windbg - C# Monitor Lock을 획득하고 있는 스레드 찾는 방법
이에 대해서는 다음의 글에 방법이 잘 나옵니다.
Analyzing Monitor-Based Deadlocks with SOS.dll
; http://blogs.microsoft.co.il/sasha/2009/10/17/analyzing-monitor-based-deadlocks-with-sosdll/
그런데 직접 실습을 해보니 약간 달라진 면이 있어서 기록을 남깁니다.
우선, 재현을 위해 간단한 테스트 프로그램을 다음과 같이 만들어 볼 수 있습니다.
using System;
using System.Threading;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
object _objLock1 = new object();
object _objLock2 = new object();
Thread t1 = new Thread(threadFunc1);
t1.IsBackground = true;
t1.Start(_objLock1);
Thread t2 = new Thread(threadFunc2);
t2.IsBackground = true;
t2.Start(_objLock2);
lock (_objLock1)
lock (_objLock2)
{
Console.WriteLine("Enter...");
Console.ReadLine();
Console.WriteLine("Exit...");
}
}
private static void threadFunc1(object obj)
{
lock (obj)
{
Console.WriteLine("threadFunc1");
}
}
private static void threadFunc2(object obj)
{
lock (obj)
{
Console.WriteLine("threadFunc2");
}
}
}
}
결국, Main 스레드가 2개의 lock을 이미 소유한 상태에서 threadFunc1과 threadFunc2의 실행이 hang 상태가 된 것을 표현한 것입니다.
위의 프로그램을 실행하고 작업 관리자를 이용해 덤프를 남긴 후 windbg로 읽어들입니다. 당연히 ".loadby sos clr"로 sos 확장을 로드하고 다음과 같이 현재 열려 있는 lock의 수를 확인할 수 있습니다.
0:000> !syncblk
Index SyncBlock MonitorHeld Recursion Owning Thread Info SyncBlock Owner
3 0000027ecd80ece8 3 1 0000027ecd7b2b00 7744 0 0000027ecf3a3ea8 System.Object
4 0000027ecd80ed38 3 1 0000027ecd7b2b00 7744 0 0000027ecf3a3ec0 System.Object
-----------------------------
Total 4
CCW 0
RCW 0
ComClassFactory 0
Free 0
보는 바와 같이 총 2개의 lock이 사용 중이고, 현재 그것을 점유하고 있는 "Owing Thread"는 0000027ecd7b2b00으로 나옵니다. 이에 해당하는 스레드 정보는 !threads 명령어로 확인할 수 있습니다.
0:000> !threads
ThreadCount: 4
UnstartedThread: 0
BackgroundThread: 3
PendingThread: 0
DeadThread: 0
Hosted Runtime: no
Lock
ID OSID ThreadOBJ State GC Mode GC Alloc Context Domain Count Apt Exception
0 1 7744 0000027ecd7b2b00 2a020 Preemptive 0000027ECF3A9FA8:0000027ECF3A9FD0 0000027ecd783180 3 MTA
5 2 44c0 0000027ecd7dbe40 2b220 Preemptive 0000000000000000:0000000000000000 0000027ecd783180 0 MTA (Finalizer)
6 3 7d7c 0000027ecd80e470 202b220 Preemptive 0000027ECF3A6018:0000027ECF3A7FD0 0000027ecd783180 0 MTA
7 4 1338 0000027ecd814970 202b220 Preemptive 0000000000000000:0000000000000000 0000027ecd783180 0 MTA
0번 스레드인데 당연히 Main 메서드를 실행 중일 테니 굳이 확인할 필요도 없어 보입니다.
나머지 중에 5번 스레드는 Finalizer고 6번과 7번이 우리가 생성했던 스레드였을 텐데 이 중에서 6번을 먼저 살펴보겠습니다.
