/*
 * Copyright 2012-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.boot.devtools.restart;

import java.beans.Introspector;
import java.lang.Thread.UncaughtExceptionHandler;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.Callable;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.CachedIntrospectionResults;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.devtools.restart.FailureHandler.Outcome;
import org.springframework.boot.devtools.restart.classloader.ClassLoaderFiles;
import org.springframework.boot.devtools.restart.classloader.RestartClassLoader;
import org.springframework.boot.logging.DeferredLog;
import org.springframework.boot.system.JavaVersion;
import org.springframework.cglib.core.ClassNameReader;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.core.ResolvableType;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.core.io.ResourceLoader;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;

Allows a running application to be restarted with an updated classpath. The restarter
works by creating a new application ClassLoader that is split into two parts. The top
part contains static URLs that don't change (for example 3rd party libraries and Spring
Boot itself) and the bottom part contains URLs where classes and resources might be
updated.
 The Restarter should be initialized early to ensure that classes are loaded multiple times. Mostly the RestartApplicationListener can be relied upon to perform initialization, however, you may need to call initialize(String[]) directly if your SpringApplication arguments are not identical to your main method arguments. 

By default, applications running in an IDE (i.e. those not packaged as "fat jars") will
automatically detect URLs that can change. It's also possible to manually configure
URLs or class file updates for remote restart scenarios.
Author:
Phillip Webb, Andy Wilkinson
See Also:
RestartApplicationListener
initialize(String[])
getInstance()
restart()
Since:
1.3.0/**
 * Allows a running application to be restarted with an updated classpath. The restarter
 * works by creating a new application ClassLoader that is split into two parts. The top
 * part contains static URLs that don't change (for example 3rd party libraries and Spring
 * Boot itself) and the bottom part contains URLs where classes and resources might be
 * updated.
 * <p>
 * The Restarter should be {@link #initialize(String[]) initialized} early to ensure that
 * classes are loaded multiple times. Mostly the {@link RestartApplicationListener} can be
 * relied upon to perform initialization, however, you may need to call
 * {@link #initialize(String[])} directly if your SpringApplication arguments are not
 * identical to your main method arguments.
 * <p>
 * By default, applications running in an IDE (i.e. those not packaged as "fat jars") will
 * automatically detect URLs that can change. It's also possible to manually configure
 * URLs or class file updates for remote restart scenarios.
 *
 * @author Phillip Webb
 * @author Andy Wilkinson
 * @since 1.3.0
 * @see RestartApplicationListener
 * @see #initialize(String[])
 * @see #getInstance()
 * @see #restart()
 */
public class Restarter {

	private static final Object INSTANCE_MONITOR = new Object();

	private static final String[] NO_ARGS = {};

	private static Restarter instance;

	private final Set<URL> urls = new LinkedHashSet<>();

	private final ClassLoaderFiles classLoaderFiles = new ClassLoaderFiles();

	private final Map<String, Object> attributes = new HashMap<>();

	private final BlockingDeque<LeakSafeThread> leakSafeThreads = new LinkedBlockingDeque<>();

	private final Lock stopLock = new ReentrantLock();

	private final Object monitor = new Object();

	private Log logger = new DeferredLog();

	private final boolean forceReferenceCleanup;

	private boolean enabled = true;

	private URL[] initialUrls;

	private final String mainClassName;

	private final ClassLoader applicationClassLoader;

	private final String[] args;

	private final UncaughtExceptionHandler exceptionHandler;

	private boolean finished = false;

	private final List<ConfigurableApplicationContext> rootContexts = new CopyOnWriteArrayList<>();

	
Internal constructor to create a new Restarter instance. 
Params:
thread – the source thread
args – the application arguments
forceReferenceCleanup – if soft/weak reference cleanup should be forced
initializer – the restart initializer
See Also:
initialize(String[])/**
	 * Internal constructor to create a new {@link Restarter} instance.
	 * @param thread the source thread
	 * @param args the application arguments
	 * @param forceReferenceCleanup if soft/weak reference cleanup should be forced
	 * @param initializer the restart initializer
	 * @see #initialize(String[])
	 */
	protected Restarter(Thread thread, String[] args, boolean forceReferenceCleanup, RestartInitializer initializer) {
		Assert.notNull(thread, "Thread must not be null");
		Assert.notNull(args, "Args must not be null");
		Assert.notNull(initializer, "Initializer must not be null");
		if (this.logger.isDebugEnabled()) {
			this.logger.debug("Creating new Restarter for thread " + thread);
		}
		SilentExitExceptionHandler.setup(thread);
		this.forceReferenceCleanup = forceReferenceCleanup;
		this.initialUrls = initializer.getInitialUrls(thread);
		this.mainClassName = getMainClassName(thread);
		this.applicationClassLoader = thread.getContextClassLoader();
		this.args = args;
		this.exceptionHandler = thread.getUncaughtExceptionHandler();
		this.leakSafeThreads.add(new LeakSafeThread());
	}

