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< Equinox‎ | p2
Revision as of 13:15, 12 September 2011 by (Talk | contribs) (A start, based on questions seen in the p2 forum and dev list)

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What is p2?

p2 is a provisioning platform for Eclipse-based applications.  It replaces the older Update Manager as the mechanism for managing an Eclipse installation.  Provisioning is the act of finding and installing new functionality, and updating or removing existing functionality; it is distinct from building.

p2 manages artifacts, such as bundles, features, and products; you can think of these as bags of bytes.  p2 not only stores these artifacts, it also stores metadata about these artifacts, such as version information, cryptographic signatures, dependencies between artifacts, platform specifics, and special installation requirements.

Every p2 artifact is uniquely identified by an identifier and version number. For example, the Equinox OSGi container from the Indigo release is a bundle whose identifier is org.eclipse.osgi and version 3.7.0.v20110110.

An artifact is made available to p2 by publishing the artifact to a repository, a process that also adds any metadata about the artifact. p2 comes with several publishers that know how to extract metadata for bundles, features, and products. Most Eclipse build systems (e.g., Tycho, Buckminister, PDE/Build) can automatically publish the artifacts during a build. Other publishers could be created using p2's APIs to handle other types of artifacts (e.g., Windows DLLs).

The p2 Director is responsible for installing a set of artifacts. The Director uses the metadata about an artifact, called an installable unit or IU, to determine how the artifact should be installed and to include any dependencies of those artifacts. Thus installing a product requires installing its associated features, which requires installing the specified bundles; installing the product also requires installing the platform-specific executable.

The Director is a wrapper around several lower-level p2 components. A Profile records the IUs installed. An Agent uses the Planner to determine the IUs to be managed, and uses the Engine to actually perform the sequence of installation steps. These installation steps are handled by touchpoints specific to each type of artifact.

See the p2 concepts guide for more details about these different terms.

Accessing Repositories

= Why won't p2 replace an updated bundle in a repository?

p2 assumes that two artifacts with the exact same identifier and version are the same artifact. Once an artifact has been published to a repository, it cannot be replaced. This restriction acts both as a performance optimization, to avoid unnecessary downloads, as well as a consistency check. For example, the Equinox OSGi container from the Indigo release is a bundle whose identifier is org.eclipse.osgi and version 3.7.0.v20110110. Any update to an artifact must be published with a new version number.

How can I find the features that include a particular bundle?

Using the p2 Query Language from the OSGi console, substitute the appropriate repository URL and BUNDLEID:

$ eclipse -console -noSplash -noExit -vmargs -Declipse.application.launchDefault=false
osgi> provaddrepo
osgi> provlpquery * "select(parent |[''] == true && parent.requirements.exists(rc | everything.exists(iu | iu ~= rc && == 'BUNDLEID')))" true

Credit to Paul Webster.


How do I incorporate p2 into my RCP app?

There are three approaches for integrating p2 into your app.

The first approach, called the "User Interface API", is actually a framework for managing updates, complete with wizards and configurable scheduling. It is the same framework used by Eclipse's update management. Your application provides policies and other configuration values to guide this framework. Note that this API has a dependency on the Eclipse 3.x Platform UI (org.eclipse.ui), and requires the Platform UI compatibility layer for applications using the Eclipse 4 Application Platform. We have provided a worked example in the article on "Adding Self-Update to an RCP Application".

The second approach is to use p2's higher-level Operation APIs to drive updates. These APIs provide a thin layer over the Core APIs (described next) to describe updates as an atomic install, uninstall, or update of an artifact. are more intended for headless applications. We have provided a worked example in the article on "Adding Self-Update to an RCP Application".

The third and final approach, is to use p2's Core APIs, where you interact with the p2 agent directly. This is the most powerful, but also most complex, of the possible approaches.

See the worked examples in the article on "Adding Self-Update to an RCP Application", and the example applications.

Please note that we do not recommend that you invoke the p2 director from your application with a shell call (e.g., "app.exe -application org.eclipse.equinox.p2.director …")!

Why am I getting errors trying when access p2 services?

p2 relies on the OSGi Declarative Services feature. You must include and start the org.eclipse.equinox.ds bundle.

Why aren't bundles being removed when their associated feature has been removed?

There are two aspects to this problem.  First, you must ensure that features are recorded when installing a feature by specifying the "org.eclipse.update.install.features=true" property, such that the bundles have a recorded dependency against the feature.  Second, you must invoke the p2 garbage collector.[1]

IProfileRegistry profileRegistry = (IProfileRegistry) ServiceHelper.getService(Activator.getContext(), IProfileRegistry.class.getName());
if (profileRegistry == null)
throw new RuntimeException("Unable to acquire the profile registry service.");
// can also use IProfileRegistry.SELF for the current profile
IProfile profile = profileRegistry.getProfile("SDKProfile");
new GarbageCollector().runGC(profile);

You can also invoke the garbage collector application:[2]

eclipse -application org.eclipse.equinox.p2.garbagecollector.application -profile SDKProfile 

Where can I learn more?

  • The p2 wiki
  • Pascal Rapicault has a number of slide decks on 



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