warp the mouse to the primary screen. entering the primary
screen causes the primary screen's window to be hidden. the
deadlock occurs because hiding the window seems to post a
message then wait for it to be handled (or possibly it won't
send a message while a posted message is being handled).
thread A locks the mutex, warps the mouse, the hides the window.
thread B begins processing the mouse warp then tries to lock
the mutex. thread A is waiting on the event loop owned by B
while B is waiting on the mutex owned by A. this fix simply
hides the window asynchronously. however, there may be other
ways to cause a similar deadlock that have not been found.
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