On Mon, Jan 28, 2013 at 2:48 PM, Saúl Ibarra Corretgé <saghul@gmail.com> wrote:
Hi all!
I haven't been able to keep up with all the tulip development on the mailing list (hopefully I will now!) so please excuse me if something I mention has already been discussed.
Me neither! :-) Libuv has been brought up before, though I haven't looked at it in detail. I think you're bringing up good stuff.
For those who may not know it, libuv is the platform layer library for nodejs, which implements a uniform interface on top of epoll, kqueue, event ports and iocp. I wrote Python bindings [1] for it a while ago, and I was very excited to see Tulip, so I thought I'd give this a try.
Great to hear!
Here [2] is the source code, along with some notes I took during the implementation.
Hm... I see you just copied all of tulip and then hacked on it for a while. :-) I wonder if you could refactor things so that an app would be able to dynamically choose between tulip's and rose's event loop using tulip's EventLoopPolicy machinery? The app could just instantiate tulip.unix_eventloop._UnixEventLoop() (yes, this should really be renamed!) or rose.uv.EventLoop, but all its imports should come from tulip. Also, there's a refactoring of the event loop classes underway in tulip's iocp branch -- this adds IOCP support on Windows.
I know that the idea is not to re-implement the PEP itself but for people to create different EventLoop implementations. On rose I bundled tulip just to make a single package I could play with easily, once tulip makes it to the stdlib only the EventLoop will remain.
It will be a long time before tulip makes it into the stdlib -- but for easy experimentation it should be possible for apps to choose between tulip and rose without having to change all their tulip imports to rose imports.
Here are some thoughts (in no particular order):
- add_connector / remove_connector seem to be related to Windows, but being exposed like that feels a bit like leaking an implementation detail. I guess there was no way around it.
They would only be needed if we ever were to support WSAPoll() on Windows, but I'm pretty much decided against that (need to check with Richard Oudkerk once more). Then we can kill add_connector and remove_connector.
- libuv implements a type of handle (Poll) which provides level-triggered file descriptor polling which also works on Windows, while being highly performant. It uses something called AFD Polling apparently, which is only available on Windows >= Vista, and a select thread on XP. I'm no Windows expert, but thanks to this the API is consistent across all platforms, which is nice. mAybe it's worth investigating? [3]
Again that's probably for Richard to look into. I have no idea how it relates to IOCP.
- The transport abstraction seems quite tight to socket objects.
I'm confused to hear you say this, since the APIs for transports and protocols are one of the few places of PEP 3156 where sockets are *not* explicitly mentioned. (Though they are used in the implementations, but I am envisioning alternate implementations that don't use sockets.)
pyuv provides a TCP and UDP handles, which provide a completion-style API and use a better approach than Poll handles.
So it implements TCP and UDP without socket objects? I actually like this, because it validates my decision to keep socket objects out of the transport/protocol APIs. (Note that PEP 3156 and Tulip currently don't support UDP; it will require a somewhat different API between transports and protocols.)
They should give better performance since EINTR in handled internally and there are less roundtrips between Python-land and C-land.
Why would EINTR handling be important? That should occur almost never. Or did you mean EAGAIN?
Was it ever considered to provide some sort of abstraction so that transports can be used on top of something other than regular sockets? For example I see no way to get the remote party from the transport, without checking the underlying socket.
This we are considering in another thread -- there are in fact two proposals on the table, one to add transport methods get_name() and get_peer(), which should return (host, port) pairs if possible, or None if the transport is not talking to an IP connection (or there are too many layers in between to dig out that information). The other proposal is a more generic API to get info out of the transport, e.g. get_extra_info("name") and get_extra_info("peer"), which can be more easily extended (without changing the PEP) to support other things, e.g. certificate info if the transport implements SSL.
Thanks for reading this far and keep up the good work.
Thanks for looking at this and reimplementing PEP 3156 on top of libuv! This is exactly the kind of thing I am hoping for.
Regards,
[1]: https://github.com/saghul/pyuv [2]: https://github.com/saghul/rose [3]: https://github.com/joyent/libuv/blob/master/src/win/poll.c
-- Saúl Ibarra Corretgé http://saghul.net/blog | http://about.me/saghul
-- --Guido van Rossum (python.org/~guido)