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KeRevertToUserAffinityThreadEx routine

The KeRevertToUserAffinityThreadEx routine restores the previous affinity of the current thread.

Syntax


VOID KeRevertToUserAffinityThreadEx(
  _In_  KAFFINITY Affinity
);

Parameters

Affinity [in]

A KAFFINITY-typed variable that specifies the new system affinity of the current thread. Set this parameter to the value that was returned by a previous call to the KeSetSystemAffinityThreadEx routine.

Return value

None

Remarks

KeRevertToUserAffinityThreadEx changes the affinity of the current thread. The affinity value is a mask that identifies a set of processors on which the thread can run. If successful, the routine schedules the thread to run on a processor in this set.

If the Affinity value is nonzero, KeRevertToUserAffinityThreadEx sets the affinity mask of the thread to the Affinity value. If the Affinity value is zero, KeRevertToUserAffinityThreadEx restores the original user affinity mask of the thread. This original user affinity mask was saved in the thread object by a previous call to KeSetSystemAffinityThreadEx. A call to KeRevertToUserAffinityThreadEx has no effect unless it is preceded by a call to KeSetSystemAffinityThreadEx.

If the Affinity value is nonzero, the routine changes the affinity mask of the current thread to the Affinity value only if both of the following are true:

  • The Affinity value is valid (that is, only mask bits that correspond to logical processors are set).

  • At least one of the processors that is specified in the Affinity value is active.

If either of these conditions is not met, the call to KeRevertToUserAffinityThreadEx has no effect.

Windows 7 and later versions of Windows support processor groups. Drivers that are designed to handle information about processor groups should use the KeRevertToUserGroupAffinityThread routine, which specifies a processor group, instead of KeRevertToUserAffinityThreadEx, which does not. However, the implementation of KeRevertToUserAffinityThreadEx in Windows 7 and later versions of Windows provides compatibility for drivers that were written for earlier versions of Windows, which do not support processor groups. In this implementation, a nonzero Affinity value is an affinity mask that specifies a set of logical processors in group 0 on which the thread can run. If Affinity is zero, the thread reverts to its original user-mode group number and affinity mask.

If KeRevertToUserAffinityThreadEx is called at IRQL <= APC_LEVEL and the call is successful, the new (reverted) affinity mask takes effect immediately. When the call returns, the calling thread is already running on a processor that is specified in the new affinity mask. If KeRevertToUserAffinityThreadEx is called at IRQL = DISPATCH_LEVEL and the call is successful, the pending processor change is deferred until the caller lowers the IRQL below DISPATCH_LEVEL.

Requirements

Version

Available in Windows Vista and later versions of Windows.

Header

Wdm.h (include Wdm.h, Ntddk.h, or Ntifs.h)

Library

Ntoskrnl.lib

IRQL

<= DISPATCH_LEVEL (see Remarks section).

DDI compliance rules

PowerIrpDDis, HwStorPortProhibitedDDIs

See also

KAFFINITY
KeRevertToUserGroupAffinityThread
KeSetSystemAffinityThreadEx

 

 

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