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Asked: 2026-05-13T17:31:54+00:00

I am looking of a description of the output generated by the !SyncBlk command

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I am looking of a description of the output generated by the !SyncBlk command of SOS.

Particularly I found no useful explanation on the column “MonitorHeld”. This column shows high values in a series of crash dumps.

Example:

0:000> !SyncBlk
Index         SyncBlock MonitorHeld Recursion Owning Thread Info          SyncBlock Owner
   44 0000000005a5c228            1         1 000000000e7a6740  2304 273   000000019f858cd0 System.Object
   48 000000000579bae8            1         1 000000000e7a72e0  2370 275   000000015f999900 System.Object
   52 000000000579b9c8            1         1 0000000011bbd3b0  1e98 295   00000000ff89fe08 System.Object
   54 000000000579b938            1         1 000000000e7a38c0  1be4 249   000000013f8aa888 System.Object
  108 0000000005a5bfe8            1         1 000000000e79f300  224c 242   00000000ff8a5828 System.Object
  110 0000000005a5c078            1         1 000000000e79ca50  2290 262   000000015f9a8020 System.Object
  112 0000000005a5c108            1         1 0000000011bb70e0  1d38 236   000000015f99e408 System.Object
  114 000000000579b620            1         1 0000000011bb93c0  1884 304   00000001bf974a90 System.Object
  124 0000000005a44d48            1         1 000000000e7a6170  2300 272   000000019f853fe8 System.Object
  146 0000000005a44688           99         1 000000000588cbf0  13e0  38   000000017f71c4f8 System.Object
  155 0000000005a44f88            1         1 0000000011bba530  2274 301   000000019f82f120 System.Object
  157 0000000005a45018            1         1 0000000011bbf0c0  2034 290   000000015f952980 System.Object

Can anyone explain the “99” in column “MonitorHeld”?

Has anyone a a link to a complete reference documentation of this command?

Thanks,
Alex

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1 Answer

  1. Editorial Team

    The MonitorHeld refers to how many monitors are held by that specific SyncBlk.

    Each time you have contention on a lock, you’ll have 1 owner held syncblk. Each waiter on a lock holds 2.

    Your 99 means that you have one object "owning" the lock, and 49 objects waiting on the lock (49×2 + 1 = 99).

    The best discussion and detailed explanation of !syncblk I’ve found is this one by Tess Ferrandez.

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