I wrote:
> I was wondering where to trigger SafeState. I first thought it would be
> sufficient to do this higher up, where we are going to wait for the user
> to type a character and nothing is pending. Then it's safe to deal with
> any callbacks.
>
> However, think of this scenario:
> 1. In a safe state, SafeState is triggered.
> 2. Waiting for a character, receive a message.
> 3. Invoke callback for the message, it uses ch_evalexpr().
> 4. While in ch_evalexpr() another message arrives. Since it's
> not safe now, work is postponed.
> 5. ch_evalexpr() finishes
> 6. go back to waiting for a character
>
> Now, so long as the user doesn't type anything, the work won't be
> executed. That may take long time. Or the user is actually waiting for
> the work to be done, which is a kind of deadlock.
>
> Thus it seems that we need to trigger SafeState also before 6. Under
> the condition we started waiting for a character in a safe state.
> And it was not safe at some moment (to avoid it being triggered too
> often).
>
> It does mean that the display won't be updated, thus we would need to do
> that, like when a timer callback was invoked.
>
> Does this sound OK?
I decided to give it a go and did an implementation of SafeState.
It triggers in Normal, Insert and Command-line mode when nothing is
pending. And when a blocking channel call has been made, where the
state was safe before blocking, so that when something is postponed it
can be handled afterwards.
It may be that we need to check more conditions whether it is actually
"safe". And some things depend on what the requirements for "safe" are.
E.g. currently it is not checking for Visual mode, you can use mode()
for that. And it doesn't check whether the screen is scrolled (not sure
how you would check for that, might need the state() function).
When SafeState is triggered after the blocking channel call, we are in
the input loop, thus no screen update will take place. You can use
:redraw, but in Command-line mode that might not work well.
Anyway, please try it out, so we can decide whether we can keep
SafeState, modify it, or perhaps drop it.
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