Force freeing memory in PHP

Question

In a PHP program, I sequentially read a bunch of files (with file_get_contents), gzdecode them, json_decode the result, analyze the contents, throw most of it away, and store about 1% in an array.

Unfortunately, with each iteration (I traverse over an array containing the filenames), there seems to be some memory lost (according to memory_get_peak_usage, about 2-10 MB each time). I have double- and triple-checked my code; I am not storing unneeded data in the loop (and the needed data hardly exceeds about 10MB overall), but I am frequently rewriting (actually, strings in an array). Apparently, PHP does not free the memory correctly, thus using more and more RAM until it hits the limit.

Is there any way to do a forced garbage collection? Or, at least, to find out where the memory is used?

Answer 1

Call memory_get_peak_usage() after each statement, and ensure you unset() everything you can. If you are iterating with foreach(), use a referenced variable to avoid making a copy of the original (foreach()).

foreach( $x as &$y)

If PHP is actually leaking memory a forced garbage collection won't make any difference.

There's a good article on PHP memory leaks and their detection at IBM

Answer 2

In PHP >= 5.3.0, you can call gc_collect_cycles() to force a GC pass.

Note: You need to have zend.enable_gc enabled in your php.ini enabled, or call gc_enable() to activate the circular reference collector.