0:000> ~6s
ntdll!NtWaitForMultipleObjects+0x14:
00007fff`499f5ef4 c3 ret
0:006> !clrstack
OS Thread Id: 0x7d7c (6)
Child SP IP Call Site
000000e3b82ff0f8 00007fff499f5ef4 [GCFrame: 000000e3b82ff0f8]
000000e3b82ff238 00007fff499f5ef4 [GCFrame: 000000e3b82ff238]
000000e3b82ff278 00007fff499f5ef4 [HelperMethodFrame_1OBJ: 000000e3b82ff278] System.Threading.Monitor.Enter(System.Object)
000000e3b82ff370 00007ffed33f0775 ConsoleApp1.Program.threadFunc1(System.Object) [E:\ConsoleApp1\ConsoleApp1\Program.cs @ 32]
000000e3b82ff3c0 00007fff2f06ca72 System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
000000e3b82ff490 00007fff2f06c904 System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
000000e3b82ff4c0 00007fff2f06c8c2 System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
000000e3b82ff510 00007fff2fa40ffc System.Threading.ThreadHelper.ThreadStart(System.Object)
000000e3b82ff768 00007fff329f6753 [GCFrame: 000000e3b82ff768]
000000e3b82ffab8 00007fff329f6753 [DebuggerU2MCatchHandlerFrame: 000000e3b82ffab8]
콜스택 상단에 Monitor.Enter가 있으므로 현재 lock을 대기 중임을 알 수 있습니다. 그렇다면 어떤 object를 대상으로 lock을 건 것일까요? 이를 위해 native 레벨의 callstack을 확인해 보면 단서를 찾을 수 있습니다.
0:006> kv
# Child-SP RetAddr : Args to Child : Call Site
00 000000e3`b82feb38 00007fff`4677dd20 : 00000099`00000000 00000000`00000010 00000002`00000002 00007fff`00000010 : ntdll!NtWaitForMultipleObjects+0x14
01 000000e3`b82feb40 00007fff`32bb401e : ffffffff`fffffffe 00007fff`00000000 000000e3`b82ff0f8 00000000`00000000 : KERNELBASE!WaitForMultipleObjectsEx+0xf0
02 000000e3`b82fee40 00007fff`32bb3eb0 : 00000000`00000001 00000000`00000000 0000027e`cd80e470 00000000`ffffffff : clr!WaitForMultipleObjectsEx_SO_TOLERANT+0x62
03 000000e3`b82feea0 00007fff`32bb3ca9 : 0000027e`cd80e470 00000000`00000001 00000000`00000000 00007ffe`00000000 : clr!Thread::DoAppropriateWaitWorker+0x1e4
04 000000e3`b82fefa0 00007fff`32bb42b9 : 00000000`00000000 00007fff`00000001 0000027e`cd80e470 00007fff`329ff1af : clr!Thread::DoAppropriateWait+0x7d
05 000000e3`b82ff020 00007fff`32bb458e : 0000027e`cd80ece8 000000e3`b82ff3b0 00000000`00000000 0000027e`cd80e470 : clr!CLREventBase::WaitEx+0xc4
06 000000e3`b82ff0b0 00007fff`32bb44a2 : 0000027e`cd80ece8 0000027e`cd80ece8 00007ffe`00000000 0000027e`cf3a3ea8 : clr!AwareLock::EnterEpilogHelper+0xca
07 000000e3`b82ff170 00007fff`32bb41b2 : 0000027e`cd80e470 0000027e`cd80e470 00000000`00000000 0000027e`cd80ece8 : clr!AwareLock::EnterEpilog+0x62
08 000000e3`b82ff1d0 00007ffe`d33f0775 : 0000027e`cf3a3fa0 000000e3`b82ff3a8 0000027e`cf3a4080 00000000`00000000 : clr!JITutil_MonEnterWorker+0xe2
09 000000e3`b82ff370 00007fff`2f06ca72 : 0000027e`cf3a3ea8 0000027e`cf3a3ea8 000000e3`b82ff3f0 00000000`00000000 : 0x00007ffe`d33f0775
