LockCount

Interpreting Critical Section Fields in Windows Server 2003 SP1 and Later

 

In Microsoft Windows Server 2003 Service Pack 1 and later versions of Windows, the LockCount field is parsed as follows:

 

The lowest bit shows the lock status. If this bit is 0, the critical section is locked; if it is 1, the critical section is not locked.

The next bit shows whether a thread has been woken for this lock. If this bit is 0, then a thread has been woken for this lock; if it is 1, no thread has been woken.

The remaining bits are the ones-complement of the number of threads waiting for the lock.

 

As an example, suppose the LockCount is -22. The lowest bit can be determined in this way:

 

0:009> ? 0x1 & (-0n22)

uate expression: 0 = 00000000

 

The next-lowest bit can be determined in this way:

 

0:009> ? (0x2 & (-0n22)) >> 1

uate expression: 1 = 00000001

 

The ones-complement of the remaining bits can be determined in this way:

 

0:009> ? ((-1) - (-0n22)) >> 2

uate expression: 5 = 00000005

 

In this example, the first bit is 0 and therefore the critical section is locked. The second bit is 1, and so no thread has been woken for this lock. The complement of the remaining bits is 5, and so there are five threads waiting for this lock.