[SSSD] Design question

Simo Sorce ssorce at redhat.com
Fri Oct 16 13:19:38 UTC 2009


On Thu, 2009-10-15 at 17:26 -0400, Dmitri Pal wrote:
> Hi,
> 
> Couple questions about async processing.
> The communication usually consists of several parts. Imagine that you
> have an object that is responsible for some sort of communication
> (socket, pipe, file, bus - whatever).
> Here are the basic things that can happen with such object:
> * Object is created
> * Communication channel is opened
> * Message is sent (and may be you get response back)
> * Communication channel is closed
> * Object is destructed
> 
> Object creation and destruction are the same regardless of whether the
> communication is synchronous or asynchronous.
> They are pretty straightforward. So let us talk about the other three.
> Definitely communication on the channel can (and should) be asynchronous
> - this is the whole purpose.
> But what about opening the channel. Should a file or socket be always
> opened as "O_NONBLOCK" or
> the event library would set the flag on the FD itself?
> I guess the question who is responsible for making socket/fd nonblocking
> the creator of it or the async library that provided the event loop?

Usually whoever opens the channel is responsible for setting O_NONBLOCK,
but this seem more convention than a hard rule.
You can decide to check if O_NONBLOCK is set or not and refuse to
operate asynchronusly returning errors if it is not I guess.

> Now imagine the situation: the opening of the channel includes actually
> two steps, establishing the channel itself (TCP for example) and sending
> some sort of the HELLO message.
> Can this hello message be done synchronously or the  connection should
> be established in async way and the hello message should be treated as
> any other message?
> I understand that the preferred way is to do it asynchronously but the
> question is: is it acceptable not to at least in the first implementation?

This is your call :-)
But Sumit seem to have described a good way to do it otherwise.

> Same question about closing the channel when this operation involves
> sending some sort of good bye message first. Is it acceptable to send
> and close in one step synchronously or not?

As above.

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York




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