0a 000000e3`b82ff3c0 00007fff`2f06c904 : 0000027e`cf3a4080 0000027e`cf3a3fa0 0000027e`cf3a3f78 00000000`00000000 : mscorlib_ni+0x4dca72
0b 000000e3`b82ff490 00007fff`2f06c8c2 : 0000027e`cf3a3f78 00000000`00000000 00000000`cf3a3ea8 00000000`00000000 : mscorlib_ni+0x4dc904
0c 000000e3`b82ff4c0 00007fff`2fa40ffc : 000000e3`b82ff668 000000e3`b82ff668 000000e3`b82ff570 00000000`00000000 : mscorlib_ni+0x4dc8c2
0d 000000e3`b82ff510 00007fff`329f6753 : 0000027e`cf3a3fe0 0000027e`cf3a3ea8 00000000`00000000 00000000`00000000 : mscorlib_ni+0xeb0ffc
0e 000000e3`b82ff550 00007fff`329f6649 : 00000000`00000001 00007fff`32b3f8e3 000000e3`b82ff828 00000000`00000000 : clr!CallDescrWorkerInternal+0x83
0f 000000e3`b82ff590 00007fff`329f732d : 00000000`00000002 000000e3`b82ff748 000000e3`b82ff768 000000e3`b82ff828 : clr!CallDescrWorkerWithHandler+0x4e
10 000000e3`b82ff5d0 00007fff`32b096e9 : 000000e3`b82ffbe0 000000e3`b82ffb20 00007fff`2f28e720 000000e3`b82ffb20 : clr!MethodDescCallSite::CallTargetWorker+0xf8
11 000000e3`b82ff6d0 00007fff`329f7c9d : 00000000`00001f80 00007fff`32b095e0 000000e3`b82ffb20 ffffffff`ffffffff : clr!ThreadNative::KickOffThread_Worker+0x109
12 000000e3`b82ff930 00007fff`329f7c18 : 000000e3`b82ffb20 00007fff`329f6051 0000027e`00000000 00000000`00000018 : clr!Frame::Push+0x59
13 000000e3`b82ff970 00007fff`329f7b56 : 00000000`00000001 00000000`00000000 00000000`00000000 00000000`00000000 : clr!MarshalInfo::SetupArgumentSizes+0x234
14 000000e3`b82ffa70 00007fff`329f7cdf : ffffffff`ffffffff 0000027e`cd80e470 0000027e`cd80e470 0000027e`cd806190 : clr!MarshalInfo::SetupArgumentSizes+0x15d
15 000000e3`b82ffb00 00007fff`32b095cb : 0000027e`cd80e470 000000e3`00000001 0000027e`cd806190 00000000`00000003 : clr!MarshalInfo::SetupArgumentSizes+0xe3
16 000000e3`b82ffb60 00007fff`32b31c3f : 0000027e`cd806190 0000027e`cd80e470 000000e3`b82ffbb8 00000000`00000000 : clr!ThreadNative::KickOffThread+0xdb
17 000000e3`b82ffc30 00007fff`47152774 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : clr!Thread::intermediateThreadProc+0x86
18 000000e3`b82ffd70 00007fff`499c0d51 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : kernel32!BaseThreadInitThunk+0x14
19 000000e3`b82ffda0 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : ntdll!RtlUserThreadStart+0x21
콜스택에 보면 clr!CLREventBase::WaitEx 호출이 보이는데 그것의 첫 번째 인자(0000027e`cd80ece8) 값이 바로 syncblock 값과 일치하게 나옵니다.
0:000> !syncblk
Index SyncBlock MonitorHeld Recursion Owning Thread Info SyncBlock Owner
3 0000027ecd80ece8 3 1 0000027ecd7b2b00 7744 0 0000027ecf3a3ea8 System.Object
4 0000027ecd80ed38 3 1 0000027ecd7b2b00 7744 0 0000027ecf3a3ec0 System.Object
즉, 6번 스레드는 0000027ecd80ece8에 해당하는 lock을 대기하고 있는 중이며 그 lock을 현재 소유하고 있는 스레드는 0000027ecd7b2b00인 0번 스레드임이 밝혀집니다. 이 정도면... ^^ 실전에서 충분히 추적할만한 단서가 되겠지요.
[이 글에 대해서 여러분들과 의견을 공유하고 싶습니다. 틀리거나 미흡한 부분 또는 의문 사항이 있으시면 언제든 댓글 남겨주십시오.]