On Fri, Nov 12 2021, Lars Ingebrigtsen wrote:

>> However, I would like to propose
>> that, in status_notify, the sentinel function should be called before
>> closing the file descriptors.  That way, the sentinel can read the
>> buffered output as suggested in the example.
>
> A sentinel usually doesn't read anything...

The idea is that the sentinel does something like this:

  (lambda (p _)
    (set-process-filter p filter)
    (while (accept-process-output p 0)))

First, it changes the filter from t to an actual function.  Then it
calls accept-process-output.  This in turn polls the file descriptors
and calls the filter function if there is buffered output.  If there is
no buffered output to read, then accept-process-output returns nil and
the while loop terminates.

All this happens after the process has terminated.  Granted, not a
particularly intuitive API.

However, the required change would be rather small, I think.  The patch
below shows how this could be done.  It basically moves the part that
closes the file descriptors after the call to exec_sentinel.