On 9/4/07, Simon Laws <[EMAIL PROTECTED] > wrote:
>
>
>
> On 8/31/07, Simon Laws < [EMAIL PROTECTED]> wrote:
> >
> >
> >
> > On 8/31/07, Raymond Feng < [EMAIL PROTECTED]> wrote:
> > >
> > > In the same JVM, we now use a singleton object to keep all the
> > > metadata for
> > > the deployable composites running on the node. This has been proven to
> > > be
> > > problematic, especially in the case of Tomcat or Geronimo integration
> > > where
> > > applications are running in isolated address spaces. The partition is
> > > the
> > > portion of SCA domain visible to a given address space and its
> > > lifecycle is
> > > the same as an Web/JEE application (or some other modules).
> > >
> > > Then we have the following hierarchy:
> > >
> > > SCA domain (accross multiple nodes on the network)
> > > --- SCA node (I assume one node per JVM and one JVM per node)
> > > --- SCA partition (I assume one partition per address space in
> > > the
> > > JVM)
> > >
> > > Thanks,
> > > Raymond
> > >
> > > ----- Original Message -----
> > > From: "Simon Laws" < [EMAIL PROTECTED]>
> > > To: < [email protected]>
> > > Sent: Friday, August 31, 2007 9:46 AM
> > > Subject: Re: Rationalizing SCA Domain implementations
> > >
> > >
> > > > On 8/31/07, Raymond Feng < [EMAIL PROTECTED] > wrote:
> > > >>
> > > >> Hi,
> > > >>
> > > >> Comments inline.
> > > >>
> > > >> Thanks,
> > > >> Raymond
> > > >>
> > > >> ----- Original Message -----
> > > >> From: "Simon Laws" < [EMAIL PROTECTED]>
> > > >> To: "tuscany-dev" < [email protected]>
> > > >> Sent: Thursday, August 30, 2007 9:13 AM
> > > >> Subject: Rationalizing SCA Domain implementations
> > > >>
> > > >>
> > > >> > We now have a number of domain implementations in Tuscany Java
> > > SCA
> > > >> > including
> > > >> >
> > > >> > - The SCADomain interface
> > > >> > - DefaultSCADomain
> > > >> > - EmbeddedSCADomain
> > > >> > - HotUpdatableSCADomain
> > > >> > - DistributedDomain/Node
> > > >> >
> > > >> > Covering a number of scenarios
> > > >> >
> > > >> > - running a domain in a single node
> > > >> > - running a domain across multiple nodes
> > > >> > - Adding, removing, updating the contributions of a domain
> > > through the
> > > >> API
> > > >> > and automatically
> > > >> > - Activating/deactivating, starting/stopping deployable
> > > composites
> > > >> through
> > > >> > the API
> > > >> > - Starting, stopping components through the API
> > > >> > - Locating service in the domain through the API
> > > >> > etc.
> > > >> >
> > > >> > There are some scenarios that we don't cover at the moment
> > > >> >
> > > >> > - running multiple domains in a VM
> > > >>
> > > >> Why does one JVM want to join multiple SCA domains? IMHO, it might
> > > be
> > > >> over-engineered.
> > > >
> > > >
> > > > I think this depends on the answers to you second point.
> > > >
> > > >> What else?
> > > >> >
> > > >> > I would like to propose that we rationalize these various
> > > >> implementations
> > > >> > down to a more manageable number. I have a simple model in my
> > > mind of
> > > >> the
> > > >> > building blocks we have to deal with.
> > > >> >
> > > >> > 1/ The node.
> > > >> > Is responsible for running segregated domains in a VM
> > > >> > Associated with zero or more domains.
> > > >>
> > > >> I think we probably miss another layer here, the 'partition's in
> > > the same
> > > >> node. In a typical server hosting environment such as Tomcat or
> > > Geronimo,
> > > >> applications are isolated by address spaces (such as ClassLoader
> > > for java
> > > >> classes). The list of deployable composites coming from the same
> > > address
> > > >> space will form a partition. With this layer, we can better embed
> > > Tuscany
> > > >> to
> > > >> the various hosting environment and provide the flexibility for
> > > dynamic
> > > >> updates.
> > > >>
> > > >> With this in mind, the node will have an aggregate view of all the
> > > >> partitions within the node.
> > > >
> > > >
> > > > Can you say some more about what a "partition" is in the context of
> > > SCA?
