Putting aside conversations, let's discuss another example: property
injection.
Suppose the user's business logic modifies a stateless instance's injected
property.
@Property
protected String currency; // configured via SCDL and injected by container
myMethod() {
....
currency = "blah";
}
So Dave, I take it you're arguing that, if the container were to pool
stateless instances, it would be responsible for ensuring that in later
dispatches of this same instance, the 'currency' property would appear as if
it were freshly-injected upon the business logic reading its value.
This capability strikes me to be of so little value to the app programmer
that I think the ideal situation would be for the spec to disallow this in
the stateless programming model and to say that the injected data is
read-only.
I don't see how this is a common sense issue either. This is a new
programming model, with a new choice to be made. Going back to EJB again,
we see a model where one had to understand the difference between instance
creation and going in and out of the ready pool between dispatches. Maybe
you're saying this is obviously undesirably complex, but on the flip side
here is a component model that was widely used which employed these
concepts. So I don't see it as too complicated to say, "it's stateless, so
you don't own the instance, so don't mess with the injected instance
variables."
Scott
On Mon, Oct 13, 2008 at 4:01 PM, scabooz <[EMAIL PROTECTED]> wrote:
> Hi guys,
>
> I'm having a hard time following this latest branch in the discussion, but
> I think there is a basic principle that needs to be asserted, which is that
> instance pooling must be unobservable to the business logic. This is just
> common sense, and anything else will make the programming model more
> difficult to understand. More specifically, when the runtime hands an
> instance to the business logic, the state of that instance should be
> identical regardless of whether the container new-ed up the instance or
> obtained it from a pool.
>
> Someone is going to jump on the "where does it say that in the spec?"
> question. It's probably not explicit, but it should be, and there are open
> issues in the OASIS work to clarify and lock it down. All I can say to this
> question is that the above is the spec intention, and is a principle that
> will cause the least surprise and most success for users.
>
>
> Dave
>
> ----- Original Message -----
> *From:* Scott Kurz <[EMAIL PROTECTED]>
> *To:* [email protected]
> *Sent:* Friday, October 10, 2008 4:16 PM
> *Subject:* Re: [jira] Created: (TUSCANY-2635) Pool stateless-scoped Java
> impl instances
>
> Simon,
>
> Sorry my line of reasoning didn't come through so well.
>
> I was actually trying to argue the point that a new conversation should NOT
> be started just because a stateless instance is obtained from a pool.
>
> However, I was trying to address the opposite point of view (a new
> conversation should be started), which I think is where you were coming
> from.
>
> If the specs had said something like "at the beginning of a scope,
> references are injected", then we'd have an answer (opposite to my
> reading). If you take Java C&I lines 193-195 to mean the same, we'd also
> contradict my interpretation.
>
> In contrast, I'm taking the lack of clarity as a signal that this is up to
> the runtime implementation to work out So the net is (per my reading),
> that you can not assume a new conversation per stateless dispatch, if you're
> relying on reference injection to start the conversation....and you have to
> use programmatic means if you want this.
>
> Scott
>
>
>
>
>
>
> On Fri, Oct 10, 2008 at 12:18 PM, Simon Laws <[EMAIL PROTECTED]>wrote:
>
>>
>>
>> On Fri, Oct 10, 2008 at 4:49 PM, Scott Kurz <[EMAIL PROTECTED]> wrote:
>>
>>> OK, So
>>>
>>> On Fri, Oct 10, 2008 at 10:08 AM, Simon Laws <[EMAIL PROTECTED]>wrote:
>>>
>>>>
>>>> Hi Scott
>>>>
>>>> Can you say a little more about what the implications for pooling
>>>> stateless instances would be, for example,
>>>>
>>>> 1st call - Create object
>>>> @Reference injected
>>>> @Init run
>>>>
>>>> 1st Operation execution ends
>>>> @Destory called
>>>> Reset any conversational/callback state help in the components
>>>> references
>>>> object put in pool
>>>>
>>>> 2nd call - Retrieve object from pool
>>>> @Init called
>>>>
>>>> 2nd Operation execution ends
>>>> @Destory called
>>>> Reset any conversational/callback state help in the components
>>>> references
>>>> object put in pool
>>>>
>>>> Is that the sort of thing you were thinking of in order to remove the
>>>> injection overhead?
>>>>
>>>>
>>> Simon, yes, unlike, say ejbCreate() for a SLSB, the @Init is supposed to
>>> get called every time for a stateless invocation
>>>
>>> So let's look at conversational state, which is the type of concern I was
>>> hoping to get to. I'm pretty ignorant of what this looks like at a low
>>> level. At a high level, though, a new conversation is supposed to begin
>>> every time a conversational-interfaced-reference is injected into the client
>>> component.
>>>
>>> So, my naive take on this would be that this isn't all that useful when
>>> the client component is stateless, since you don't know when the container
>>> is going to give you a new stateless instance (with an
>>> already-started-conversation) or an existing one.
>>>
>>> So if you need better control over starting a conversation from a
>>> stateless component, you need to get your conversational reference
>>> programmatically.
>>>
>>> I suppose you could read into the specs the idea that they intended the
>>> references to be injected at the start of the scope..... there is this
>>> (which I don't believe helps):
>>>
>>> Java C&I - 1.2.2.1
>>>
>>> 192 If @Reference marks a public or protected field, the SCA runtime is
>>> required to provide the appropriate
>>> 193 implementation of the service reference contract as specified by the
>>> field type. This must done by setting
>>> 194 the field on an implementation instance. When injection occurs is
>>> defined by the scope of the
>>> 195 implementation.
>>>
>>> I don't think it helps since I don't see that the specs define this with
>>> respect to the Java impl scopes.
>>>
>>> So... given that my model is, we don't really consider this is a smart
>>> use case and we leave the conversation dangling in such a case... do we
>>> still have anything to worry about for conversations?
>>>
>>> Scott
>>>
>>
>> Hi
>>
>> If you did read into the specs that injection was intended to happen at
>> the start of each scope, i.e. in this case when an object is retrieved from
>> the pool, wouldn't that kill the performance improvement you are looking to
>> achieve?
>>
>> Not sure I understand the last sentence.
>>
>> So... given that my model is, we don't really consider this is a smart use
>> case and we leave the conversation dangling in such a case... do we still
>> have anything to worry about for conversations?
>>
>> If you don't clean up the conversation object then when you call through
>> the reference of a previously pooled component instance you will likely be
>> continuing a conversation that is already started. There is state referenced
>> behind the reference proxy and also in the conversation manager about onging
>> conversations. This state is removed when a component instance is removed
>> and we'd have to work out how to do the same if we were to pool stateful
>> instances. This is of course in the case where the business logic doesn't
>> end the conversation properly itself.
>>
>> Simon
>>
>>
>
