package net.bytebuddy.dynamic;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import lombok.EqualsAndHashCode;
import net.bytebuddy.description.method.MethodDescription;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.dynamic.loading.ClassInjector;
import net.bytebuddy.dynamic.loading.ClassLoadingStrategy;
import net.bytebuddy.implementation.Implementation;
import net.bytebuddy.implementation.LoadedTypeInitializer;
import net.bytebuddy.implementation.bytecode.ByteCodeAppender;
import net.bytebuddy.implementation.bytecode.Removal;
import net.bytebuddy.implementation.bytecode.StackManipulation;
import net.bytebuddy.implementation.bytecode.collection.ArrayFactory;
import net.bytebuddy.implementation.bytecode.constant.ClassConstant;
import net.bytebuddy.implementation.bytecode.constant.IntegerConstant;
import net.bytebuddy.implementation.bytecode.constant.NullConstant;
import net.bytebuddy.implementation.bytecode.constant.TextConstant;
import net.bytebuddy.implementation.bytecode.member.MethodInvocation;
import org.objectweb.asm.MethodVisitor;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Arrays;
import java.util.Collections;
/**
* The Nexus accessor is creating a VM-global singleton {@link Nexus} such that it can be seen by all class loaders of
* a virtual machine. Furthermore, it provides an API to access this global instance.
*/
@EqualsAndHashCode
public class NexusAccessor {
/**
* The dispatcher to use.
*/
private static final Dispatcher DISPATCHER = AccessController.doPrivileged(Dispatcher.CreationAction.INSTANCE);
/**
* The reference queue that is notified upon a GC eligible {@link Nexus} entry or {@code null} if no such queue should be notified.
*/
private final ReferenceQueue<? super ClassLoader> referenceQueue;
/**
* Creates a new accessor for the {@link Nexus} without any active management of stale references within a nexus.
*/
public NexusAccessor() {
this(Nexus.NO_QUEUE);
}
/**
* Creates a new accessor for a {@link Nexus} where any GC eligible are enqueued to the supplid reference queue. Any such enqueued
* reference can be explicitly removed from the nexus via the {@link NexusAccessor#clean(Reference)} method. Nexus entries can
* become stale if a class loader is garbage collected after a class was loaded but before a class was initialized.
*
* @param referenceQueue The reference queue onto which stale references should be enqueued or {@code null} if no reference queue
* should be notified.
*/
public NexusAccessor(ReferenceQueue<? super ClassLoader> referenceQueue) {
this.referenceQueue = referenceQueue;
}
/**
* Checks if this {@link NexusAccessor} is capable of registering loaded type initializers.
*
* @return {@code true} if this accessor is alive.
*/
public static boolean isAlive() {
return DISPATCHER.isAlive();
}
/**
* Removes a stale entries that are registered in the {@link Nexus}. Entries can become stale if a class is loaded but never initialized
* prior to its garbage collection. As all class loaders within a nexus are only referenced weakly, such class loaders are always garbage
* collected. However, the initialization data stored by Byte Buddy does not become eligible which is why it needs to be cleaned explicitly.
*
* @param reference The reference to remove. References are collected via a reference queue that is supplied to the {@link NexusAccessor}.
*/
public static void clean(Reference<? extends ClassLoader> reference) {
DISPATCHER.clean(reference);
}
/**
* Registers a loaded type initializer in Byte Buddy's {@link Nexus} which is injected into the system class loader.
*
* @param name The binary name of the class.
* @param classLoader The class's class loader.
* @param identification The id used for identifying the loaded type initializer that was added to the {@link Nexus}.
* @param loadedTypeInitializer The loaded type initializer to make available via the {@link Nexus}.
*/
public void register(String name, ClassLoader classLoader, int identification, LoadedTypeInitializer loadedTypeInitializer) {
if (loadedTypeInitializer.isAlive()) {
DISPATCHER.register(name, classLoader, referenceQueue, identification, loadedTypeInitializer);
}
}
/**
* An initialization appender that looks up a loaded type initializer from Byte Buddy's {@link Nexus}.
*/
@EqualsAndHashCode
public static class InitializationAppender implements ByteCodeAppender {
/**
* The id used for identifying the loaded type initializer that was added to the {@link Nexus}.
*/
private final int identification;
/**
* Creates a new initialization appender.
*
* @param identification The id used for identifying the loaded type initializer that was added to the {@link Nexus}.
*/
public InitializationAppender(int identification) {
this.identification = identification;
}
@Override
public Size apply(MethodVisitor methodVisitor, Implementation.Context implementationContext, MethodDescription instrumentedMethod) {
try {
return new ByteCodeAppender.Simple(new StackManipulation.Compound(
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(ClassLoader.class.getMethod("getSystemClassLoader"))),
new TextConstant(Nexus.class.getName()),
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(ClassLoader.class.getMethod("loadClass", String.class))),
new TextConstant("initialize"),
ArrayFactory.forType(new TypeDescription.Generic.OfNonGenericType.ForLoadedType(Class.class))
.withValues(Arrays.asList(
ClassConstant.of(TypeDescription.CLASS),
ClassConstant.of(new TypeDescription.ForLoadedType(int.class)))),
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(Class.class.getMethod("getMethod", String.class, Class[].class))),
NullConstant.INSTANCE,
ArrayFactory.forType(TypeDescription.Generic.OBJECT)
.withValues(Arrays.asList(
ClassConstant.of(instrumentedMethod.getDeclaringType().asErasure()),
new StackManipulation.Compound(
IntegerConstant.forValue(identification),
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(Integer.class.getMethod("valueOf", int.class)))))),
MethodInvocation.invoke(new MethodDescription.ForLoadedMethod(Method.class.getMethod("invoke", Object.class, Object[].class))),
Removal.SINGLE
)).apply(methodVisitor, implementationContext, instrumentedMethod);
} catch (NoSuchMethodException exception) {
throw new IllegalStateException("Cannot locate method", exception);
}
}
}
/**
* A dispatcher for registering type initializers in the {@link Nexus}.