> > > >
> > > > Asking the question in a different way, what is the implication of
> > > having
> > > > multiple "partitions" in the same domain? Is this like having
> > > separate
> > > > nodes
> > > > but with more efficient cross node comms mechaninsm, i.e. within the
> > > same
> > > > JVM?
> > > >
> > > >> 2/ The domain.
> > > >> > Logically knows about all of the artifacts of a domain.
> > > >> > Associated with one or more (in the distributed case) nodes.
> > > >> > A local representation of the domain (the SCADomain object)
> > > provides
> > > >> the
> > > >> > interface to wider domain
> > > >> >
> > > >> > There are some subtleties here about the timing of associating a
> > > domain
> > > >> > with
> > > >> > a node(s) but the simple case, which we implement at the moment,
> > > >> > is if you start a domain, start a node, associate the two
> > > together and
> > > >> > then
> > > >> > add contributions. The contributed components run on the node
> > > with
> > > >> > which
> > > >> > the local domain object is associated (more complex
> > > node/component
> > > >> > selection
> > > >> > algorithms can be imagined but we don't do this at present).
> > > >> >
> > > >> > Here are some suggestions based on the interfaces from the list
> > > of
> > > >> > existing
> > > >> > domain classes above, of the kind of things we need to be able to
> > > do;
> > > >> >
> > > >> > Domain
> > > >> > Create/destroy the domain based on its URI
> > > >> > Act of creating a domain object with a globally unique URI
> > > means
> > > >> > that
> > > >> > it
> > > >> > becomes part of that domain and can scope comonent invocations in
> > >
> > > >> > the context of that domain.
> > > >> > There should be a default hot update location if we want to
> > > maintain
> > > >> > that feature.
> > > >> > Contribution management
> > > >> > Add/remove contributions
> > > >> > Resulting composites/components sit ready to be started
> > > >> > Composite Management
> > > >> > Start/stop composite
> > > >> > Akin to adding a composite to the domain composite and
> > > activating
> > > >> it
> > > >> > Not sure how we identify a composite to be activated - by
> > > >> > composite
> > > >> > name? Currently it's done with a reference to the composite
> > > object
> > > >> > Do we need to expose separate activation operations?
> > > >> > Component Management
> > > >> > Start/stop component
> > > >> > Add.Remove listener
> > > >> > Not sure how the listener from the current interface is
> > > going to
> > > >> > be
> > > >> > used
> > > >> > getComponentInfo
> > > >> > There are some existng related component management interfaces
> > > here
> > > >> > also
> > > >> > LocateService
> > > >> > public abstract <B, R extends CallableReference<B>> R cast(B
> > >
> > > >> target)
> > > >> > public abstract <B> B getService(Class<B> businessInterface,
> > > >> > String
> > > >> > serviceName);
> > > >> > service name -> component name / service name
> > > >> > public abstract <B> ServiceReference<B>
> > > >> getServiceReference(Class<B>
> > > >> > businessInterface, String referenceName);
> > > >> >
> > > >> > We also need the domain to provide some systematic interfaces to
> > >
> > > >> support
> > > >> > distributed operation, for example,
> > > >> >
> > > >> > ServiceDiscovery
> > > >> > register/find service endpoint
> > > >> >
> > > >> > Node
> > > >> > Create/destroy the node based on its URI
> > > >> > Add/remove an association with a domain
> > > >> > start/stop a nodes activity
> > > >> >
> > > >> > Currently we have an approach, with the EmbeddedSCADomain, where
> > > the
> > > >> class
> > > >> > vends a series of management interfaces, contribution, model
> > > building
> > > >> etc.
> > > >> > for performing actions on the domain. This is useful as it allows
> > > >> > flexibility in how these management actions are implemented
> > > without
> > > >> > changing
> > > >> > all
> > > >> > of the domain implementation. It would also be appropriate, in
> > > the
> > > >> future,
> > > >> > to expose some of these interfaces as services to allow for
> > > remote
> > > >> > management of the
> > > >> > domain at a node.
> > > >> >
> > > >> > Would welcome thoughts about this generally. Also specifically do
> > > we
> > > >> need
> > > >> > to
> > > >> > maintain the detailed interfaces provided with EmbeddedSCADomain
> > > >> alongside
> > > >> > this.
