I am looking for the PHP equivalent for VB doevents

Question

I am looking for the PHP equivalent for VB doevents. I have written a realtime analysis package in VB and used doevents to release to the operating system. Doevents allows me to stay in memory and run continuously without filling up memory and allows me to respond to user input. I have rewritten the package in PHP and I am looking for that same doevents feature. If it doesn't exist I could reschedule myself and exit. But I currently don't know how to do that and I think that would add a lot more overhead. Thank you, gerardg

Answer 1

usleep is what you are looking for.. Delays program execution for the given number of micro seconds http://php.net/manual/en/function.usleep.php

Answer 2

It's been almost 10 years since I last wrote anything in VB and as I recall, doevents() function allowed the application to yield to the processor during intensive processing (usually to allow other system events to fire - the most common being WM_PAINT so that your UI won't appear hung).

I don't think PHP has such functionality - your script will run as a single process and end (either when it's done or when it hits the default 30 second timeout).

If you are thinking in terms of threads (as most Windows programmers tend to do) and needing to spawn more than 1 instance of your script, perhaps you should take look at PHP's Process Control functions as a start.

Answer 3

I'm not entirely sure which aspects of doevents you're looking to emulate, so here's pretty much everything that could be useful for you.

You can use ob_implicit_flush(true) at the top of your script to enable implicit output buffer flushing. That means that whenever your script calls echo or print or whatever you use to display stuff, PHP will automatically send it all to the user's browser. You could also just use ob_flush() after each call to display something, which acts more like Application.DoEvents() in VB with regards to keeping your UI active, but must be called each time something is output.

Naturally if your script uses the output buffer already, you could build a copy of the buffer before flushing, with ob_get_contents().

If you need to allow the script to run for more time than usual, you can set a longer tiemout with set_time_limit($time). If you need more memory, and you have access to edit your .htaccess file, place the following code and edit the value:

php_value memory_limit 64M

That sets the memory limit to 64 megabytes.

For running multiple scripts at once, you can use pcntl_exec to start another one running.

If I am missing something important about DoEvents(), let me know and I will try to help you make it work.

Answer 4

PHP is designed for asynchronous on demand processing. However it can be forced to become a background task with a little hackery.

As PHP is running as a single thread you do not have to worry about letting the CPU do other things as that is already taken care of. If this was not the case then a web server would only be able to serve up one page at a time and all other requests would have to sit in a queue. You will need to write some sort of look that never expires until some detectable condition happens (like the "now please exit" message you set in the DB or something).

As pointed out by others you will need to set_time_limit($something); with perhaps usleep stopping the code from running "too fast" if it eats very much CPU each loop. However if you are also using a Database connection most of your script time is actually the script waiting for the Database (by far the biggest overhead for a script).

I have seen PHP worker threads created by using screen and detatching it to a background task. Other approaches also work so long as you do not have a session that will time out or exit (say when the web browser is closed). A cron that starts a script to check if the script is running every x mins or hours gives you automatic recovery from forced exists and/or system restarts.

TL;DR: doevents is "baked in" to PHP and you don't have to worry about it.