Re: When does PHP free-up memory allocated to it?

On Mon, May 21, 2007 4:23 am, Richard Davey wrote: > Quick question - does anyone know when PHP actually frees allocated > memory during the process of a script? When it can be sure that a variable is no longer needed. Specifically, when the .refcount of a zval turns to 0. > I'm using 5.2.2. For example I > see the following results when profiling: > > Memory: 256 KB > Load a 1024x768 JPEG (via GD) > Memory: 4 MB > Create thumbnail (via GD) > Memory: 5.2 MB > Destroy original image resource (imagedestroy) Try unset($image) as well, so PHP "knows" you no longer need access to that variable that was holding all that stuff... > Memory: 5.2 MB > > I would have expected (or rather, hoped) that the memory use would > have dropped down quite dramatically after destroying the image > resource that was using up nearly 4MB of memory, but it didn't seem to > change. How are you measuring this? What version of PHP? The Memory Manager changed over the course of time. I'm also not at all sure that you *can* measure it as precisely as you are trying to do. > Is this a limitation of the memory_get_usage(true) function, or does > imagedestroy not actually do what it implies? Almost for sure imagedestroy() does what it should -- and GD frees up the internal memory structures for that image. PHP still has a variable sitting around pointing to that resource, however, and you may need to notify PHP through unset() that you are "done" with it. That said: PHP doesn't really allocate that 5.2M of RAM. GD does. PHP may not be able to tell you accurately about what GD is doing internally -- but it's probably not *really* losing that 5.2M or you'd hear an awful lot more screaming about it from all quarters. :-) -- Some people have a "gift" link here. Know what I want? I want you to buy a CD from some indie artist. http://cdbaby.com/browse/from/lynch Yeah, I get a buck. So?