> > > >> >
> > > >> > Regards
> > > >> >
> > > >> > Simon
> > > >> >
> > > >>
> > > >>
> > > >>
> > > ---------------------------------------------------------------------
> > > >> To unsubscribe, e-mail: [EMAIL PROTECTED]
> > > >> For additional commands, e-mail: [EMAIL PROTECTED]
> > > >>
> > > >>
> > > >
> > >
> > >
> > > ---------------------------------------------------------------------
> > > To unsubscribe, e-mail: [EMAIL PROTECTED]
> > > For additional commands, e-mail: [EMAIL PROTECTED]
> > >
> > > Hi Raymond
> >
> > I agree that the singleton is problematic.
> >
> > Can you explain what you mean by "address space" in the JVM. Is it the
> > namespace isolation afforded to classes by their class loader?
> >
> > Why would each "address space" not have a separate node? (of course this
> > depends on our definition of node :-)
> >
> > Maybe you could say a little about how you expect the classloader
> > hierarchy to work in Tuscany in this situation. I note that a number of
> > APIs take a class loader in Tuscany but I haven't spotted of any
> > samples/tests that demonstrate when this faility would be used.
> >
> > I will take a look at the Geronimo integration code to try and get a
> > better understanding of this in the morning.
> >
> > Simon
> >
> > Hi Raymond
>
> I spent yesterday morning running up the Geronimo implementation. I think
> I understand what you are saying now. It seems that as jars (containing
> composites) are deployed to Geronimo then in the current integration
> approach a new model resolver is created with a separate class loader and
> the jar is contributed to the single domain that Geronimo knows about (as
> defined by the plan). Will a Geronimo instance only ever know about a single
> domain?
>
> So I believe what you refer to as the partition is created by virtue of
> the separate class loader that is use to resolve the resource for each
> contribution.
>
> I'm trying to work this into the interfaces I have in mind but I've been
> round the houses a bit as I didn't think about this originally. I'll post
> some more thoughts shortly when I can joint the dots up.
>
> Simon
>
>From an implementation point of view I can enforce the restriction that one
node only deals with one domain. In the logical world the concept of a
domain spanning many runtime environments and of a physical compute engine
(JVM, process, cluster etc) supporting many domains leads to
Logical Domain n --- n Physical Compute Engine (could be JVM)
from a java implementation point of view, with this restriction, this
resolves to
Domain 1 --- 1 Node
Where Domain is the object representing a domain running on a node which is
able to find out about the other parts of the domain
and Node provides the runtime resources to this part of the domain. I still
contend that any number of Domain/Node pairs can be started within a JVM
Logical Domain 1 ---- n Domain 1 ---- 1 Node n --- n Physical Compute
Engine (could be JVM)
I think I understand what Raymond means by a partition of a node now. The
implication being that, in Java, a contribution is added to a domain with
information about not only what node it will run on but also what part of
that node. This information is currently a classpath which is used to
construct a resolver under the covers. Not sure if there is a more general
defintion of a partition key.
Domain 1 ---- 1 Node 1 --- n "Partition"
So I have changed the new domain representation as follows
A new domain implementation is based on the SCADomain interface without the
static creation methods
The node model is now internalized inside of this domain object.
It is effectively the really small runtime but with the addition of
being able to record contributions against partition keys.
The node can have a name with is used, as before, when the domain is
deployed on more than one node.
As per the first post, the Domain will vend out managers for Components,
Composites, Contributions
So if you want to create a stand alone domain, i.e a domain that relies on a
single node, as we do in many of our samples you can do.
myDomain= new DomainImpl("SomeDomainName");
myDomain.start();
myDomain.getContributionManager
("SomeContributionUrl").startContribution();
If you want to add a contribution into a partition you would do
myDomain.getContributionManager("SomeContributionUrl",
classLoader).startContribution();
In the previous case no node name was give so a default node is created for
you but it can't talk to anything else. If you want the domain to be part of
a collection of nodes you give the domain representation a node name
// Create the first domain node
domainNodeA = new DomainImpl("SomeDomainName", "nodeA");
domainNodeA.start();
domainNodeA.getContributionManager("nodeA/").startContribution();
// Create the second domain node
domainNodeB = new DomainImpl("SomeDomainName", "nodeB");
domainNodeB.start ();
domainNodeB.getContributionManager("nodeB/").startContribution();
The managers allow us to control the various aspects of the domain,
e.gcontributions, composites, components (I'm effectively using the
existing
component manager for the last bit). It gives us something to hang the hot
updateable behaviour from also but I haven't added that bit in yet.
I have code for this but it doesn't work quite yet. So any comments welcome.
Simon
[1] http://www.mail-archive.com/tuscany-dev%40ws.apache.org/msg22665.html
