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Difference between revisions of "Equinox Summit 2007 Results"

(ECF/Transports/Repositories)
(Framework Deep Dive)
Line 199: Line 199:
 
=== User Authentication ===
 
=== User Authentication ===
 
=== Framework Deep Dive ===
 
=== Framework Deep Dive ===
 +
 +
 +
Why is ContextClassLoader hard?
 +
--------------------------------
 +
 +
* in an enterprise situation you always know the context (this war, this ear).
 +
** all lower level libraries can get the context
 +
* OSGi has no clear entry point, you don't know who your client is
 +
* the specification is mute on the subject of CCL. It defaults to the system class loader
 +
* Spring OSGi does some manipulation of the CCL. Ensures that CCL can see bundle classes during activation. Can also manage CCL on service invocation (configurable to service client bundle, or service provider bundle)
 +
 +
ContextFinder
 +
--------------
 +
 +
Equinox has the ContextFinder that tries to find the context of who is calling. CCL is set to the ContextFinder. When forName is called, the *caller's* bundle is asked to load the class.
 +
 +
Note: you can use the context finder on other OSGi implementations.
 +
 +
BuddyPolicy
 +
------------
 +
 +
The Equinox buddy policy allows you to attach as a buddy of another bundle. e.g. to say that you are a buddy of Hibernate. Buddy policy does not required classes to be exported in order for them to be visible.
 +
 +
The "dependent" policy says anyone who depends on me directly or indirectly is a buddy.
 +
The "registered" policy forces bundles to say they want to be a buddy of X.
 +
 +
There is no way for a bundle A to declare that it wants access to private classes in bundle B.
 +
 +
What if bundle A doesn't know that bundle B will need to access it? For example, a framework creates this requirement without A's knowledge. Peter Kriens has a blog entry describing some possible solutions to this.
 +
 +
One proposal is to trap "ClassNotFoundException" and then go hunting for matching classes. Has a weakness that would force classes to be loaded this way to be exported. Can be problems if two bundles both have a private type with the same qualified name.
 +
 +
Some problems with the Buddy mechanism:
 +
 +
* If two buddies both have an internal class C, when the buddy bundle asks for C, which should it get?
 +
* Allows static references, not just dynamic ones. We noted that the Eclipse tooling will prevent static references if you develop using eclipse.
 +
* Class.forName caching
 +
 +
Class.forName
 +
--------------
 +
 +
Class.forName model is broken. Always call loadClass instead. Class.forName caches the resulting class (in the VM) in both the loading and calling class loader caches.
 +
 +
 +
Other ContextClassLoader issues:
 +
--------------------------------
 +
 +
Equinox sets the CCL to the ContextFinder. Inherited by spawned threads. If any bundle ever sets the CCL to something different and forgets to set it back, this thread will never recover. In some app servers it might recover on next request (but not all, e.g. OC4J).
 +
 +
System Bundle Fragments
 +
-------------------------
 +
 +
There are 2 types:
 +
 +
1. To supply extra classes to the framework implementation
 +
 +
  Added for conditional permission admin, types that are sensitive from a security perspective and should not be loaded from a bundle.
 +
 +
2. Boot class path extensions. (Adding things to VM boot classpath). For example, if you need to add types in the "java" namespace. This is not implemented in equinox. Requires vm restart.
 +
 +
An "Extension fragment" is an extension to the fragment classloader.
 +
 +
Other:
 +
-------
 +
 +
The EclipseStarter code is not pretty.
  
 
== Fourth breakout meeting ==
 
== Fourth breakout meeting ==

Revision as of 10:27, 26 September 2007

The Equinox Summit 2007 was arranged as a set of lightning talks and a series of breakout sessions. Each session had a number of parallel discussions with self-assigned and self-organizing participants. The groups then reported to a plenary session, summarizing their results and possibly adding more topics to be discussed in further breakouts.

Day One Results

First breakout meeting

Component Programming Models

  • Service helper: ideal for one-time use.
  • Spring
    • Injection model - no code to acquire the service
    • Client is handed a proxy to the service object
    • Framework manages binding of a real service to the proxy dynamically
    • Distinguish between mandatory and optional service requirements
      • Mandatory: your bundle isn't started until all the mandatory services are available
      • This only guarantees availability at a moment in time: at the moment of startup all mandatory services are available, but they could disappear after that moment.
      • If a mandatory service goes away, the services exported by the bundle needing the service is unregistered.
    • For stateful services, there is a listener model - bind an unbind events occur as service implementations arrive and depart
    • It would be interesting to be able to declare a default service implementation that would be used whenever no real service is available
  • Spring and DS require eager activation, but only for service producers. Many bundles are just service consumers, and so they can be lazily started
  • Requirements for Spring service support: Spring core, Spring AOP, a few other essential Spring core pieces
  • Service Application Toolkit: IBM toolkit for making it easier to work with OSGi services
  • How do we reconcile and combine the various component toolkits available: Spring, DS, SAT, extension registry
  • Spring initializes the app context asynchronously. Typical Eclipse programming model assumes that all initialization has completed by the time any classes are loaded in that bundle.
  • To be scalable, we need a model where service wiring is persisted across sessions, so we don't have the massive event storm of services being started and bound as the system comes up.
  • Most bundles are POJO - how do they specify that they need Spring or some other component system to be available at runtime? Ideally 95% of bundles don't know or care about the active component system - but they need some component system to be around at runtime to inject the services they need.
  • Can we come up with a common syntax where a bundle can specify its service and extension registry imports/exports, and be agnostic about the runtime that will parse it and provide the runtime capabilities.
  • Scoping: extension registry / services are global - how can I publish extensions/services that are only available in a particular scope* only particular set of bundles have access to it. In J2EE world, sometimes only want to register/bind services within a particular web app. Scoped registries - local versus global extension registry.

