[Python-ideas] async: feedback on EventLoop API

[Jasper St. Pierre]

A lot of things become trivially easy if they assumption is that they can
never fail.

Deferreds/Promises/Tasks/Futures are about sane error handling, not sane
success handling.

(There's a few parts in the current proposal where this falls short, like
par, but that's another post)


On Tue, Dec 18, 2012 at 10:44 PM, Shane Green <shane at umbrellacode.com>wrote:

> Ignoring the API overlap with Futures/Promises for a moment, let me throw
> out this straw man approach to the event loop that seems to my naive eye
> like it pull together a lot of these ideas…
>
> Rather than passing in your callbacks, factories, etc., asynchronous APIs
> return a lightweight object you register your callback with.  Unlike
> promises, deferrers, etc., this is a one-time thing: only one callback can
> register with it.  However, it can be chained.  The registered callback is
> invoked with the output of the operation when it completes.
>
> Timer.wait(20).then(callme, *args, **kw)
> # I could do
> Timer.wait(20).then(callme, *args, **kw).then(piped_from_callme)
>
> #I could not do
> handler = Timer.wait(20)
> handler.then(callme)
> handler.then(callme2) # this would throw an exception.
>
> # I/O example…
> sock.accept().then(handle_connection) # invokes handle_connection(conn,
> addr)
> # Read some data
> conn.read(1024).then(handle_incoming) # handle_incoming invoked with up to
> 1024 bytes, read asynchronously.
> # Write some data
> conn.write("data").then(handle_written) # handle_written invoked with up
> number 5, giving number of bytes written async.
> # Connect HTTP channel and add it to HTTP dispatcher.
> channel.connect((hostname,80)).then(dispatcher.add_channel)
>
>
> # Listen to FD's for I/O events
> descriptors.select(r, w, e).then(handle) # handle(readable, writables,
> oobs)
>
> It seems like only supporting a single callback per returned handle lets
> us circumvent a lot of the weight associated with normal
> promise/future/deferred pattern type implementations, but the chaining
> could come in handy as it may cover some of the use-cases being considered
> when multiple events per fd came up, plus chaining is pretty powerful,
> especially when it comes at little cost.  The API would be much more
> extensive than "then()", of course, with things like "every", etc. we'd
> have to pull examples from everything already discussed.  Just wanted to
> throw out there to get beat up about ;-)
>
>
>
> Shane Green
> www.umbrellacode.com
> 805-452-9666 | shane at umbrellacode.com
>
>
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>
>


-- 
  Jasper
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