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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 android.os;
/**
* 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.
*/
public ConditionVariable()
{
mCondition = false;
}
/**
* 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.
*
* <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.
*
* <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.
*
* <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.
*
* <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;
}
}
}
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