hudson

Class ExtensionFinder.Sezpoz

java.lang.Object

hudson.ExtensionFinder

hudson.ExtensionFinder.Sezpoz

All Implemented Interfaces:

ExtensionPoint

Enclosing class:

ExtensionFinder

public static final class ExtensionFinder.Sezpoz
extends ExtensionFinder

The bootstrap implementation that looks for the Extension marker.

Uses Sezpoz as the underlying mechanism.

Nested Class Summary

Nested classes/interfaces inherited from class hudson.ExtensionFinder

ExtensionFinder.DefaultGuiceExtensionAnnotation, ExtensionFinder.GuiceExtensionAnnotation<T extends Annotation>, ExtensionFinder.GuiceFinder, ExtensionFinder.Sezpoz

Nested classes/interfaces inherited from interface hudson.ExtensionPoint

ExtensionPoint.LegacyInstancesAreScopedToHudson

Constructor Summary

Constructors

Constructor and Description
Sezpoz()

Method Summary

Modifier and Type	Method and Description
<T> Collection<ExtensionComponent<T>>	find(Class<T> type, Hudson jenkins) Discover extensions of the given type.
ExtensionComponentSet	refresh() Rebuilds the internal index, if any, so that future ExtensionFinder.find(Class, Hudson) calls will discover components newly added to PluginManager.uberClassLoader.
void	scout(Class extensionType, Hudson hudson) Performs class initializations without creating instances.

Methods inherited from class hudson.ExtensionFinder

_find, findExtensions, isRefreshable

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Sezpoz

public Sezpoz()

Method Detail

refresh

public ExtensionComponentSet refresh()

Rebuilds the internal index, if any, so that future ExtensionFinder.find(Class, Hudson) calls will discover components newly added to PluginManager.uberClassLoader.

The point of the refresh operation is not to disrupt instances of already loaded ExtensionComponents, and only instantiate those that are new. Otherwise this will break the singleton semantics of various objects, such as Descriptors.

The behaviour is undefined if ExtensionFinder.isRefreshable() is returning false.

SezPoz implements value-equality of IndexItem, so

Specified by:

refresh in class ExtensionFinder

Returns:

never null

See Also:

ExtensionFinder.isRefreshable()

find

public <T> Collection<ExtensionComponent<T>> find(Class<T> type,
                                                  Hudson jenkins)

Description copied from class: ExtensionFinder

Discover extensions of the given type.

This method is called only once per the given type after all the plugins are loaded, so implementations need not worry about caching.

This method should return all the known components at the time of the call, including those that are discovered later via ExtensionFinder.refresh(), even though those components are separately returned in ExtensionComponentSet.

Specified by:

find in class ExtensionFinder

Type Parameters:

T - The type of the extension points. This is not bound to ExtensionPoint because of Descriptor, which by itself doesn't implement ExtensionPoint for a historical reason.

jenkins - Jenkins whose behalf this extension finder is performing lookup.

Returns:

Can be empty but never null.

scout

public void scout(Class extensionType,
                  Hudson hudson)

Description copied from class: ExtensionFinder

Performs class initializations without creating instances. If two threads try to initialize classes in the opposite order, a dead lock will ensue, and we can get into a similar situation with ExtensionFinders.

That is, one thread can try to list extensions, which results in ExtensionFinder loading and initializing classes. This happens inside a context of a lock, so that another thread that tries to list the same extensions don't end up creating different extension instances. So this activity locks extension list first, then class initialization next.

In the mean time, another thread can load and initialize a class, and that initialization can eventually results in listing up extensions, for example through static initializer. Such activity locks class initialization first, then locks extension list.

This inconsistent locking order results in a dead lock, you see.

So to reduce the likelihood, this method is called in prior to ExtensionFinder.find(Class,Hudson) invocation, but from outside the lock. The implementation is expected to perform all the class initialization activities from here.

See https://bugs.openjdk.java.net/browse/JDK-4993813 for how to force a class initialization. Also see http://kohsuke.org/2010/09/01/deadlock-that-you-cant-avoid/ for how class initialization can results in a dead lock.

Overrides:

scout in class ExtensionFinder