/*
* @(#)$Id: codetemplate_xbird.xml 943 2006-09-13 07:03:37Z yui $
*
* Copyright 2006-2008 Makoto YUI
*
* 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.
*
* Contributors:
* Makoto YUI - initial implementation
*/
package xbird.util.concurrent.lock;
import java.util.concurrent.atomic.AtomicBoolean;
/**
*
* <DIV lang="en"></DIV>
* <DIV lang="ja"></DIV>
*
* @author Makoto YUI (yuin405+xbird@gmail.com)
*/
public final class AtomicBackoffLock implements ILock {
private final int _spinsBeforeYield;
private final int _spinsBeforeSleep;
private final long _initSleepTime;
private final AtomicBoolean state;
public AtomicBackoffLock() {
this(128, 256, 1, false);
}
public AtomicBackoffLock(boolean lock) {
this(128, 256, 1, lock);
}
public AtomicBackoffLock(int spinsInterval) {
this(spinsInterval, spinsInterval << 1, 1, false);
}
public AtomicBackoffLock(int spinsInterval, boolean lock) {
this(spinsInterval, spinsInterval << 1, 1, lock);
}
public AtomicBackoffLock(int spinsBeforeYield, int spinsBeforeSleep, long initSleepTime, boolean lock) {
this._spinsBeforeSleep = spinsBeforeSleep;
this._spinsBeforeYield = spinsBeforeYield;
this._initSleepTime = initSleepTime;
this.state = new AtomicBoolean(lock);
}
public boolean isLocked() {
return state.get();
}
public void lock() {
final int spinsBeforeYield = _spinsBeforeYield;
final int spinsBeforeSleep = _spinsBeforeSleep;
long sleepTime = _initSleepTime;
int spins = 0;
while(true) {
if(!state.get()) { // test-and-test-and-set
if(!state.getAndSet(true)) {
return;
}
}
if(spins < spinsBeforeYield) { // spin phase
++spins;
} else if(spins < spinsBeforeSleep) { // yield phase
++spins;
Thread.yield();
} else { // back-off phase
try {
Thread.sleep(sleepTime);
} catch (InterruptedException e) {
throw new IllegalStateException(e);
}
sleepTime = (3 * sleepTime) >> 1 + 1; // 50% is arbitrary
}
}
}
public boolean tryLock() {
if(!state.get()) {
if(!state.getAndSet(true)) {
return true;
}
}
return false;
}
public void unlock() {
state.set(false);
}
}