p2 Design Deep Dive

Interesting topics:

  • Profiles/ hierarchy of profiles
  • Headless agent; managed installs
  • Everything is possible
  • Version range lineups,
  • Security? JAAS
  • Resolver - where does it go? when?
  • Plugable download manager
  • Plugable communications - within ECF. replacing ECF?

Tooling (builds)

  • Enhancements to current export
    • pack/unpack/sign support
    • export to multiple targets (exporting platform dependent fragments)
  • Current Export
    • leave behind generated files for debugging purposes
  • Project Builder (can we get this into the pde.incubator)
    • a new builder project (like existing update site project)
    • Provides a mechanism to bootstrap from export to headless build
    • generates artifacts (features/build.properties/customTargets.xml/allElements.xml) that are input into pde.build
    • provides forms/editors (or wizards) to expose pde.build options
    • Consider different inputs : .product file, launch configuration
    • enable gradual discovery of customizability: customTargets.xml, plugin level build callbacks.
    • Synchronization between workspace and plugin level build properties.
  • PDE/Build proper: selected refactorings to make project builder easier
    • remove need for allElements.xml

Server Side Web apps++

Second breakout meeting

API Tooling

  • Clarify definition of API (what is API, what is API compatibility)
    • Public API (as defined by Jeem's API white paper)
    • Internal code
    • Provisional API
    • SPI - Service provider interfaces
    • Eclipse-specific API such as extension point ids, other data in extension/extension-point markup
  • Tool to annotate code with API rules (javadoc tags that specify if a class may be implemented, instantiated, etc)
  • Build API rule file from javadoc tags
  • Want both IDE integration, and headless build usage
  • Scalability
    • Be able to run API tools on smaller components/bundles/pieces rather than the whole world
    • Store results in various forms: XML files, or perhaps database for large scale use
    • API data may be stored locally or remotely
  • Discussion on whether API rule files could replace JDT access restrictions. It's really a super-set of access rules, can express things that acess rules cannot
  • API usage reports: could have simple HTML pages, or Eclipse integration into views/editors, like the Emma Eclipse plugin does for coverage data
  • Support for API tooling in other languages and .so/DLL files
  • Use of reflection is problematic because it's hard to detect programmaticaly

Server Side Remote Management

Provisioning will handle and cover much of the use case around managing the provisioning of servers.

The notion of a "nano" entity for initial provisioning will be useful,

A entity that can be tickled to check, verify and rectify the state of an equinox runtime.

There is not much available for managing totally non-running systems. Systems will need to have something running to talk to.

There are several frameworks to add on top of running osgi systems for managing the installs JMX, MX4J, Remote Console, DMTAdmin.

Things to look into: -DMT Admin: There is no spec available? -OSGi Monitoring Spec.

P2 Security

Day Two Results

Third breakout meeting

ECF/Transports/Repositories

We started with a discussion of requirements for the p2 download manager and transport layer:

  • Robustness of download manager
    • Mirroring
    • Different repos have different characteristics - some repos can support many connections
    • Adaptive re-prioritization - if you are downloading 1GB of data, you may need to switch to a different mirror dynamically
    • Weighting of repositories based on latency, availability, etc.
    • For downloading many small pieces, may be more efficient to combine them into a single large artifact for download purposes (minimizing round-trips)
  • Bit-torrent:
    • Not good for many small files
    • Great for Eclipse release periods where there are large download peaks.
    • Could work well in a corporate environment where a large group of people are provisioning the same software around the same time.
  • Where do we embed all this intelligence - in a single uber-smart download manager, or should some of that smarts be hidden away in repository implementations? Could have a single smart repo that acts as a facade to a group of backing repos.

ECF:

  • Scott: ECF is just intended to be a slim asynchronous transfer API - while some of these details could be handled at the transport level, some of this complexity should be built in a layer above ECF
  • Requirement for ECF: be able to introspect download stats in order to make adaptive decisions, alter repo weightings, etc.
  • Also need new API from ECF to start artifact downloads at a particular offset in an artifact. This is needed both for resume of downloads, and for multi-threaded download of a single file (each thread downloads a chunk, potentially from different mirrors, and then chunks are reassembled upon completion of download)

Getting more concrete on the design and how the pieces fit together. First cut: Intelligence and design making largely in download manager. However, repository implementations need to be able to answer various questions in order for the download manager to be able to make its decisions:

  • Memory and disk space requirements
  • CPU time requirements
  • Latency/throughput of transport
  • Download manager also needs to account for local machine characteristics - how many concurrent downloads can it run, etc

Aiming for a relatively simple download manager with pluggable download strategies. Can start with a simple d/l strategy much like our current implementation. Then be able to plug in a much fancier d/l strategy that does mult-threading, adaptive behaviour, etc.