	private String getMainClassName(Thread thread) {
		try {
			return new MainMethod(thread).getDeclaringClassName();
		}
		catch (Exception ex) {
			return null;
		}
	}

	protected void initialize(boolean restartOnInitialize) {
		preInitializeLeakyClasses();
		if (this.initialUrls != null) {
			this.urls.addAll(Arrays.asList(this.initialUrls));
			if (restartOnInitialize) {
				this.logger.debug("Immediately restarting application");
				immediateRestart();
			}
		}
	}

	private void immediateRestart() {
		try {
			getLeakSafeThread().callAndWait(() -> {
				start(FailureHandler.NONE);
				cleanupCaches();
				return null;
			});
		}
		catch (Exception ex) {
			this.logger.warn("Unable to initialize restarter", ex);
		}
		SilentExitExceptionHandler.exitCurrentThread();
	}

	
CGLIB has a private exception field which needs to initialized early to ensure that
the stacktrace doesn't retain a reference to the RestartClassLoader.
/**
	 * CGLIB has a private exception field which needs to initialized early to ensure that
	 * the stacktrace doesn't retain a reference to the RestartClassLoader.
	 */
	private void preInitializeLeakyClasses() {
		try {
			Class<?> readerClass = ClassNameReader.class;
			Field field = readerClass.getDeclaredField("EARLY_EXIT");
			field.setAccessible(true);
			((Throwable) field.get(null)).fillInStackTrace();
		}
		catch (Exception ex) {
			this.logger.warn("Unable to pre-initialize classes", ex);
		}
	}

	
Set if restart support is enabled.
Params:
enabled – if restart support is enabled/**
	 * Set if restart support is enabled.
	 * @param enabled if restart support is enabled
	 */
	private void setEnabled(boolean enabled) {
		this.enabled = enabled;
	}

	
Add additional URLs to be includes in the next restart.
Params:
urls – the urls to add/**
	 * Add additional URLs to be includes in the next restart.
	 * @param urls the urls to add
	 */
	public void addUrls(Collection<URL> urls) {
		Assert.notNull(urls, "Urls must not be null");
		this.urls.addAll(urls);
	}

	
Add additional ClassLoaderFiles to be included in the next restart. 
Params:
classLoaderFiles – the files to add/**
	 * Add additional {@link ClassLoaderFiles} to be included in the next restart.
	 * @param classLoaderFiles the files to add
	 */
	public void addClassLoaderFiles(ClassLoaderFiles classLoaderFiles) {
		Assert.notNull(classLoaderFiles, "ClassLoaderFiles must not be null");
		this.classLoaderFiles.addAll(classLoaderFiles);
	}

	
Return a ThreadFactory that can be used to create leak safe threads. 
Returns:
a leak safe thread factory/**
	 * Return a {@link ThreadFactory} that can be used to create leak safe threads.
	 * @return a leak safe thread factory
	 */
	public ThreadFactory getThreadFactory() {
		return new LeakSafeThreadFactory();
	}

	
Restart the running application.
/**
	 * Restart the running application.
	 */
	public void restart() {
		restart(FailureHandler.NONE);
	}

	
Restart the running application.
Params:
failureHandler – a failure handler to deal with application that doesn't start/**
	 * Restart the running application.
	 * @param failureHandler a failure handler to deal with application that doesn't start
	 */
	public void restart(FailureHandler failureHandler) {
		if (!this.enabled) {
			this.logger.debug("Application restart is disabled");
			return;
		}
		this.logger.debug("Restarting application");
		getLeakSafeThread().call(() -> {
			Restarter.this.stop();
			Restarter.this.start(failureHandler);
			return null;
		});
	}

