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From Gordon Sim <g...@redhat.com>
Subject Re: 'client' APIs again
Date Tue, 12 Aug 2014 10:08:14 GMT
On 08/12/2014 10:25 AM, Alan Conway wrote:
> On Mon, 2014-08-11 at 16:47 +0100, Gordon Sim wrote:
>> Thanks very much for the comments, Alan, some responses inline...
>> On 08/11/2014 03:01 PM, Alan Conway wrote:
>>> Naming: I hate things called *_tools, *_utils etc. We should find a more
>>> descriptive name. Not foo or fred or whatchymacallit or dingdong or
>>> doofer either. Ideally these classes might all just end up in the proton
>>> package, or maybe as a subpackage like proton.events or proton.reactor.
>> I personally think they should (generally) be kept distinct from the
>> current proton package to make it clear that they are additive and
>> optional. A subpackage would be ok, I just didn't want to mix this with
>> dependent edits to the proton tree itself to begin with. It may even be
>> that not all the additional pieces belong in the same package.
> Fair enough. I like the sub-package but it needs to be a little more
> descriptive than proton.utils. proton.reactor is growing on me a bit.
> proton.events is not so bad - it's all about handling a proton.Event
> after all.

Yes, 'proton events' is not bad.

I did want to convey the notion that these are various optional pieces 
of a 'toolkit' for making the core engine API easier to use rather than 
a fixed API in their own right.  That is perhaps a subtle (or 
meaningless?!) point, and may not be something to be conveyed in a 
package name... How do you feel about 'eventkit'?

I'll change to proton_events for now to see how that feels.

>>> Runtime is a bit vague as a name as well though I haven't got a better
>>> idea.
>> Yes, this was unpopular with other I spoke to also. I reverted to my
>> original name - Container - which isn't ideal either. Any suggestions
>> from other gratefully considered.
> Its funny how often we run into this problem in this business. "Object",
> "Entity", "Thing", "Class", "Type",
> "IHaveToCallItSomethingButIReallyDontWantToBeSpecific" :)
> Looking at the code, Runtime does nothing but add connect and accept to
> SelectLoop, and SelectLoop is basically an Event pump. I get that we
> need to allow other forms of event pump in future, e.g. EPollLoop or
> whatever.
> So I would first suggest changing the name to
>   EventLoop { connect(); accept(); run(); }

Yes, I toyed with that as well and I do agree it is a more descriptive 
name. I felt it was adding something to an event loop by tying things 
together such that the event loop was operating on sockets boiund to 
AMQP connections. However as you say perhaps its really just making it 
more 'fully functional'...

I'll go with EventLoop for now, it's better than anything else.

> Since this is really just a "fully functional" general event loop, based
> on some concrete type of event pump implementation (e.g. SelectLoop)
> class EventLoop:
>      def __init__self(self, handlers=None, PumpClass=SelectLoop):
>          self.handlers = handlers or [ default_handlers...]
>          self.loop = PumpClass(Events(ScopedDispatcher(), *handlers)
> Note that as it stands the current Runtime/SelectLoop contract is not
> really suitable for adding new types of pump since RunTime.connect knows
> about Selectables,

I _think_ selectables could be used with other types of loop also. The 
key is that they have a file descriptor associated with them, can be 
readable or writable and can read or write respectively when that is the 

> but that contract is something for integrators or
> advanced users adding new types of pump so lets get the general user
> interface right first.


> I did also consider flipping it and making EventLoop an abstract base
> for SelectLoop and future pumps, but I'm not sure that helps anything. I
> like a separate class that is the end user interface and entirely
> separate classes for implementation details.
> --- python tips (apologies if obvious these are things I only figured
> out recently)
> 1. don't use import *. E.g. use "from proton import Events,...."
> import * makes it easier to write but harder to read since you have to
> consult other files to figure out where things come from.

Yes, I'll change that.

> 2. NEVER use map/list literals as keyword argument defaults!
> def this_is_bad(handlers=[]): ....
> because the list/map is created at module load time NOT each time the
> function is called!!! Since lists & maps are mutable the default can
> easily be inadvertently changed . Very hard to debug!

Good point. I don't think I have anything like that at present but will 
avoid adding it.

>>> Messages and threads: once received an app will want to dispatch
>>> messages based on address and other properties and allocate processing
>>> to threads in various ways. This is (should be) orthogonal to the API
>>> you are designing here but we need to make sure we have adequate thread
>>> safety and don't create limitations in the API that make things
>>> difficult.
>> I agree that more thought and examples on how to interact with other
>> threads is important. However at the same time, I want to avoid trying
>> to make everything threadsafe.
> Agreed.
>>> E.g. the app may want to process messages from a single
>>> proton connection (i.e. a single event stream) in multiple threads and
>>> send reply messages back to the same connection from arbitrary threads.
>> The proton connection object is not threadsafe, and I don't think that
>> should change.
> Agreed. What I'm getting at is there's a need for more tools (thread
> pools, thread safe queues) to allow people to write multi-threaded
> message servers that aren't necessarily tied to the threading model of
> proton.

Yes, we are in complete agreement I think.

> But I think that should be an add-on not a change to what you
> are doing here, so probably a distraction at this point.

We shouldn't delay it too long though, I agree.

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