Work items:

  • Modify current d/l manager to have pluggable strategies
  • API for asynchronous interaction with repositories
  • API for querying progress of repos
  • Repo API for starting artifact downloads at some offset in the artifact

p2 Tooling

"Everything is possible with enough contributions"

self-hosting has been difficult historically

  • provision from workspace
  • imagine target platform + your workspace are one big repository
  • push from workspace
  • "Export -> metadata repository"

build tooling

  • ability to batch IU generation
  • are we generating a repository as an archive?
  • all plugins ar epushed and published in a repository
  • archiving of a repository is a build operation
  • installing agent and installing and downloading a runnable piece should give the same thing

deployment tooling

  • when do we integrate the generator during build/exporting?

authoring tooling

  • long-term we want people to author IUs (editors)
  • probably not for 3.4
  • for 3.4, we will probably have some sort of feature.xml -> IU translation

development tooling

  • hints, IUs, feature.xml -> generator => IUs

repository tooling

  • manage content (browsing, expiration)
  • simple APIs for repositories (addIU, removeIU)

other concerns

  • remote generation of metadata and remote management of clients
  • what is the "runtime"? is provisioning included in "runtime"?
  • how do we manage remote runtimes? DMT admin?
  • workspace would be a "management console" using a specific API
  • No cost for people doing plain plugin development
    • pull model: running instance pulls from workspace implicitly-generated metadata
  • Are IUs self-contained?
    • we have no support for translation right now
    • currently we're replicating common information across IUs
  • How do we do translation of IUs?
    • tooling support
  • Dynamic tooling is a separate topic
    • are my bundles really dynamic?
    • will removing my bundles remove them completely?
  • feature transitioning (branding, icons, etc.)

User Authentication

Framework Deep Dive

Why is ContextClassLoader hard?


  • in an enterprise situation you always know the context (this war, this ear).
    • all lower level libraries can get the context
  • OSGi has no clear entry point, you don't know who your client is
  • the specification is mute on the subject of CCL. It defaults to the system class loader
  • Spring OSGi does some manipulation of the CCL. Ensures that CCL can see bundle classes during activation. Can also manage CCL on service invocation (configurable to service client bundle, or service provider bundle)

ContextFinder


Equinox has the ContextFinder that tries to find the context of who is calling. CCL is set to the ContextFinder. When forName is called, the *caller's* bundle is asked to load the class.

Note: you can use the context finder on other OSGi implementations.

BuddyPolicy


The Equinox buddy policy allows you to attach as a buddy of another bundle. e.g. to say that you are a buddy of Hibernate. Buddy policy does not required classes to be exported in order for them to be visible.

The "dependent" policy says anyone who depends on me directly or indirectly is a buddy. The "registered" policy forces bundles to say they want to be a buddy of X.

There is no way for a bundle A to declare that it wants access to private classes in bundle B.

What if bundle A doesn't know that bundle B will need to access it? For example, a framework creates this requirement without A's knowledge. Peter Kriens has a blog entry describing some possible solutions to this.

One proposal is to trap "ClassNotFoundException" and then go hunting for matching classes. Has a weakness that would force classes to be loaded this way to be exported. Can be problems if two bundles both have a private type with the same qualified name.

Some problems with the Buddy mechanism:

  • If two buddies both have an internal class C, when the buddy bundle asks for C, which should it get?
  • Allows static references, not just dynamic ones. We noted that the Eclipse tooling will prevent static references if you develop using eclipse.
  • Class.forName caching

Class.forName


Class.forName model is broken. Always call loadClass instead. Class.forName caches the resulting class (in the VM) in both the loading and calling class loader caches.


Other ContextClassLoader issues:


Equinox sets the CCL to the ContextFinder. Inherited by spawned threads. If any bundle ever sets the CCL to something different and forgets to set it back, this thread will never recover. In some app servers it might recover on next request (but not all, e.g. OC4J).

System Bundle Fragments


There are 2 types:

1. To supply extra classes to the framework implementation

 Added for conditional permission admin, types that are sensitive from a security perspective and should not be loaded from a bundle.

2. Boot class path extensions. (Adding things to VM boot classpath). For example, if you need to add types in the "java" namespace. This is not implemented in equinox. Requires vm restart.

An "Extension fragment" is an extension to the fragment classloader.

Other:


The EclipseStarter code is not pretty.

Fourth breakout meeting

Topic 1

Topic 2

Topic 3

Topic 4

Fifth breakout meeting

Topic 1

Topic 2

Topic 3

Topic 4

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