	
Start the application.
Params:
failureHandler – a failure handler for application that won't start
Throws:
Exception – in case of errors/**
	 * Start the application.
	 * @param failureHandler a failure handler for application that won't start
	 * @throws Exception in case of errors
	 */
	protected void start(FailureHandler failureHandler) throws Exception {
		do {
			Throwable error = doStart();
			if (error == null) {
				return;
			}
			if (failureHandler.handle(error) == Outcome.ABORT) {
				return;
			}
		}
		while (true);
	}

	private Throwable doStart() throws Exception {
		Assert.notNull(this.mainClassName, "Unable to find the main class to restart");
		URL[] urls = this.urls.toArray(new URL[0]);
		ClassLoaderFiles updatedFiles = new ClassLoaderFiles(this.classLoaderFiles);
		ClassLoader classLoader = new RestartClassLoader(this.applicationClassLoader, urls, updatedFiles, this.logger);
		if (this.logger.isDebugEnabled()) {
			this.logger.debug("Starting application " + this.mainClassName + " with URLs " + Arrays.asList(urls));
		}
		return relaunch(classLoader);
	}

	
Relaunch the application using the specified classloader.
Params:
classLoader – the classloader to use
Throws:
Exception – in case of errors
Returns:
any exception that caused the launch to fail or null/**
	 * Relaunch the application using the specified classloader.
	 * @param classLoader the classloader to use
	 * @return any exception that caused the launch to fail or {@code null}
	 * @throws Exception in case of errors
	 */
	protected Throwable relaunch(ClassLoader classLoader) throws Exception {
		RestartLauncher launcher = new RestartLauncher(classLoader, this.mainClassName, this.args,
				this.exceptionHandler);
		launcher.start();
		launcher.join();
		return launcher.getError();
	}

	
Stop the application.
Throws:
Exception – in case of errors/**
	 * Stop the application.
	 * @throws Exception in case of errors
	 */
	protected void stop() throws Exception {
		this.logger.debug("Stopping application");
		this.stopLock.lock();
		try {
			for (ConfigurableApplicationContext context : this.rootContexts) {
				context.close();
				this.rootContexts.remove(context);
			}
			cleanupCaches();
			if (this.forceReferenceCleanup) {
				forceReferenceCleanup();
			}
		}
		finally {
			this.stopLock.unlock();
		}
		System.gc();
		System.runFinalization();
	}

	private void cleanupCaches() throws Exception {
		Introspector.flushCaches();
		cleanupKnownCaches();
	}

	private void cleanupKnownCaches() throws Exception {
		// Whilst not strictly necessary it helps to cleanup soft reference caches
		// early rather than waiting for memory limits to be reached
		ResolvableType.clearCache();
		cleanCachedIntrospectionResultsCache();
		ReflectionUtils.clearCache();
		clearAnnotationUtilsCache();
		if (!JavaVersion.getJavaVersion().isEqualOrNewerThan(JavaVersion.NINE)) {
			clear("com.sun.naming.internal.ResourceManager", "propertiesCache");
		}
	}

	private void cleanCachedIntrospectionResultsCache() throws Exception {
		clear(CachedIntrospectionResults.class, "acceptedClassLoaders");
		clear(CachedIntrospectionResults.class, "strongClassCache");
		clear(CachedIntrospectionResults.class, "softClassCache");
	}

	private void clearAnnotationUtilsCache() throws Exception {
		try {
			AnnotationUtils.clearCache();
		}
		catch (Throwable ex) {
			clear(AnnotationUtils.class, "findAnnotationCache");
			clear(AnnotationUtils.class, "annotatedInterfaceCache");
		}
	}

	private void clear(String className, String fieldName) {
		try {
			clear(Class.forName(className), fieldName);
		}
		catch (Exception ex) {
			if (this.logger.isDebugEnabled()) {
				this.logger.debug("Unable to clear field " + className + " " + fieldName, ex);
			}
		}
	}

	private void clear(Class<?> type, String fieldName) throws Exception {
		try {
			Field field = type.getDeclaredField(fieldName);
			field.setAccessible(true);
			Object instance = field.get(null);
			if (instance instanceof Set) {
				((Set<?>) instance).clear();
			}
			if (instance instanceof Map) {
				((Map<?, ?>) instance).keySet().removeIf(this::isFromRestartClassLoader);
			}
		}
		catch (Exception ex) {
			if (this.logger.isDebugEnabled()) {
				this.logger.debug("Unable to clear field " + type + " " + fieldName, ex);
			}
		}
	}

	private boolean isFromRestartClassLoader(Object object) {
		return (object instanceof Class && ((Class<?>) object).getClassLoader() instanceof RestartClassLoader);
	}

	
Cleanup any soft/weak references by forcing an OutOfMemoryError error. /**
	 * Cleanup any soft/weak references by forcing an {@link OutOfMemoryError} error.
	 */
	private void forceReferenceCleanup() {
		try {
			final List<long[]> memory = new LinkedList<>();
			while (true) {
				memory.add(new long[102400]);
			}
		}
		catch (OutOfMemoryError ex) {
			// Expected
		}
	}

