ExAcquireRundownProtectionEx function

The ExAcquireRundownProtectionEx routine tries to acquire run-down protection on a shared object so the caller can safely access the object.


BOOLEAN ExAcquireRundownProtectionEx(
  ULONG           Count



A pointer to an EX_RUNDOWN_REF structure that was initialized by a previous call to the ExInitializeRundownProtection routine. The run-down protection routines use this structure to track the run-down status of the associated shared object. This structure is opaque to drivers.


The amount by which to increment to the run-down instance count of the object. The count is incremented only if the routine returns TRUE. For more information, see Remarks

Return value

ExAcquireRundownProtectionEx returns TRUE if the routine successfully acquires run-down protection for the caller. Otherwise, it returns FALSE. A return value of FALSE indicates that the run down of the object has started and that the object must be treated as invalid.


To safely access a shared object, a driver calls ExAcquireRundownProtectionEx to acquire run-down protection on the object.

The RunRef parameter points to an EX_RUNDOWN_REF structure that tracks the run-down status of the associated object. This status information includes a count of instances of run-down protection that are currently in effect on the object. The ExAcquireRundownProtectionEx and ExReleaseRundownProtectionEx routines increment and decrement this count by arbitrary amounts. Two related routines, ExAcquireRundownProtection and ExReleaseRundownProtection, increment and decrement this count by one.

As long as the run-down block itself is nonpaged, this function can be called at DISPATCH_LEVEL.

For more information, see Run-Down Protection.


Minimum supported client Available starting with Windows Server 2003.
Target Platform Universal
Header wdm.h (include Wdm.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe
IRQL <= DISPATCH_LEVEL (see Remarks)
DDI compliance rules HwStorPortProhibitedDDIs

See also