Asynchronous HTTP requests in PHP

Question

Is there any sane way to make a HTTP request asynchronously in PHP without throwing out the response? I.e., something similar to AJAX - the PHP script initiates the request, does it's own thing and later, when the response is received, a callback function/method or another script handles the response.

One approach has crossed my mind - spawning a new php process with another script for each request - the second script does the request, waits for the response and then parses the data and does whatever it should, while the original script goes on spawning new processes. I have doubts, though, about performance in this case - there must be some performance penalty from having to create a new process every time.

Answer 1

Yes, depending on the traffic of your site, spawning a separate PHP process for running a script could be devastating. It would be more efficient to use shell_exec() to start a background process that saves the output to a filename you already know, but even this could be resource intensive.

You could also have a request queue stored in a database. A single, separate background process would pull the job, execute it, and save the output, possibly setting a flag in the DB that your web process could check.

If you're going to use the DB queue approach, use curl_multi* class of functions to send all queued requests at once. This will limit the execution time of each iteration in your background process to the longest request time.

Answer 2

V5 may not be threaded, but you can create applications that exploit in-process multitasking.

Check out the following article: "Develop multitasking applications with PHP V5" from IBM DeveloperWorks. You can find it here http://www.ibm.com/developerworks/web/library/os-php-multitask/