com.chimerapps.niddler.util.ConditionVariable Maven / Gradle / Ivy

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/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * 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.chimerapps.niddler.util;

import androidx.annotation.RestrictTo;

/**
 * Class that implements the condition variable locking paradigm.
 * 
 * 

 * This differs from the built-in java.lang.Object wait() and notify()
 * in that this class contains the condition to wait on itself.  That means
 * open(), close() and block() are sticky.  If open() is called before block(),
 * block() will not block, and instead return immediately.
 * 

 * 

 * This class uses itself as the object to wait on, so if you wait()
 * or notify() on a ConditionVariable, the results are undefined.
 */
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
public class ConditionVariable {
	private volatile boolean mCondition;

	/**
	 * Create the ConditionVariable in the default closed state.
	 */
	public ConditionVariable() {
		mCondition = false;
	}

	/**
	 * Create the ConditionVariable with the given state.
	 * 

	 * 

	 * Pass true for opened and false for closed.
	 */
	public ConditionVariable(boolean state) {
		mCondition = state;
	}

	/**
	 * Open the condition, and release all threads that are blocked.
	 * 

	 * 

	 * Any threads that later approach block() will not block unless close()
	 * is called.
	 */
	public void open() {
		synchronized (this) {
			boolean old = mCondition;
			mCondition = true;
			if (!old) {
				this.notifyAll();
			}
		}
	}

	/**
	 * Reset the condition to the closed state.
	 * 

	 * 

	 * Any threads that call block() will block until someone calls open.
	 */
	public void close() {
		synchronized (this) {
			mCondition = false;
		}
	}

	/**
	 * Block the current thread until the condition is opened.
	 * 

	 * 

	 * If the condition is already opened, return immediately.
	 */
	public void block() {
		synchronized (this) {
			while (!mCondition) {
				try {
					this.wait();
				} catch (InterruptedException e) {
				}
			}
		}
	}

	/**
	 * Block the current thread until the condition is opened or until
	 * timeout milliseconds have passed.
	 * 

	 * 
	 * If the condition is already opened, return immediately.
	 *
	 * @param timeout the maximum time to wait in milliseconds.
	 * @return true if the condition was opened, false if the call returns
	 * because of the timeout.
	 */
	public boolean block(long timeout) {
		// Object.wait(0) means wait forever, to mimic this, we just
		// call the other block() method in that case.  It simplifies
		// this code for the common case.
		if (timeout != 0) {
			synchronized (this) {
				long now = System.currentTimeMillis();
				long end = now + timeout;
				while (!mCondition && now < end) {
					try {
						this.wait(end - now);
					} catch (InterruptedException e) {
					}
					now = System.currentTimeMillis();
				}
				return mCondition;
			}
		} else {
			this.block();
			return true;
		}
	}
}