/*
 * 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 android.os;

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.
/**
 * Class that implements the condition variable locking paradigm.
 *
 * <p>
 * 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.
 *
 * <p>
 * This class uses itself as the object to wait on, so if you wait()
 * or notify() on a ConditionVariable, the results are undefined.
 */
public class ConditionVariable
{
    private volatile boolean mCondition;

    
Create the ConditionVariable in the default closed state.
/**
     * 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.
/**
     * Create the ConditionVariable with the given state.
     * 
     * <p>
     * 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.
/**
     * Open the condition, and release all threads that are blocked.
     *
     * <p>
     * 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.
/**
     * Reset the condition to the closed state.
     *
     * <p>
     * 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.
/**
     * Block the current thread until the condition is opened.
     *
     * <p>
     * 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.
Params:
timeout – the maximum time to wait in milliseconds.
Returns:
true if the condition was opened, false if the call returns
because of the timeout./**
     * Block the current thread until the condition is opened or until
     * timeout milliseconds have passed.
     *
     * <p>
     * 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;
        }
    }
}