Is my memory leaking? Part1.

by - 12:45

There often appear posts on the Open CASCADE forum, either as questions or as blames that there are persistent memory leaks. Truth to be told, this happens on many forums of other software products I visited, so this is not something OCC-specific.
So I'd like to shed some light, which would hopefully help someone to understand the issue in the future. As always, extensions and any comments are welcome.

So how one detects there is a memory leak? I would suggest the following possibilities (presumably in the order of decreasing frequency of use by developers):

Using Visual Studio built-in features
(I never use these though).
Put the following lines in the source file or your executable:

#include <stdlib.h>
#include <crtdbg.h>

And into the main() function:

For more information you can read this MSDN page (select appropriate VS version).

Under the debugger, in the Output window you will see something like:

Detected memory leaks!
Dumping objects ->
{35171} normal block at 0x04CD0068, 260 bytes long.
Data: < > 02 00 00 00 00 00 00 00 CD CD CD CD CD CD CD CD
{349} normal block at 0x0330E350, 100 bytes long.
{246} normal block at 0x03309390, 108 bytes long.
Data: < E ( > 01 00 00 00 1A 00 00 00 45 01 00 00 28 0A 00 00

Once you see this you might find yourself yelling – "how may this !@#$% product exist with such fundamental bugs ?!!". But as soon as you see this attributes to your code, you may go "hmm, is this really an error?" As you start digging deeper, things may go different ways. You may discover a bug in your product or a tool limitation (the latter is more likely though).

Windows Task Manager
You notice the level of consumed memory before you start some piece of your code (e.g. opening a document in an MDI application).

MDI app memory level before opening a document

Then do some actions and see the new level. For instance, after closing the document in the MDI app, you would expect the level returns to a previous one. If not (and as a rule, not!) you start asking why.

Same app memory level after closing an opened document

Specialized memory checking tools
This includes Valgrind, Bounds Checker (never used those two), Rational Purify, Intel Parallel Inspector XE, etc. I used Purify in late 1990es and as of 2008 sticked to Intel Inspector. Here is a sample report generated by Inspector:

Intel Parallel Inspector XE reporting memory leaks

You can try an evaluation version on the Intel site here.

Debug print
Adding simple outputs in constructor and destructor is simple yet effective practice to quickly check if your object is destroyed whenever you expect.

Custom memory checkers/profilers
You might want to write some ad-hoc memory profiler – some hooks that trace allocation and deallocation routines (malloc/free, new/delete) – counting allocated and deallocated bytes. I myself created one when tracing memory in CAD Exchanger. If there is sufficient interest, I could publish it. The idea is to detect pieces of code where you expect that all allocated memory during that region will be deallocated upon its end.

(to be continued...)

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