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