This document discusses techniques for debugging .NET applications using memory dumps. It describes how to generate memory dumps using Task Manager, ProcDump, and Debug Diagnostics. It then explains how to analyze dumps using WinDbg, Debug Diagnostics, and Visual Studio. Specific issues covered include crashes, performance problems, and memory leaks. Automated analysis of dumps is demonstrated using CLRMD.

1. .NET
DEBUGGING
@TessFerrandez
Microsoft

2. Crashes
Performance Issues
Memory Leaks
Issues that we can’t step by step debug
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3. MEMORY
DUMPS

4. User-mode dump
Snapshot of a process and the memory
it addresses
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5. Threads call stacks, stack objects
Modules dlls, exes
.NET Heap .net objects, sizes, info
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6. GATHERING
MEMORY DUMPS

7. TASK MANAGER
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8. PROCDUMP
Light-weight, no-install utility for generating
dumps
Procdump –ma app.exe app.dmp
Procdump –ma –h app.exe hang.dmp
Procdump –ma –e app.exe crash.dmp
Procdump –ma –c 90 app.exe cpu.dmp
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9. DEBUG DIAG
GUI tool to generate dumps based on rules
and analyze dumps for common .net issues
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10. ANALYZING
MEMORY DUMPS

11. WINDBG
Native debugger
Installed with WDK and Debugging tools for
Windows
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12. @TessFerrandez
DEBUG DIAG

13. VISUAL STUDIO
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14. CRASHES

15. When I open an email with a pdf attachement that is
larger than 2 MB, a message box saying Unknown Error
shows up and then the process exits
Tess!!! the internet e-thingy is not working anymore

16. WHO
DUNNIT?
Unhandled Exception – 2nd chance
StackOverflowException
OutOfMemoryException
ExecutionEngineException
Kill or recycle

17. 1 Check the event viewer
2 Capture dump on crash
3 Look at the faulting stack
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18. PERFORMANCE
ISSUES

19. App is not responding
Requests take too long
How long should they take?
CPU is going hey-wire

20. WHO
DUNNIT?
LOW CPU
Waiting for an external resource
Deadlock
HIGH CPU
Busy, Tight loop
High CPU in GC

21. 1 Determine if it is high or low CPU
2 Capture one or more dumps
3 Look at all stacks
If you can repro in test, consider profiling
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22. MEMORY
LEAKS

23. OutOfMemoryExceptions
Slow response times
Due to GC activities
Memory increase in perfmon or task manager

24. WHO
DUNNIT?
Cache or Session State
Static / Pinned
Blocked Finalizer
Assembly Leak
Native Leak

25. 1 Capture multiple dumps
2 Compare to see what objects are leaking
3 Find out why they are still around
For native leaks, use leaktracking in debug diag
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26. AUTOMATION

27. CLRMD
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28. DataTarget target = DataTarget.LoadCrashDump(@"TheApp.dmp");
target.SymbolLocator.SymbolCache = @"c:symbols";
target.SymbolLocator.SymbolPath = "http://msdl.microsoft.com/download/symbols";
var runtime = target.ClrVersions[0].CreateRuntime();
Console.WriteLine("Is Server GC: {0}", runtime.ServerGC);
Console.WriteLine("Number of heaps: {0}", runtime.HeapCount);
Console.WriteLine("Number of threads: {0}", runtime.Threads.Count);
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29. foreach (var thread in runtime.Threads) {
var e = thread.CurrentException;
if (e != null) {
Console.WriteLine("Thread {0}", thread.ManagedThreadId);
Console.WriteLine("t{0} - {1}", e.Type.Name, e.Message);
foreach (var frame in e.StackTrace) {
Console.WriteLine("t" + frame.DisplayString);
}
}
}
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30. .NET
DEBUGGING
@TessFerrandez
Microsoft