[Python-ideas] The async API of the future

Richard Oudkerk shibturn at gmail.com
Sat Oct 20 12:56:41 CEST 2012

On 20/10/2012 1:33am, Greg Ewing wrote:
> That's been bothering me, too. It seems like an interface
> accommodating the completion-based style will have to be
> *extremely* fat.
> That's not just a burden for anyone implementing the
> interface, it's a problem for any library wanting to *wrap*
> it as well.
> For example, to maintain separation between the async
> layer and the generator layer, we will probably want to
> have an AsyncSocket object in the async layer, and a
> separate GeneratorSocket in the generator layer that wraps
> an AsyncSocket.
> If the AsyncSocket needs to provide methods for all the
> possible I/O operations that one might want to perform on
> a socket, then GeneratorSocket needs to provide its own
> versions of all those methods as well.
> Multiply that by the number of different kinds of I/O
> objects (files, sockets, message queues, etc. -- there
> seem to be quite a lot of them on Windows) and that's
> a *lot* of stuff to be wrapped.

I don't see why a completion api needs to create wrappers for sockets.  See


for an implementation of a completion api implemented for Unix (plus a 
stupid reactor class and some example server/client code).

The AsyncIO class is independent of reactors, futures etc.  The methods 
for starting an operation are

     recv(key, sock, nbytes, flags=0)
     send(key, sock, buf, flags=0)
     accept(key, sock)
     connect(key, sock, address)

The "key" argument is used as an identifier for the operation.  You wait 
for something to complete using


which returns a list of tuples of the form "(key, success, value)" 
representing completed operations.  "key" is the identifier used when 
starting the operation, "success" is a boolean indicating whether an 
error occurred, and "value" is the return/exception value.  To check 
whether there are any outstanding operations, use


(To make the AsyncIO class usable without a reactor one should probably 
implement a "filtered" wait so that you can restrict the keys you want 
to wait for.)


More information about the Python-ideas mailing list