*/
protected interface Dispatcher {
/**
* Returns {@code true} if this dispatcher is alive.
*
* @return {@code true} if this dispatcher is alive.
*/
boolean isAlive();
/**
* Cleans any dead entries of the system class loader's {@link Nexus}.
*
* @param reference The reference to remove.
*/
void clean(Reference<? extends ClassLoader> reference);
/**
* Registers a type initializer with the system class loader's nexus.
*
* @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 A reference queue to notify about stale nexus entries or {@code null} if no queue should be referenced.
* @param identification An identification for the initializer to run.
* @param loadedTypeInitializer The loaded type initializer to be registered.
*/
void register(String name,
ClassLoader classLoader,
ReferenceQueue<? super ClassLoader> referenceQueue,
int identification,
LoadedTypeInitializer loadedTypeInitializer);
/**
* Creates a new dispatcher for accessing a {@link Nexus}.
*/
enum CreationAction implements PrivilegedAction<Dispatcher> {
/**
* The singleton instance.
*/
INSTANCE;
@Override
@SuppressFBWarnings(value = "REC_CATCH_EXCEPTION", justification = "Exception should not be rethrown but trigger a fallback")
public Dispatcher run() {
if (Boolean.getBoolean(Nexus.PROPERTY)) {
return new Unavailable(new IllegalStateException("Nexus injection was explicitly disabled"));
} else {
try {
Class<?> nexusType = new ClassInjector.UsingReflection(ClassLoader.getSystemClassLoader(), ClassLoadingStrategy.NO_PROTECTION_DOMAIN)
.inject(Collections.singletonMap(new TypeDescription.ForLoadedType(Nexus.class), ClassFileLocator.ForClassLoader.read(Nexus.class).resolve()))
.get(new TypeDescription.ForLoadedType(Nexus.class));
return new Dispatcher.Available(nexusType.getMethod("register", String.class, ClassLoader.class, ReferenceQueue.class, int.class, Object.class),
nexusType.getMethod("clean", Reference.class));
} catch (Exception exception) {
try {
Class<?> nexusType = ClassLoader.getSystemClassLoader().loadClass(Nexus.class.getName());
return new Dispatcher.Available(nexusType.getMethod("register", String.class, ClassLoader.class, ReferenceQueue.class, int.class, Object.class),
nexusType.getMethod("clean", Reference.class));
} catch (Exception ignored) {
return new Dispatcher.Unavailable(exception);
}
}
}
}
}
/**
* An enabled dispatcher for registering a type initializer in a {@link Nexus}.
*/
@EqualsAndHashCode
class Available implements Dispatcher {
/**
* Indicates that a static method is invoked by reflection.
*/
private static final Object STATIC_METHOD = null;
/**
* The {@link Nexus#register(String, ClassLoader, ReferenceQueue, int, Object)} method.
*/
private final Method register;
/**
* The {@link Nexus#clean(Reference)} method.
*/
private final Method clean;
/**
* Creates a new dispatcher.
*
* @param register The {@link Nexus#register(String, ClassLoader, ReferenceQueue, int, Object)} method.
* @param clean The {@link Nexus#clean(Reference)} method.
*/
protected Available(Method register, Method clean) {
this.register = register;
this.clean = clean;
}
@Override
public boolean isAlive() {
return true;
}
@Override
public void clean(Reference<? extends ClassLoader> reference) {
try {
clean.invoke(STATIC_METHOD, reference);
} catch (IllegalAccessException exception) {
throw new IllegalStateException("Cannot access: " + clean, exception);
} catch (InvocationTargetException exception) {
throw new IllegalStateException("Cannot invoke: " + clean, exception.getCause());
}
}
@Override
public void register(String name,
ClassLoader classLoader,
ReferenceQueue<? super ClassLoader> referenceQueue,
int identification,
LoadedTypeInitializer loadedTypeInitializer) {
try {
register.invoke(STATIC_METHOD, name, classLoader, referenceQueue, identification, loadedTypeInitializer);
} catch (IllegalAccessException exception) {
throw new IllegalStateException("Cannot access: " + register, exception);
} catch (InvocationTargetException exception) {
throw new IllegalStateException("Cannot invoke: " + register, exception.getCause());
}
}
}
/**
* A disabled dispatcher where a {@link Nexus} is not available.
*/
@EqualsAndHashCode
class Unavailable implements Dispatcher {
/**
* The exception that was raised during the dispatcher initialization.
*/
private final Exception exception;
/**
* Creates a new disabled dispatcher.
*
* @param exception The exception that was raised during the dispatcher initialization.
*/
protected Unavailable(Exception exception) {
this.exception = exception;
}
@Override
public boolean isAlive() {
return false;
}
@Override
public void clean(Reference<? extends ClassLoader> reference) {
throw new IllegalStateException("Could not initialize Nexus accessor", exception);
}
@Override
public void register(String name,
ClassLoader classLoader,
ReferenceQueue<? super ClassLoader> referenceQueue,
int identification,
LoadedTypeInitializer loadedTypeInitializer) {
throw new IllegalStateException("Could not initialize Nexus accessor", exception);
}
}
}
}