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236 lines
10 KiB
Java
236 lines
10 KiB
Java
/*
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* The MIT License
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*
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* Copyright (c) 2004-2010, Sun Microsystems, Inc., InfraDNA, Inc.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package hudson;
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import com.google.common.collect.ImmutableList;
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import hudson.init.InitMilestone;
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import net.java.sezpoz.Index;
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import net.java.sezpoz.IndexItem;
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import hudson.model.Hudson;
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import hudson.model.Descriptor;
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import org.kohsuke.accmod.Restricted;
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import org.kohsuke.accmod.restrictions.NoExternalUse;
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import java.util.Collections;
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import java.util.logging.Logger;
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import java.util.logging.Level;
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import java.util.List;
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import java.util.ArrayList;
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import java.util.Collection;
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import java.lang.reflect.AnnotatedElement;
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import java.lang.reflect.Field;
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import java.lang.reflect.Method;
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/**
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* Discovers the implementations of an extension point.
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*
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* <p>
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* This extension point allows you to write your implementations of {@link ExtensionPoint}s
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* in arbitrary DI containers, and have Hudson discover them.
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*
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* <p>
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* {@link ExtensionFinder} itself is an extension point, but to avoid infinite recursion,
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* Hudson discovers {@link ExtensionFinder}s through {@link Sezpoz} and that alone.
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*
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* @author Kohsuke Kawaguchi
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* @since 1.286
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*/
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public abstract class ExtensionFinder implements ExtensionPoint {
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/**
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* @deprecated as of 1.356
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* Use and implement {@link #find(Class, Hudson)} that allows us to put some metadata.
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*/
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@Restricted(NoExternalUse.class)
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public <T> Collection<T> findExtensions(Class<T> type, Hudson hudson) {
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return Collections.emptyList();
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}
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/**
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* Discover extensions of the given type.
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*
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* <p>
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* This method is called only once per the given type after all the plugins are loaded,
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* so implementations need not worry about caching.
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*
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* @param <T>
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* The type of the extension points. This is not bound to {@link ExtensionPoint} because
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* of {@link Descriptor}, which by itself doesn't implement {@link ExtensionPoint} for
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* a historical reason.
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* @param hudson
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* Hudson whose behalf this extension finder is performing lookup.
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* @return
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* Can be empty but never null.
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* @since 1.356
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* Older implementations provide {@link #findExtensions(Class, Hudson)}
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*/
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public abstract <T> Collection<ExtensionComponent<T>> find(Class<T> type, Hudson hudson);
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/**
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* A pointless function to work around what appears to be a HotSpot problem. See HUDSON-5756 and bug 6933067
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* on BugParade for more details.
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*/
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public <T> Collection<ExtensionComponent<T>> _find(Class<T> type, Hudson hudson) {
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return find(type,hudson);
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}
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/**
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* Performs class initializations without creating instances.
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*
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* If two threads try to initialize classes in the opposite order, a dead lock will ensue,
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* and we can get into a similar situation with {@link ExtensionFinder}s.
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*
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* <p>
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* That is, one thread can try to list extensions, which results in {@link ExtensionFinder}
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* loading and initializing classes. This happens inside a context of a lock, so that
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* another thread that tries to list the same extensions don't end up creating different
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* extension instances. So this activity locks extension list first, then class initialization next.
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*
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* <p>
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* In the mean time, another thread can load and initialize a class, and that initialization
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* can eventually results in listing up extensions, for example through static initializer.
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* Such activity locks class initialization first, then locks extension list.
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*
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* <p>
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* This inconsistent locking order results in a dead lock, you see.
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*
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* <p>
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* So to reduce the likelihood, this method is called in prior to {@link #find(Class, Hudson)} invocation,
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* but from outside the lock. The implementation is expected to perform all the class initialization activities
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* from here.
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*
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* <p>
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* See http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6459208 for how to force a class initialization.
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* Also see http://kohsuke.org/2010/09/01/deadlock-that-you-cant-avoid/ for how class initialization
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* can results in a dead lock.
