On Tuesday, September 3, 2013 9:04:40 AM UTC-7, Ben Fritz wrote:
> On Sunday, September 1, 2013 8:42:25 PM UTC-5, Geoff Greer wrote:
> > This patch adds asynchronous functions to vimscript. If you want to perform
> > an action in 700ms, simply:
> >
> > let timeout_id = settimeout(700, 'echo("hello")')
> >
> > To cancel the timeout before it's fired:
> >
> > canceltimeout(timeout_id)
> >
> > setinterval() also returns an id that can be used with canceltimeout.
> >
> > The reason for this patch is simple: asynchronous functionality is needed
> > to implement real-time collaborative editing in Vim. This is one of the
> > most voted-for features (see http://www.vim.org/sponsor/vote_results.php).
> >
> > Along with Matt Kaniaris, I founded Floobits to build real-time
> > collaboration into every editor. We wrote a plugin for Vim, but we had to
> > use hacks to get async behavior (abusing feedkeys or client-server). These
> > methods had side-effects such as breaking leaderkeys or other shortcuts.
> > After a lot of experimenting, we decided to try patching Vim.
> >
> > Since Vim is character-driven, we had to munge some low-level input
> > functions to get the desired behavior. We changed gui_wait_for_chars() and
> > mch_inchar() so that call_timeouts() is run every ticktime milliseconds.
> > The default ticktime is 100ms.
> >
> > This patch isn't finished yet, but it works on unix-based OSes. If the
> > reaction is positive, our intention is to change mch_inchar() (or something
> > similar) in other OS-specific files. That will get async functions working
> > for everyone.
> >
> > Even if our patch isn't the best approach, we'd love to help get async
> > functions in Vim. Doing so will open the door to a lot of cool plugins.
> >
> > Oh, and this is the first time either myself or Matt have submitted a patch
> > to Vim, so please be gentle.
> >
> > Sincerely,
> >
> > Geoff Greer
>
> Forgive me if I'm wrong, I didn't spend more than a few minutes looking over
> the patch.
>
> It looks like this is not really "asynchronous" behavior, but rather adding a
> timer-like hook into the main loop. Pro: no worries about thread safety, race
> conditions, etc. Con: if the function called by the timer event takes a long
> time, Vim hangs until it's done.
>
> If I'm correct, and this gets included, the help will need to be very
> explicit about making sure to limit the time taken by the function called!
> And there should definitely be a way to interrupt the action.
Ben,
You are correct in that we added a timer to the main loop. Looking over the
code once again, I think we should have altered the calls to select/poll
instead, but lets discuss the practical effect of this patch since we can work
out the details some time later.
Async does not imply parallelism nor safety- it only provides the illusion of
concurrency. Idle cpu time spent waiting is instead used to perform some other
task. Async frameworks make no such guarantee that every call not block the
event loop; it is incumbent upon the programmer to ensure that the event loop
is not blocked indefinitely. This is the definition and standard interface of
async programming for every popular framework I can think of that lives in a
scripting language- JavaScript, nodejs, twisted, event machine, and luvit.
The current alternative in Vim is to block forever, or worse yet, not write
useful software because it is impossible to do so as a Vim plugin. With a
proper settimeout, plugins have the option of returning control to the main
loop and checking in latter. I'd suggest a settimeout on the settimeouts is
not needed; plugins which cause too much trouble will either be fixed or
uninstalled.
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