CODEWITHSUNDEEP
windbg
John Vottero
John Vottero

Reputation: 925

syncblk with odd MonitorHeld count and no owner

I have found a number of posts that talk about syncblk output that shows an even number for the MonitorHeld count and no owner thread. This has been explained as a quirk, the lock is in transition probably because the owner thread has failed so, there is no owner. The MonitorHeld count is incremented by 2 for each waiter and one for the owner so, an even number means you have waiters but no owner.

My syncblk shows an odd number for the MonitorHeld count yet, no owning thread. What does that indicate? Also, I have two different process dumps from two different instances that look like this so, it wasn't a case of capturing a dump at just the right time.

My syncblk output:

Index         SyncBlock MonitorHeld Recursion Owning Thread Info          SyncBlock Owner
  164 000000000a4d2428            1         1 000000002e406d30 16ac 144   0000000012f107c0 System.Object
  368 000000000a3eb378         1125         0 0000000000000000     none    00000000104b1a38 System.Object
  401 000000000a4d2888            1         1 000000002e79cce0 21a0 123   00000000110b09b0 System.Object
  505 000000000a516918            1         1 000000002e55ca70 95c 114   00000000110984f0 System.Object
  563 0000000002ae7978            1         1 000000002e7e1910 2058 261   00000000127d0300 System.Object
  678 0000000002ae7f18            3         1 000000000a462240 f44 156   0000000012a66a28 System.Object
-----------------------------
Total           814
CCW             0
RCW             1
ComClassFactory 0
Free            142

Index         SyncBlock MonitorHeld Recursion Owning Thread Info          SyncBlock Owner
  122 000000002e561d98            3         1 000000000a621400 1410 180   0000000012cfcf28 System.Object
  164 000000000a4d2428            1         1 000000002e406d30 16ac 145   0000000012f107c0 System.Object
  368 000000000a3eb378          951         0 0000000000000000     none    00000000104b1a38 System.Object
  401 000000000a4d2888            1         1 000000002e79cce0 21a0 124   00000000110b09b0 System.Object
  505 000000000a516918            1         1 000000002e55ca70 95c 115   00000000110984f0 System.Object
  563 0000000002ae7978            1         1 000000002e7e1910 2058 263   00000000127d0300 System.Object
-----------------------------
Total           814
CCW             0
RCW             20
ComClassFactory 0
Free            76

Upvotes: 2

Views: 712

Answers (1)

Steve Johnson
Steve Johnson

Reputation: 3027

The lock is either in transition or orphaned. A SyncBlk is orphaned when the owning thread terminates without releasing it.

Upvotes: 2

Related Questions