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*/
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public void scout(Class extensionType, Hudson hudson) {
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}
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/**
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* The default implementation that looks for the {@link Extension} marker.
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*
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* <p>
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* Uses Sezpoz as the underlying mechanism.
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*/
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@Extension
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public static final class Sezpoz extends ExtensionFinder {
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private volatile List<IndexItem<Extension,Object>> indices;
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/**
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* Loads indices (ideally once but as few times as possible), then reuse them later.
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* {@link ExtensionList#ensureLoaded()} guarantees that this method won't be called until
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* {@link InitMilestone#PLUGINS_PREPARED} is attained, so this method is guaranteed to
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* see all the classes and indices.
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*/
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private List<IndexItem<Extension,Object>> getIndices() {
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// this method cannot be synchronized because of a dead lock possibility in the following order of events:
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// 1. thread X can start listing indices, locking this object 'SZ'
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// 2. thread Y starts loading a class, locking a classloader 'CL'
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// 3. thread X needs to load a class, now blocked on CL
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// 4. thread Y decides to load extensions, now blocked on SZ.
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// 5. dead lock
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if (indices==null) {
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ClassLoader cl = Hudson.getInstance().getPluginManager().uberClassLoader;
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indices = ImmutableList.copyOf(Index.load(Extension.class, Object.class, cl));
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}
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return indices;
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}
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public <T> Collection<ExtensionComponent<T>> find(Class<T> type, Hudson hudson) {
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List<ExtensionComponent<T>> result = new ArrayList<ExtensionComponent<T>>();
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for (IndexItem<Extension,Object> item : getIndices()) {
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try {
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AnnotatedElement e = item.element();
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Class<?> extType;
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if (e instanceof Class) {
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extType = (Class) e;
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} else
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if (e instanceof Field) {
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extType = ((Field)e).getType();
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} else
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if (e instanceof Method) {
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extType = ((Method)e).getReturnType();
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} else
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throw new AssertionError();
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if(type.isAssignableFrom(extType)) {
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Object instance = item.instance();
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if(instance!=null)
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result.add(new ExtensionComponent<T>(type.cast(instance),item.annotation()));
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}
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} catch (LinkageError e) {
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// sometimes the instantiation fails in an indirect classloading failure,
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// which results in a LinkageError
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LOGGER.log(logLevel(item), "Failed to load "+item.className(), e);
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} catch (InstantiationException e) {
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LOGGER.log(logLevel(item), "Failed to load "+item.className(), e);
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}
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}
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return result;
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}
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@Override
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public void scout(Class extensionType, Hudson hudson) {
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for (IndexItem<Extension,Object> item : getIndices()) {
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try {
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// we might end up having multiple threads concurrently calling into element(),
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// but we can't synchronize this --- if we do, the one thread that's supposed to load a class
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// can block while other threads wait for the entry into the element call().
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// looking at the sezpoz code, it should be safe to do so
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AnnotatedElement e = item.element();
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Class<?> extType;
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if (e instanceof Class) {
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extType = (Class) e;
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} else
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if (e instanceof Field) {
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extType = ((Field)e).getType();
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} else
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if (e instanceof Method) {
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extType = ((Method)e).getReturnType();
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} else
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throw new AssertionError();
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// according to http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6459208
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// this appears to be the only way to force a class initialization
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Class.forName(extType.getName(),true,extType.getClassLoader());
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} catch (InstantiationException e) {
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LOGGER.log(logLevel(item), "Failed to scout "+item.className(), e);
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} catch (ClassNotFoundException e) {
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LOGGER.log(logLevel(item), "Failed to scout "+item.className(), e);
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} catch (LinkageError e) {
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LOGGER.log(logLevel(item), "Failed to scout "+item.className(), e);
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}
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}
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}
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private Level logLevel(IndexItem<Extension, Object> item) {
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return item.annotation().optional() ? Level.FINE : Level.WARNING;
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}
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}
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private static final Logger LOGGER = Logger.getLogger(ExtensionFinder.class.getName());
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}
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