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How to troubleshot native memory leaks on Windows: GFlags and UMDH
Memory issues are amongst the worst one to solve because pointing precisely the source is often difficult and painful. Memory leaks are not an exception, especially with real-world application: most of the time, programmers start to worry about it when the application outputs some “out of memory” errors. At this moment, you have to find which one, among thousands of functions and many more allocated blocks, causes the application to leak and eventually to crash.
Let’s summarize what you really need when you have a memory leak (in addition to a way to reproduce the issue):
- You want to find which object(s) are leaking
- You want to know why they are leaking: is there some static reference to it, or maybe they are not freed?
The process described today deals with the first one, which is often the most difficult.
Who the hell killed my process?
There is a few reasons that can make a process disappear. It can be:
- a normal termination (you reach the end of the main function)
- a call to ExitProcess, potentially located anywhere in your code
- an exception walking up all through the call stack of its thread, making the process die.
How to debug a process as soon as it starts with WinDbg or Visual Studio 2010
Sometimes bug happens before you have the chance to attach a debugger to the faulting process. Most of the time it’s because it is launched by another process (a service, the compiler used to create a Xml serializer of a .NET software, a batch script, etc.) and you don’t have the time to get the command line with ProcessExplorer. And even if you can get it, a process may expect some context coming from its parent. And obviously, sometimes you don’t have a clue about how a process is launched, all you know is that it crashes and you need to see what’s inside before it do so.
After a few tryout to pause the process (Process Explorer is your friend) before it crashes, or some tentative to slow down your computer so you have the time to attach a debugger, you’re starting to get frustrated. Hopefully I have some solutions for you.
How to debug a Windows service
Maybe you thought when you read this title: “well it’s kind of easy, I just have to attach any debugger to my running service“. And you’re definitely right.
But sometimes you have to debug the very beginning of your service (just after the “Start” control), or even before, when the main() function has just started. Or you’re experiencing a bug that happens only with a specific user, or only in a context of a Windows service (could be environment variables, registry keys, etc.). Hopefully, with a few tricks, you can easily setup a debugger that will attach to a process just after its creation.
BugSlasher 