Hi Cliff,

comments inline

On 11. 09. 14 09:32, Cliff Jansen (JIRA) wrote:
> Proton is designed to provide an efficient IO layer that functions without 
> imposing a threading model on the application.  Applications may (1) roll 
> their own IO and just use the Proton engine, (2) use all Proton primitives, 
> (3) use some Proton primitives augmented by an external event loop.
> Case (1) is unrelated to this JIRA.  The others may be restated:
> Scenario 2: Proton event loop: a proton selector manages socket events for 
> all sockets placed in the selector, all associated sockets use pn_io_xxx() 
> calls.  Sockets outside the selector are "unmanaged" and passed through to 
> the OS socket function unchanged.
> Scenario 3: Third party event loop (no proton selector involved), all sockets 
> are treated as for "unmanaged" in scenario 2.

yay, looks like my use-case :)

> Scenario 4, 5...: Others to support?
> The problem:
> The Proton Posix pattern for efficient IO is:
>   "tell me when your (OS) buffer is ready for io transfer (in or out)"
> Whereas the normal Windows pattern is somewhat reversed (IO completion ports):
>   "tell me when you are done transferring data (to or from) my (user space) 
> buffer"
> The current Windows IOCP implementation (PROTON-640) tries to make the latter 
> look like the former with some constraints.   There should be documentation 
> specifying reasonable limits on Proton usage that may be falsely implied by 
> the API but do not translate efficiently to Windows.  Assuming that future 
> Windows implementations may adopt more aggressive performance strategies 
> (especially on the read side), I would propose something along the lines of:
>   a socket may only ever be used with a single pn_io_t in its lifetime
>     exception: a socket from pn_accept() is not yet associated with any 
> pn_io_t and its first use can be with any pn_io_t (or never with a pn_io_t at 
> all)

I'm not sure if it's implied, but pn_connect() and pn_listen() also need
to support 'third party event loop'.
Specifically, pn_connect() has to remain non-blocking (we get to know
about the connect error later in the external event loop)

>   send/recv/close may not be intermixed with similar non-Proton OS calls 
> (otherwise: out of order or lost data)
>   a socket can move once from an external loop to a proton loop, but never 
> the other way
>   pn_pipe() values can only be used with pn_read and pn_write and 
> pn_selector_select, they cannot participate in an external event loop.

External event loops should have their own mechanism how to signal
non-socket events into the loop.

>   Furthermore, there is no thread safety except:
>     threads may do concurrent pn_io_xxx() calls as long as no two are 
> simultaneous on the same socket (where xxx is send/recv/read/write)

This will break pn_io_error() and pn_io_wouldblock() as they are defined

>     pn_selector_select() is thread safe against 
> pn_read/pn_write/pn_send/pn_recv, but the outcome of the select is 
> indeterminate.  pn_selector_select() must be interrupted and restarted at any 
> time when other simultaneous IO may affect the outcome.

When you say 'interrupted' is there a simpler way than a pn_write() to
writeable pn_socket_t of pn_pipe()
 that has it's readable pn_socket_t associated with a pn_selectable_t
that is added to said pn_selector_t ? ;)

I have a feeling you don't really want/need to expose the pn_pipe(), but
add a
pn_selector_interrupt() and a mechanism of querying that for the caller
of pn_selector_select()
especially as you want to implement it completely differently on windows.

>     calls on different pn_io_t objects do not interact and are thread safe.
> If it is desirable for a socket to be used in an external loop after being 
> used in a Proton loop, we would need some sort of blocking calls along the 
> lines of:
>   pn_io_flush()
>   pn_io_drain()
> which would be no-ops on Posix but would unwind outstanding completions on 
> Windows.

this part sounds ok, if it is needed


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