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windbg a .net core 3.1 app memory leak

gsferreira profile image Guilherme Ferreira Originally published at gsferreira.com on ・2 min read

I've spent the past few days trying to fix a memory leak. I was having problems to figure out what was leaking, so I used windbg wishing that it would help me.

I confess that I'm not an experienced user of windbg, so I google how to catch memory issues using windbg. There's a ton of information out there. The problem is that I didn't found a guide on how to do it with a .net core application.

So, I'm sharing here how I've done it:

  1. Install windbg (see here).
  2. Add windbg.exe (x64 version) to your environment path.
  3. Install SOS (see here): dotnet tool install -g dotnet-sos.
  4. Set breakpoint(s) using System.Diagnostics.Debugger.Break() in your source code.
  5. Update your project (*.csproj file) to Load Symbols: <DebugSymbols>true</DebugSymbols><DebugType>pdbonly</DebugType>.
  6. Build your project using Release configuration: dotnet build -c Release.
  7. Launch with WinDbg attached to your project: windbg dotnet [YOUR DLL PATH].dll.
  8. Load SOS using .load C:\Users\[USERNAME]\.dotnet\sos\sos.dll ..

windbg - load sos

  1. Enter g to go to the first breakpoint.
  2. Enter !gchandles to see garbage collector handles.
  3. !DumpHeap /d -mt [MT] using the memory type id from the result list of the previous command. Example: !DumpHeap /d -mt 00007ffb4c85ca98
  4. !gcroot -all [ADDRESS] using the memory address form the result list of the previous command. Example: !gcroot -all 0x0000023cd2e71510

Following this guide, you should have a clue of what is still in memory and where the object is in use.

Hope this helps.

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