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Detecting memory leaks with Windbg
From time to time I like to use Windbg to look into memory leaks, if only to get a hang of and familiarize myself with the `!heap` extension. Along the way I ran into an option that I never noticed before: -l. The docs say:
======================
The !heap -l command detects leaked heap blocks. It uses a garbage collector algorithm to detect all busy blocks from the heaps that are not referenced anywhere in the process address space. For huge applications, it can take a few minutes to complete. This command is only available in Windows XP and later versions of Windows.
======================
If I were to break into the debugger at random points (of course, I am supposed to have used: gflags.exe /i +ust MyApp.exe prior to doing all this) and run !heap -l, I see a whole bunch of callstacks leading up to some memory allocations. Do I take it to mean all these are allocations that were never freed? IOW, I am not sure I understand the "busy blocks not referenced anywhere in the process space" comment.
======================
The !heap -l command detects leaked heap blocks. It uses a garbage collector algorithm to detect all busy blocks from the heaps that are not referenced anywhere in the process address space. For huge applications, it can take a few minutes to complete. This command is only available in Windows XP and later versions of Windows.
======================
If I were to break into the debugger at random points (of course, I am supposed to have used: gflags.exe /i +ust MyApp.exe prior to doing all this) and run !heap -l, I see a whole bunch of callstacks leading up to some memory allocations. Do I take it to mean all these are allocations that were never freed? IOW, I am not sure I understand the "busy blocks not referenced anywhere in the process space" comment.
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Comments
process address space. If the address is not found then it is shown as
"leaking". I think "busy" blocks also include freed allocations present in
the front-end allocator, so this may not necessarily be a leak. If it is
your code check from code review if the stacks shown in !heap -l are
actually leaking.
On Thu, Nov 2, 2017 at 2:46 AM, [email protected]
wrote:
> From time to time I like to use Windbg to look into memory leaks, if only
> to get a hang of and familiarize myself with the `!heap` extension. Along
> the way I ran into an option that I never noticed before: -l. The docs say:
>
> ======================
> The !heap -l command detects leaked heap blocks. It uses a garbage
> collector algorithm to detect all busy blocks from the heaps that are not
> referenced anywhere in the process address space. For huge applications, it
> can take a few minutes to complete. This command is only available in
> Windows XP and later versions of Windows.
> ======================
>
> If I were to break into the debugger at random points (of course, I am
> supposed to have used: gflags.exe /i +ust MyApp.exe prior to doing all
> this) and run !heap -l, I see a whole bunch of callstacks leading up to
> some memory allocations. Do I take it to mean all these are allocations
> that were never freed? IOW, I am not sure I understand the "busy blocks not
> referenced anywhere in the process space" comment.
>
>
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