Thursday, June 12, 2008

Tablet Python #4 - Sources of Memory Leaks

Marius Gedminas blogged an interesting article about memory leaks in Python. On the tablet you don't have much memory available, so memory leaks will annoy the users very quickly.

Python is a garbage-collected language (like Java or C#), so memory leaking is normally not an issue, but there are situations where you should be careful.

Bindings to C libraries

Many modules are bindings to C or C++ libraries, and memory leaking is unfortunately quite common in those languages, esp. in complex libraries. A hot candidate for memory leaking on the maemo platform are the GdkPixbuf operations.

GdkPixbufs get not automatically garbage collected by Python. Always use del on a GdkPixbuf explicitly when you don't need it any longer.

The __del__ destructor method

Classes can have some sort of destructor method in Python.

def __del__(self):


This is called when you use del on the last reference you are holding. But be very careful! Classes overriding this destructor method are not eligible for breaking reference cycles by the garbage collector anymore! They have to be released manually. It's normally not necessary to override the __del__ method, so you better stay away from it.

Always take special care when dealing with classes overriding the __del__ method. Cyclic references involving such classes cannot be resolved by the garbage collector automatically.