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* System.Console.Regions handling of outputConcurrent and errorConcurrent
when the output lacks a newline is surprising. The output may never be
displayed. A better approach:
When output arrives that lacks a newline, allocate a region for it
and buffer it in that region, so it displays immediately and more
output will go to the same region. When a newline arrives, close the
region and scroll up the completed line the same way any completed region
is displayed.
* Parts of System.Console.Concurrent may not be async exception safe.
If a thread is running an action from that module and an async exception
is sent to it, it may result in a deadlock or other problem.
(System.Console.Regions has been made safe,
also outputConcurrent and errorConcurrent.)
Particularly problematic is takeOutputLock', which takes the lock
and then outputs buffers to the console. If the emitOutputBuffer
calls are interrupted by async exception, it will be left locked
and the buffered output is also lost. But masking them is not good
because emitOutputBuffer could run for a long time in some situations.
fgProcess and bgProcess also do stuff with registerOutputThread/unregisterOutputThread
that may not be async exception safe.
And createProcessForeground uses takeOutputLock but then calls fgProcess,
which could be interrupted (during its call to registerOutputThread)
before it starts the async thread that drops the lock.
One approach to all this might be to fork off a worker thread,
which will thus be immune to any async exception directed at the calling
thread.
* Calling setConsoleRegion with something that throws an error
will cause no further display updates to happen.
The exception in the thunk will crash the displayThread,
and that is not waited on until the action passed to displayConsoleRegions
finishes, so the exception is deferred to that point. Of course if the
action never finishes, that hides the exception.
It does seem this should be improved, by catching the crashing
displayThread and ideally propigating the exception immediately.
But displayConsoleRegions would need to use a different class than
the current MonadIO to be able to do that. Eg, MonadBaseControl
so lifted-async can be used, or a class that lets the action be
canceled.
Or it could be dealt with by having setConsoleRegion force the thunk
before passing it over to the displayThread. But the instance
ToRegionContent (STM Text) seems to prevent doing that.
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