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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2015 DiffPlug.
 *
 * 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
 *
 * http://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 com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.concurrent.Callable;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Supplier;

/**
 * Static utility methods pertaining to the {@link Callable} interface.
 *
 * @author Isaac Shum
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Callables {
	private Callables() {}

	/**
	 * Creates a {@code Callable} which immediately returns a preset value each
	 * time it is called.
	 */
	public static  Callable returning(final @Nullable T value) {
		return new Callable() {
			@Override
			public T call() {
				return value;
			}
		};
	}

	/**
	 * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
	 * running will have the given name.
	 *
	 *
	 * @param callable The callable to wrap
	 * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
	 *     for each invocation of the wrapped callable.
	 */
	@GwtIncompatible("threads")
	static  Callable threadRenaming(final Callable callable,
			final Supplier nameSupplier) {
		checkNotNull(nameSupplier);
		checkNotNull(callable);
		return new Callable() {
			@Override
			public T call() throws Exception {
				Thread currentThread = Thread.currentThread();
				String oldName = currentThread.getName();
				boolean restoreName = trySetName(nameSupplier.get(), currentThread);
				try {
					return callable.call();
				} finally {
					if (restoreName) {
						trySetName(oldName, currentThread);
					}
				}
			}
		};
	}

	/**
	 * Wraps the given runnable such that for the duration of {@link Runnable#run} the thread that is
	 * running with have the given name.
	 *
	 *
	 * @param task The Runnable to wrap
	 * @param nameSupplier The supplier of thread names, {@link Supplier#get get} will be called once
	 *     for each invocation of the wrapped callable.
	 */
	@GwtIncompatible("threads")
	static Runnable threadRenaming(final Runnable task, final Supplier nameSupplier) {
		checkNotNull(nameSupplier);
		checkNotNull(task);
		return new Runnable() {
			@Override
			public void run() {
				Thread currentThread = Thread.currentThread();
				String oldName = currentThread.getName();
				boolean restoreName = trySetName(nameSupplier.get(), currentThread);
				try {
					task.run();
				} finally {
					if (restoreName) {
						trySetName(oldName, currentThread);
					}
				}
			}
		};
	}

	/** Tries to set name of the given {@link Thread}, returns true if successful. */
	@GwtIncompatible("threads")
	private static boolean trySetName(final String threadName, Thread currentThread) {
		// In AppEngine this will always fail, should we test for that explicitly using
		// MoreExecutors.isAppEngine.  More generally, is there a way to see if we have the modifyThread
		// permission without catching an exception?
		try {
			currentThread.setName(threadName);
			return true;
		} catch (SecurityException e) {
			return false;
		}
	}
}