	
Called to finish Restarter initialization when application logging is available. /**
	 * Called to finish {@link Restarter} initialization when application logging is
	 * available.
	 */
	void finish() {
		synchronized (this.monitor) {
			if (!isFinished()) {
				this.logger = DeferredLog.replay(this.logger, LogFactory.getLog(getClass()));
				this.finished = true;
			}
		}
	}

	boolean isFinished() {
		synchronized (this.monitor) {
			return this.finished;
		}
	}

	void prepare(ConfigurableApplicationContext applicationContext) {
		if (applicationContext != null && applicationContext.getParent() != null) {
			return;
		}
		if (applicationContext instanceof GenericApplicationContext) {
			prepare((GenericApplicationContext) applicationContext);
		}
		this.rootContexts.add(applicationContext);
	}

	void remove(ConfigurableApplicationContext applicationContext) {
		if (applicationContext != null) {
			this.rootContexts.remove(applicationContext);
		}
	}

	private void prepare(GenericApplicationContext applicationContext) {
		ResourceLoader resourceLoader = new ClassLoaderFilesResourcePatternResolver(applicationContext,
				this.classLoaderFiles);
		applicationContext.setResourceLoader(resourceLoader);
	}

	private LeakSafeThread getLeakSafeThread() {
		try {
			return this.leakSafeThreads.takeFirst();
		}
		catch (InterruptedException ex) {
			Thread.currentThread().interrupt();
			throw new IllegalStateException(ex);
		}
	}

	public Object getOrAddAttribute(String name, final ObjectFactory<?> objectFactory) {
		synchronized (this.attributes) {
			if (!this.attributes.containsKey(name)) {
				this.attributes.put(name, objectFactory.getObject());
			}
			return this.attributes.get(name);
		}
	}

	public Object removeAttribute(String name) {
		synchronized (this.attributes) {
			return this.attributes.remove(name);
		}
	}

	
Return the initial set of URLs as configured by the RestartInitializer. 
Returns:
the initial URLs or null/**
	 * Return the initial set of URLs as configured by the {@link RestartInitializer}.
	 * @return the initial URLs or {@code null}
	 */
	public URL[] getInitialUrls() {
		return this.initialUrls;
	}

	
Initialize and disable restart support.
/**
	 * Initialize and disable restart support.
	 */
	public static void disable() {
		initialize(NO_ARGS, false, RestartInitializer.NONE);
		getInstance().setEnabled(false);
	}

	
Initialize restart support. See initialize(String[], boolean, RestartInitializer) for details. 
Params:
args – main application arguments
See Also:
initialize(String[], boolean, RestartInitializer)/**
	 * Initialize restart support. See
	 * {@link #initialize(String[], boolean, RestartInitializer)} for details.
	 * @param args main application arguments
	 * @see #initialize(String[], boolean, RestartInitializer)
	 */
	public static void initialize(String[] args) {
		initialize(args, false, new DefaultRestartInitializer());
	}

	
Initialize restart support. See initialize(String[], boolean, RestartInitializer) for details. 
Params:
args – main application arguments
initializer – the restart initializer
See Also:
initialize(String[], boolean, RestartInitializer)/**
	 * Initialize restart support. See
	 * {@link #initialize(String[], boolean, RestartInitializer)} for details.
	 * @param args main application arguments
	 * @param initializer the restart initializer
	 * @see #initialize(String[], boolean, RestartInitializer)
	 */
	public static void initialize(String[] args, RestartInitializer initializer) {
		initialize(args, false, initializer, true);
	}

	
Initialize restart support. See initialize(String[], boolean, RestartInitializer) for details. 
Params:
args – main application arguments
forceReferenceCleanup – if forcing of soft/weak reference should happen on
See Also:
initialize(String[], boolean, RestartInitializer)/**
	 * Initialize restart support. See
	 * {@link #initialize(String[], boolean, RestartInitializer)} for details.
	 * @param args main application arguments
	 * @param forceReferenceCleanup if forcing of soft/weak reference should happen on
	 * @see #initialize(String[], boolean, RestartInitializer)
	 */
	public static void initialize(String[] args, boolean forceReferenceCleanup) {
		initialize(args, forceReferenceCleanup, new DefaultRestartInitializer());
	}

