tagged the question linux, I think we can safely assume he's running it in a linux box. As for your other point, you are correct. Pcnlt functions only run from CLI. – Ayush Jan 30 '12 at 10:09
Still "not recommended for use in web environments" - as in, this will Crash And Burn at the worst possible moment. – Piskvor left the building Jan 30 '12 at 10:13
@Piskvor: It won't 'crash and burn'. If run from a cgi environment, it will gracefully throw an error since pcntl function does not exist in the CGI version of PHP – Ayush Jan 30 '12 at 10:27
@xbonez: Hmm, that would explain it - I've seen this on a web server, but it must have been hacked into the source by the locals, then. Explains the picturesque crashes. – Piskvor left the building Jan 30 '12 at 10:39

score 0 · Answer 3 · answered Jan 30 '12 at 11:33

A general design patters would be to apply a Command Design Pattern: http://en.wikipedia.org/wiki/Command_pattern

You can implement this in your local web environment or you could install some kind of queue server like: http://www.rabbitmq.com/ etc. etc.

It depends on your systems, access to them and your knowledge to see which solution would fit best That's a more complex question too far offtopic here.

In general the suggested pattern will allow you to fix your question without having lots of issues since it is a well-known and widely used approach to handle lots of tasks which take too long for doing directly within the request.

Asynchronous PHP?

3 Answers3

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