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Asked: 2026-06-13T07:17:05+00:00

I have a handle leak in a C# program. I’m trying to diagnose it

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I have a handle leak in a C# program. I’m trying to diagnose it using WinDbg using !htrace, roughly as presented in this answer, but when I run !htrace -diff in WinDbg I’m presented with stack traces that don’t show the names of my C# functions (or even my .net assembly).

I created a small test program to illustrate my difficulty. This program does nothing except “leak” handles.

class Program
{
    static List<Semaphore> handles = new List<Semaphore>();

    static void Main(string[] args)
    {
        while (true)
        {
            Fun1();
            Thread.Sleep(100);
        }
    }

    static void Fun1()
    {
        handles.Add(new Semaphore(0, 10));            
    }
}

I compiled the assembly, and then in WinDbg I go “File” -> “Open Executable” and select my program (D:\Projects\Sandpit\bin\Debug\Sandpit.exe). I continue program execution, break it, and run “!htrace -enable”, then continue for a bit longer, and then break and run “!htrace -diff”. This is what I get:

0:004> !htrace -enable
Handle tracing enabled.
Handle tracing information snapshot successfully taken.
0:004> g
(1bd4.1c80): Break instruction exception - code 80000003 (first chance)
eax=7ffda000 ebx=00000000 ecx=00000000 edx=77b2f17d esi=00000000 edi=00000000
eip=77ac410c esp=0403fc20 ebp=0403fc4c iopl=0         nv up ei pl zr na pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00000246
ntdll!DbgBreakPoint:
77ac410c cc              int     3
0:004> !htrace -diff
Handle tracing information snapshot successfully taken.
0xd new stack traces since the previous snapshot.
Ignoring handles that were already closed...
Outstanding handles opened since the previous snapshot:
--------------------------------------
Handle = 0x00000250 - OPEN
Thread ID = 0x00001b58, Process ID = 0x00001bd4

0x77ad5704: ntdll!ZwCreateSemaphore+0x0000000c
0x75dcdcf9: KERNELBASE!CreateSemaphoreExW+0x0000005e
0x75f5e359: KERNEL32!CreateSemaphoreW+0x0000001d
*** WARNING: Unable to verify checksum for C:\Windows\assembly\NativeImages_v4.0.30319_32\System\13c079cdc1f4f4cb2f8f1b66c8642faa\System.ni.dll
0x65d7e805: System_ni+0x0020e805
0x65d47843: System_ni+0x001d7843
0x65d477ef: System_ni+0x001d77ef
0x004700c9: +0x004700c9
0x67d73dd2: clr!CallDescrWorkerInternal+0x00000034
0x67d9cf6d: clr!CallDescrWorkerWithHandler+0x0000006b
0x67d9d267: clr!MethodDescCallSite::CallTargetWorker+0x00000152
0x67eb10e0: clr!RunMain+0x000001aa
0x67eb1200: clr!Assembly::ExecuteMainMethod+0x00000124
--------------------------------------
Handle = 0x0000024c - OPEN
Thread ID = 0x00001b58, Process ID = 0x00001bd4

0x77ad5704: ntdll!ZwCreateSemaphore+0x0000000c
0x75dcdcf9: KERNELBASE!CreateSemaphoreExW+0x0000005e
0x75f5e359: KERNEL32!CreateSemaphoreW+0x0000001d
0x65d7e805: System_ni+0x0020e805
0x65d47843: System_ni+0x001d7843
0x65d477ef: System_ni+0x001d77ef
0x004700c9: +0x004700c9
0x67d73dd2: clr!CallDescrWorkerInternal+0x00000034
0x67d9cf6d: clr!CallDescrWorkerWithHandler+0x0000006b
0x67d9d267: clr!MethodDescCallSite::CallTargetWorker+0x00000152
0x67eb10e0: clr!RunMain+0x000001aa
0x67eb1200: clr!Assembly::ExecuteMainMethod+0x00000124
...
--------------------------------------
Displayed 0xd stack traces for outstanding handles opened since the previous snapshot.

As you can see, the stack trace is missing my C# function names “Main” and “Fun1”. I believe “System_ni+0x…” frames may be my function frames, but I don’t know. My question is, how do I get WinDbg to display function names for my C# functions in the stack trace?

Extra information:
My WinDbg symbol search path is

SRVC:/symbolshttp://msdl.microsoft.com/download/symbols;D:\Projects\Sandpit\bin\Debug;srv*

I don’t get any errors when I open the executable in WinDbg. There is a file called “Sandpit.pdb” in the output directory (“D:\Projects\Sandpit\bin\Debug”). The project is built locally so the pdb file should match the exe. I downloaded WinDbg from here. I have “Enable native code debugging” checked in the project settings in Visual Studio.

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1 Answer

  1. Editorial Team

    WinDbg attempts to interpret the native call stack as best it can, however to fully interpret the stack of a CLR application WinDbg needs to use an extension called SOS. This extension has a separate command CLRStack for viewing the stack information of CLR stacks. You will need to load the SOS extension first however using the .loadby sos clr command (or similar, I remember getting the correct version SOS to load could be a bit of a pain)

    For more information see

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