PHP garbage collection and memory leaks

25 Feb

tags: garbage collection, memory leak, php

Been working on a command line script that takes days to finish execution (yes, DAYS). Unfortunately, it had a healthy flow of memory leaking. It would fatally crash with your typical "out of memory" error.

I spent hours debugging the potential source - free'd results of mysql queries, unset variables, you name it I tried it. I kind of gave up and instead chose to add in a "start at" parameter so that I could just re-execute and jump back in to the loop where it crashed last time.

Today, through natural processes of improving functionality and cleaning code, I moved the block of code that was leaking memory into a function so that it could be recycled elsewhere. By simply moving the code into a function I suspect PHP now garbage collects after each call and memory no longer hemorrhages from its veins.

I hope this helps someone else out there!

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Paul

This helped... I'm working with objects, so it's a little different for me.

You need to cache objects that are created within a method, where the method's return value is the result of a function call on the newly created object.


class a {
  function b() { 
    $c = new c();
    // memory leaking here.
    return $c->d();
  }
}
class c { 
  function d() { 
    return 3+5;
  }
}

Fixed:
class a {
  var $objc;
  function b() { 
    // create if not exists, else use cached object.
    if( !is_object($this->objc) ) { 
      $this->objc = new c();
    }
    return $this->objc->d();
  }
}

Brandon Savage

This did help me. Thanks for posting it. I did exactly what you did and my application works properly.

Tom Lancaster

thanks for this insight. You've just saved me a lot of time on a script that I'm using to update my whole database. This technique works.

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