package net.bytebuddy.dynamic;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.logging.Logger;
/**
* <p>
* This nexus is a global dispatcher for initializing classes with
* {@link net.bytebuddy.implementation.LoadedTypeInitializer}s. To do so, this class is to be loaded
* by the system class loader in an explicit manner. Any instrumented class is then injected a code
* block into its static type initializer that makes a call to this very same nexus which had the
* loaded type initializer registered before hand.
* </p>
* <p>
* <b>Note</b>: Availability of the {@link Nexus} class and its injection into the system class loader
* can be disabled entirely by setting the {@link Nexus#PROPERTY} system property to {@code false}.
* </p>
* <p>
* <b>Important</b>: The nexus must never be accessed directly but only by the {@link NexusAccessor}
* which makes sure that the nexus is loaded by the system class loader. Otherwise, a class might not
* be able to initialize itself if it is loaded by different class loader that does not have the
* system class loader in its hierarchy.
* </p>
*/
public class Nexus extends WeakReference<ClassLoader> {
/**
* A system property that allows to disable the use of the {@link Nexus} class which is normally injected into the system class loader.
*/
public static final String PROPERTY = "net.bytebuddy.nexus.disabled";
/**
* An type-safe constant for a non-operational reference queue.
*/
protected static final ReferenceQueue<ClassLoader> NO_QUEUE = null;
/**
* A map of keys identifying a loaded type by its name and class loader mapping their
* potential {@link net.bytebuddy.implementation.LoadedTypeInitializer} where the class
* loader of these initializers is however irrelevant.
*/
private static final ConcurrentMap<Nexus, Object> TYPE_INITIALIZERS = new ConcurrentHashMap<Nexus, Object>();
/**
* The name of a type for which a loaded type initializer is registered.
*/
private final String name;
/**
* The class loader's hash code upon registration.
*/
private final int classLoaderHashCode;
/**
* A random value that uniquely identifies a Nexus entry in order to avoid conflicts when
* applying the self-initialization strategy in multiple transformations.
*/
private final int identification;
/**
* Creates a key for identifying a loaded type initializer.
*
* @param type The loaded type for which a key is to be created.
* @param identification An identification for the initializer to run.
*/
private Nexus(Class<?> type, int identification) {
this(nonAnonymous(type.getName()), type.getClassLoader(), NO_QUEUE, identification);
}
/**
* Creates a key for identifying a loaded type initializer.
*
* @param name The name of a type for which a loaded type initializer is registered.
* @param classLoader The class loader for which a loaded type initializer is registered.
* @param referenceQueue The reference queue to notify upon the class loader's collection or {@code null} if no queue should be notified.
* @param identification An identification for the initializer to run.
*/
private Nexus(String name, ClassLoader classLoader, ReferenceQueue<? super ClassLoader> referenceQueue, int identification) {
super(classLoader, classLoader == null
? null
: referenceQueue);
this.name = name;
classLoaderHashCode = System.identityHashCode(classLoader);
this.identification = identification;
}
/**
* Normalizes a type name if it is loaded by an anonymous class loader.
*
* @param typeName The name as returned by {@link Class#getName()}.
* @return The non-anonymous name of the given class.
*/
private static String nonAnonymous(String typeName) {
int anonymousLoaderIndex = typeName.indexOf('/');
return anonymousLoaderIndex == -1
? typeName
: typeName.substring(0, anonymousLoaderIndex);
}
/**
* <p>
* Initializes a loaded type. This method must only be invoked via the system class loader.
* </p>
* <p>
* <b>Important</b>: This method must never be called directly but only by using a {@link NexusAccessor.InitializationAppender} which enforces to
* access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded
* by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by
* different class loaders, too. Any access of the instance is done using Java reflection instead.
* </p>
*
* @param type The loaded type to initialize.
* @param identification An identification for the initializer to run.
* @throws Exception If an exception occurs.
*/
@SuppressWarnings("unused")
public static void initialize(Class<?> type, int identification) throws Exception {
Object typeInitializer = TYPE_INITIALIZERS.remove(new Nexus(type, identification));
if (typeInitializer != null) {
typeInitializer.getClass().getMethod("onLoad", Class.class).invoke(typeInitializer, type);
}
}
/**
* <p>
* Registers a new loaded type initializer.
* </p>
* <p>
* <b>Important</b>: This method must never be called directly but only by using a {@link NexusAccessor} which enforces to access this class
* for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class
* loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders,
* too. Any access of the instance is done using Java reflection instead.
* </p>
*
* @param name The name of the type for the loaded type initializer.
* @param classLoader The class loader of the type for the loaded type initializer.
* @param referenceQueue The reference queue to notify upon the class loader's collection which will be enqueued a reference which can be
* handed to {@link Nexus#clean(Reference)} or {@code null} if no reference queue should be notified.
* @param identification An identification for the initializer to run.
* @param typeInitializer The type initializer to register. The initializer must be an instance
* of {@link net.bytebuddy.implementation.LoadedTypeInitializer} where
* it does however not matter which class loader loaded this latter type.
*/
public static void register(String name, ClassLoader classLoader, ReferenceQueue<? super ClassLoader> referenceQueue, int identification, Object typeInitializer) {
if (TYPE_INITIALIZERS.put(new Nexus(name, classLoader, referenceQueue, identification), typeInitializer) != null) {
Logger.getLogger("net.bytebuddy").warning("Initializer with id " + identification + " is already registered for " + name);
}
}
/**
* <p>
* Cleans any stale entries from this nexus. Entries are considered stale if their class loader was collected before a class was initialized.
* </p>
* <p>
* <b>Important</b>: This method must never be called directly but only by using a {@link NexusAccessor} which enforces to access this class
* for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class
* loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders,
* too. Any access of the instance is done using Java reflection instead.
* </p>
*
* @param reference The stale reference to clean.
*/
public static void clean(Reference<? super ClassLoader> reference) {
TYPE_INITIALIZERS.remove(reference);
}
@Override
public boolean equals(Object object) {
if (this == object) return true;
if (object == null || getClass() != object.getClass()) return false;
Nexus nexus = (Nexus) object;
return classLoaderHashCode == nexus.classLoaderHashCode
&& identification == nexus.identification
&& name.equals(nexus.name)
&& get() == nexus.get();
}
@Override
public int hashCode() {
int result = name.hashCode();
result = 31 * result + classLoaderHashCode;
result = 31 * result + identification;
return result;
}
@Override
public String toString() {
return "Nexus{" +
"name='" + name + '\'' +
", classLoaderHashCode=" + classLoaderHashCode +
", identification=" + identification +
", classLoader=" + get() +
'}';
}
}