Cliff Jansen commented on PROTON-640:

from https://reviews.apache.org/r/24159

This patch follows the QPID AsynchIO.cpp version fairly closely with the 
following main differences:

- addition of async connect
- multiple outstanding concurrent writes (a write pipeline)
- non-buffered reads
- graceful close progressing to hard close (much as proposed in QPID-5668)

Careful scrutiny of the selector API change is warranted (constructor).

Thread safety is currently assured only by isolating a paired pn_selector_t and 
pn_io_t from other such pairs. If anticipated use cases suggest either that 
multiple selectors be used with an io, or with multiple io's, or that a socket 
should be movable between selectors during it's lifetime, then additional 
locking semantics will be required. These scenarios come for free in Linux 
where the OS barrier takes care of concurrency issues. By contrast, the Windows 
code implements the selector in user space.

This API change just forces the pairing of the selector with the io. The user 
is still expected to free the selector when done. Perhaps this should be 
handled by the io when it closes, or some alternative API mechanism should be 
used. In any event, if the supported use cases preclude closely linking one 
selector with one io, then this is moot.

Performance notes. The use of a write pipeline has a significant effect on 
sending performance, especially with a small number of connections. It would 
probably be a useful enhancement for the QPID code. On the read side, no async 
read buffer is used (relying instead on the OS input buffering system). This is 
because pn_recv() copies out the bytes anyway (rather than passing a buffer as 
in QPID).

> IO completion port Windows IO for Proton
> ----------------------------------------
>                 Key: PROTON-640
>                 URL: https://issues.apache.org/jira/browse/PROTON-640
>             Project: Qpid Proton
>          Issue Type: Improvement
>          Components: proton-c
>    Affects Versions: 0.7
>         Environment: Windows
>            Reporter: Cliff Jansen
>            Assignee: Cliff Jansen
>             Fix For: 0.8
> Provide a native IO completion port layer similar to the C++ QPID version for 
> Proton.

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