WinSetFocus has a subtle bearing on message processing since it selects a new active thread and new current input receivers for system messages.

Note:

Focus may be changed by a third party.

These are the essential steps in WinSetFocus processing:

• WM_FOCUSCHANGE is sent to the message thread losing the focus.

• The current window in focus is changed.

  pwndfocus points to the WND of the focus owner.

• Unlock the system queue if locked.

  The MQ of the current system queue owner is pointed to by pmqsyslock. This is set to zero if it points to the MQ of the current focus owner.

• The target window's message thread is marked as the new focus owner.

  pmqfocus is set to the address of the new focus owner's MQ.

• The target thread's message queue is made the current mouse and keyboard input receiver.

  pmqMouseWake and pmqKeyWake are set to the address of the new focus owner's MQ.

• The new focus owner's message thread is marked as the new active thread.

• A priority boost is applied to the new focus owner's message thread.

• WM_FOCUSCHANGE is sent to the message thread gaining the focus.

This processing is illustrated in the following diagram:

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