	
Initialize restart support. See initialize(String[], boolean, RestartInitializer, boolean) for details. 
Params:
args – main application arguments
forceReferenceCleanup – if forcing of soft/weak reference should happen on
initializer – the restart initializer
See Also:
initialize(String[], boolean, RestartInitializer)/**
	 * Initialize restart support. See
	 * {@link #initialize(String[], boolean, RestartInitializer, boolean)} for details.
	 * @param args main application arguments
	 * @param forceReferenceCleanup if forcing of soft/weak reference should happen on
	 * @param initializer the restart initializer
	 * @see #initialize(String[], boolean, RestartInitializer)
	 */
	public static void initialize(String[] args, boolean forceReferenceCleanup, RestartInitializer initializer) {
		initialize(args, forceReferenceCleanup, initializer, true);
	}

	
Initialize restart support for the current application. Called automatically by RestartApplicationListener but can also be called directly if main application arguments are not the same as those passed to the SpringApplication. 
Params:
args – main application arguments
forceReferenceCleanup – if forcing of soft/weak reference should happen on
each restart. This will slow down restarts and is intended primarily for testing
initializer – the restart initializer
restartOnInitialize – if the restarter should be restarted immediately when the RestartInitializer returns non null results/**
	 * Initialize restart support for the current application. Called automatically by
	 * {@link RestartApplicationListener} but can also be called directly if main
	 * application arguments are not the same as those passed to the
	 * {@link SpringApplication}.
	 * @param args main application arguments
	 * @param forceReferenceCleanup if forcing of soft/weak reference should happen on
	 * each restart. This will slow down restarts and is intended primarily for testing
	 * @param initializer the restart initializer
	 * @param restartOnInitialize if the restarter should be restarted immediately when
	 * the {@link RestartInitializer} returns non {@code null} results
	 */
	public static void initialize(String[] args, boolean forceReferenceCleanup, RestartInitializer initializer,
			boolean restartOnInitialize) {
		Restarter localInstance = null;
		synchronized (INSTANCE_MONITOR) {
			if (instance == null) {
				localInstance = new Restarter(Thread.currentThread(), args, forceReferenceCleanup, initializer);
				instance = localInstance;
			}
		}
		if (localInstance != null) {
			localInstance.initialize(restartOnInitialize);
		}
	}

	
Return the active Restarter instance. Cannot be called before initialization. 
Returns:
the restarter/**
	 * Return the active {@link Restarter} instance. Cannot be called before
	 * {@link #initialize(String[]) initialization}.
	 * @return the restarter
	 */
	public static Restarter getInstance() {
		synchronized (INSTANCE_MONITOR) {
			Assert.state(instance != null, "Restarter has not been initialized");
			return instance;
		}
	}

	
Set the restarter instance (useful for testing).
Params:
instance – the instance to set/**
	 * Set the restarter instance (useful for testing).
	 * @param instance the instance to set
	 */
	static void setInstance(Restarter instance) {
		synchronized (INSTANCE_MONITOR) {
			Restarter.instance = instance;
		}
	}

	
Clear the instance. Primarily provided for tests and not usually used in
application code.
/**
	 * Clear the instance. Primarily provided for tests and not usually used in
	 * application code.
	 */
	public static void clearInstance() {
		synchronized (INSTANCE_MONITOR) {
			instance = null;
		}
	}

	
Thread that is created early so not to retain the RestartClassLoader. /**
	 * Thread that is created early so not to retain the {@link RestartClassLoader}.
	 */
	private class LeakSafeThread extends Thread {

		private Callable<?> callable;

		private Object result;

		LeakSafeThread() {
			setDaemon(false);
		}

		void call(Callable<?> callable) {
			this.callable = callable;
			start();
		}

		@SuppressWarnings("unchecked")
		<V> V callAndWait(Callable<V> callable) {
			this.callable = callable;
			start();
			try {
				join();
				return (V) this.result;
			}
			catch (InterruptedException ex) {
				Thread.currentThread().interrupt();
				throw new IllegalStateException(ex);
			}
		}

		@Override
		public void run() {
			// We are safe to refresh the ActionThread (and indirectly call
			// AccessController.getContext()) since our stack doesn't include the
			// RestartClassLoader
			try {
				Restarter.this.leakSafeThreads.put(new LeakSafeThread());
				this.result = this.callable.call();
			}
			catch (Exception ex) {
				ex.printStackTrace();
				System.exit(1);
			}
		}

	}

	
ThreadFactory that creates a leak safe thread. /**
	 * {@link ThreadFactory} that creates a leak safe thread.
	 */
	private class LeakSafeThreadFactory implements ThreadFactory {

		@Override
		public Thread newThread(Runnable runnable) {
			return getLeakSafeThread().callAndWait(() -> {
				Thread thread = new Thread(runnable);
				thread.setContextClassLoader(Restarter.this.applicationClassLoader);
				return thread;
			});
		}

	}

}