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How can .NET threads be waiting on a syncblk which is not owned by any thread?

Asked 2011-10-19T17:32:53.520
11

I have a crash dump from my app showing a bunch of threads waiting on a syncblk, and the syncblk shows that it has no owning thread. How is that possible? I'm trying to reproduce the symptom in a test app, and I can't figure out what could possibly happen to produce that result....having the owning thread exit or die without releasing the syncblk still shows up as owning the object, just the threadid is "XXX"....I've tested using fully managed graceful exit and hard thread termination via pinvoke....I tested a bunch of different combinations of waits without pulses, mismatched enters and exits...nothing produces a syncblk which blocks threads and shows no owner.....I'm running out of ideas

Here is the output from my crashdump that I'm trying to replicate: (Note index #1236)

0:000> !syncblk
Index         SyncBlock MonitorHeld Recursion Owning Thread Info          SyncBlock Owner
 784 0000000004f12eb0            3         1 000000000508a460  32a8  68   00000001a0a20510
 966 0000000004f06928            1         1 00000000052c5da0  2380 114   00000001df3080f8
1085 0000000004f23088            1         1 00000000052c8080  496c 120   00000001a0325238
1144 0000000005160d20            1         1 00000000050968b0   d74  56   00000000ff61b570
1151 0000000004f0c2c8            1         1 000000000508d8b0  3f64  77   000000017f66dc20
1236 0000000004f0b4f8           16         0 0000000000000000     none    000000019f1ec5d8
1261 0000000004f0ffe8            1         1 0000000008f18fc0  446c  94   000000013f8e70b0
1306 0000000004f0e918            1         1 00000000052c91f0  406c 123   000000011f5936f8
1318 0000000004f0e528            3         1 0000000008f1d580  24d8 106   000000015fc73f28
1329 0000000004f0cc58            1         1 0000000005095740  2fbc  53   000000011f36d320
1332 0000000004f15b38            1         1 0000000008f16710  3804  87   000000019f964728
1387 0000000004f22350            1         1 0000000008f18420  5180  92   00
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Possibility 1: The syncblk is cleared and the next of the 16 threads will grab it as soon as it is scheduled again. Possibility 2: You have corrupt memory.

answered 2011-10-19T17:47:42.353

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