[Octave-bug-tracker] [bug #56143] gui hangs on osx when switching between windows

[argus]

Follow-up Comment #15, bug #56143 (project octave):

I built a diagnosis tool leveraging ktrace facility in Mac. The tool reports
the main thread is waiting to write to ptmx after hundreds of successful
writes. The parameters to all the write system call are identical(fd ->
/dev/ptmx, same cbuf and nbytes = 3). 

By comparison, it reports the difference on the main thread and QThread
between the normal execution and the hang. Normally the main thread will be
woken up by the QThread, and therefore the write syscall returns success.
However, when the spinning beachball appears, the wakeup is missing.

On the Qthread side, it emits wakeup after pselect and read in normal
execution. Right before the hang, it starts writing to /dev/ttys00X, and is
blocked after hundreds of successful writes(parameters are identical too).

I suspect if there is a deadlock between the two threads and hope the
information could provide some hints.

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