Implement level triggering for windows

[carllerche]

The windows selector uses a linked list of currently active level-triggered events. When an event arrives and the socket is registered with level-triggered, the event is tracked in this linked list. Every call to select events will include all elements in this list. When an operation is performed on the socket such that the socket is no longer ready, the event is removed from the linked list.

Closes #241

Remaining

• Move calls to unset_readiness into schedule_foo functions.
• Possibly combine Registration::deregister & deregister2
• Remove LinkedList
• UDP support
• Uncomment prior tests using level

[alexcrichton]

How come this ended up being exported? Shouldn't this be an internal implementation detail?

[carllerche]

Poll is a public API that provides polling on only sockets (no timer / notifications). It returns IoEvent. I'm confused how Mio compiled before without having this exported.

However, I will track this as part of the api discussion

[reem]

rustc's privacy tracking is not so thorough - if something is declared with pub rustc considers it public and allows it in exported signatures, it need not be actually exported at the crate level

[carllerche]

@alexcrichton I have made the changes you suggest. Look good? TCP support should be done, but I still have some more outstanding items (tracked in the PR description).

[alexcrichton]

I think this may want to be deferred until the actual mem::forget below. If the me.iocp.defer branch is taken the readiness should still be applicable.

[alexcrichton]

Oh wait scratch that, it looks like defer will end up calling push_event which ends up doing the right thing for level triggering, so this should be fine.

[alexcrichton]

👍

[carllerche]

Ok, this is not a candidate for merging (I will squash before merging)

cc/ @alexcrichton

[alexcrichton]

You could also do this match via or_insert(event) and then or-in the kind, it at least avoids the Entry import (but works either way)

[alexcrichton]

I think there may also want to be some writable level handling for UdpSocket, but otherwise lgtm r+