Nested Class Summary
Nested classes/interfaces inherited from class hudson.ExtensionFinder
ExtensionFinder.DefaultGuiceExtensionAnnotation, ExtensionFinder.GuiceExtensionAnnotation<T extends Annotation>, ExtensionFinder.GuiceFinder, ExtensionFinder.Sezpoz
Constructors Constructor Description
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
find(Class<T> type, Hudson jenkins)Discover extensions of the given type.
scout(Class extensionType, Hudson hudson)Performs class initializations without creating instances.
public ExtensionComponentSet refresh()Rebuilds the internal index, if any, so that future
ExtensionFinder.find(Class, Hudson)calls will discover components newly added to
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
The behaviour is undefined if
ExtensionFinder.isRefreshable()is returning false.
SezPoz implements value-equality of
public <T> Collection<ExtensionComponent<T>> find(Class<T> type, Hudson jenkins)Description copied from class:
ExtensionFinderDiscover 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
- Specified by:
- Type Parameters:
T- The type of the extension points. This is not bound to
Descriptor, which by itself doesn't implement
ExtensionPointfor a historical reason.
jenkins- Jenkins whose behalf this extension finder is performing lookup.
- Can be empty but never null.
scoutDescription copied from class:
ExtensionFinderPerforms 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
That is, one thread can try to list extensions, which results in
ExtensionFinderloading 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.