_BLOCK_TYPE_IS_VALID（pHead-> nBlockUse）在C ++中崩溃

Question

I have a Qt GUI program, inside it I could click a button to load/unload many dock widgets. I have the problem that when I click the button to load/unload dock widgets, the programm crash with saying that

Debug Assertion Failed, Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

It doesn't happen every time. (Actually very rare to happen.) And when I check the Windows's event log, it says the application hang with a cross thread dead lock. But most people online said that the _BLOCK_TYPE_IS_VALID(pHead->nBlockUse) means a memory error. I just don't what's going on...

It is a very big program by someone else and the bug happens very rarely... What I could do now to locate the bug?

EDIT: Hi, I have got the crash dump file, and I have seen that my program stop at a worker thread with the call stack: > ntdll.dll!_NtWaitForMultipleObjects@20() + 0x15 bytes
How could I trace back to the source code that the program actually stop?

Answer 1

That usually means you're trying to access an illegal memory block inside an std container.

To debug this properly, just look at the stack in the Call Stack window, look up the stack until you get to your code, and see why the value is invalid.

Answer 2

It's hard to describe it, but briefly, here is what you should do:

Install Application Verifier and run it.

Ctrl+A , select your executable.

Deselect all tests in the right pane, select only Basic->Heaps.

Ensure you have 'Full heap' enabled and 'Traces' enabled (properties via right click on 'Heaps' item).

Save. You may close Application Verifier now.

Launch WinDBG of proper architecture (the same as your app).

Ctrl+E , select your executable.

The program will be stopped on first instruction, run it using F5

The probability you'll hit the bug will be much higher. You'll also may found memory access issue you were not aware of before. When you hit one of them, the debugger will stop with one of 'Verifier stops' and you'll see the message in console telling you which command you can use to investigate further. Usually you'll be able to see detailed info about the heap using !heap -p -a <address> , including allocation and deallocation stacks.

Remember, that Application Verifier checks are enabled even when Application Verifier application is not started. You need to run Application Verifier, disable the checks and press 'Save' to actually disable them.

Hope this will help, at least a bit. Read more about Application Verifier techniques on the Internet.