/*
* Copyright (c) 1998-2011 Caucho Technology -- all rights reserved
*
* This file is part of Resin(R) Open Source
*
* Each copy or derived work must preserve the copyright notice and this
* notice unmodified.
*
* Resin Open Source is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* Resin Open Source is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
* of NON-INFRINGEMENT. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License
* along with Resin Open Source; if not, write to the
*
* Free Software Foundation, Inc.
* 59 Temple Place, Suite 330
* Boston, MA 02111-1307 USA
*
* @author Scott Ferguson
*/
package com.caucho.db.lock;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import com.caucho.util.Alarm;
/**
* Locking for tables/etc.
*/
public final class DatabaseLock implements ReadWriteLock {
private final static
AtomicLongFieldUpdater<DatabaseLock> _lockCountUpdater;
private static final long LOCK_WAIT = 1L << 32;
private static final long LOCK_WAIT_MASK = 0xffffffffL << 32;
private static final long LOCK_WRITE = 1L << 31;
private static final long LOCK_WRITE_MASK = 1L << 31;
private static final long LOCK_READ = 1L;
private static final long LOCK_READ_MASK = 0x7fffffffL;
private static final long LOCK_MASK = LOCK_WRITE_MASK | LOCK_READ_MASK;
private static final long LOCK_CAN_READ_MASK = LOCK_WRITE_MASK | LOCK_WAIT_MASK;
private final Lock _readLock = new ReadLockImpl();
private final Lock _writeLock = new WriteLockImpl();
private volatile long _lockCount;
public DatabaseLock(String id)
{
}
@Override
public Lock readLock()
{
return _readLock;
}
@Override
public Lock writeLock()
{
return _writeLock;
}
/**
* Tries to get a read lock.
*
* @param timeout how long to wait for a timeout
*/
/*
public void lockRead(long timeout)
throws LockTimeoutException
{
if (log.isLoggable(Level.FINEST)) {
log.finest(this + " lockRead 0x" + Long.toHexString(_lockCount));
}
long lock;
while (true) {
lock = _lockCount;
if (lock < NODE_LOCK) {
if (_lockCountUpdater.compareAndSet(this, lock, lock + READ)) {
return;
}
}
else {
addReadLock(timeout);
return;
}
}
}
*/
public void lockRead(long timeout)
throws LockTimeoutException
{
if (lockReadCounter())
return;
long expires = Alarm.getCurrentTimeActual() + timeout;
boolean isValid = false;
try {
lockReadWait(expires);
isValid = true;
} finally {
if (! isValid)
unlockWait();
}
}
/**
* Attempts to get an exclusive write lock.
*/
public void lockWrite(long timeout)
{
if (lockWriteCounter())
return;
long expires = Alarm.getCurrentTimeActual() + timeout;
boolean isValid = false;
try {
lockWriteWait(expires);
isValid = true;
} finally {
if (! isValid)
unlockWait();
}
}
public void unlockRead()
{
unlockReadCounter();
}
/**
* Unlocks the write
*/
public void unlockWrite()
{
unlockWriteCounter();
}
private boolean lockReadCounter()
{
long lock;
long newLock;
boolean isQuickLock;
do {
lock = _lockCount;
isQuickLock = isLockCanRead(lock);
if (isQuickLock)
newLock = lock + LOCK_READ;
else
newLock = lock + LOCK_WAIT;
} while (! _lockCountUpdater.compareAndSet(this, lock, newLock));
return isQuickLock;
}
private boolean lockWriteCounter()
{
long lock;
long newLock;
boolean isQuickLock;
do {
lock = _lockCount;
isQuickLock = isLockCanWrite(lock);
if (isQuickLock)
newLock = lock + LOCK_WRITE;
else
newLock = lock + LOCK_WAIT;
} while (! _lockCountUpdater.compareAndSet(this, lock, newLock));
return isQuickLock;
}
private void unlockWait()
{
long lock;
long newLock;
do {
lock = _lockCount;
newLock = lock - LOCK_WAIT;
} while (! _lockCountUpdater.compareAndSet(this, lock, newLock));
}
private void unlockReadCounter()
{
long lock;
long newLock;
boolean isWaiter;
do {
lock = _lockCount;
isWaiter = ((lock & LOCK_WAIT_MASK) != 0);
newLock = lock - LOCK_READ;
} while (! _lockCountUpdater.compareAndSet(this, lock, newLock));
if (isWaiter) {
synchronized (this) {
this.notify();
}
}
}
private void unlockWriteCounter()
{
long lock;
long newLock;
boolean isWaiter;
do {
lock = _lockCount;
isWaiter = ((lock & LOCK_WAIT_MASK) != 0);
newLock = lock - LOCK_WRITE;
} while (! _lockCountUpdater.compareAndSet(this, lock, newLock));
if (isWaiter) {
synchronized (this) {
this.notify();
}
}
}
private void lockReadWait(long expires)
{
synchronized (this) {
while (true) {
long lock;
while (isLockCanRead(lock = _lockCount)) {
long newLock = lock + LOCK_READ - LOCK_WAIT;
if (_lockCountUpdater.compareAndSet(this, lock, newLock)) {
return;
}
}
long delta = expires - Alarm.getCurrentTimeActual();
if (delta <= 0) {
throw new LockTimeoutException();
}
try {
this.wait(delta);
} catch (Exception e) {
}
}
}
}
private void lockWriteWait(long expires)
{
synchronized (this) {
while (true) {
long lock;
while (isLockCanWrite(lock = _lockCount)) {
long newLock = lock + LOCK_WRITE - LOCK_WAIT;
if (_lockCountUpdater.compareAndSet(this, lock, newLock)) {
return;
}
}
long delta = expires - Alarm.getCurrentTimeActual();
if (delta <= 0) {
throw new LockTimeoutException();
}
try {
this.wait(delta);
} catch (Exception e) {
}
}
}
}
private static boolean isLockCanRead(long lock)
{
return (lock & LOCK_CAN_READ_MASK) == 0 || (lock & LOCK_MASK) == 0;
}
private static boolean isLockCanWrite(long lock)
{
return (lock & LOCK_MASK) == 0;
}
@Override
public String toString()
{
return getClass().getSimpleName() + "[]";
}
enum LockType {
READ,
WRITE
};
final class ReadLockImpl implements Lock {
@Override
public final boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException
{
lockRead(unit.toMillis(timeout));
return true;
}
@Override
public final void unlock()
{
unlockRead();
}
@Override
public final void lock()
{
try {
if (! tryLock(Long.MAX_VALUE / 2, TimeUnit.MILLISECONDS)) {
throw new IllegalStateException();
}
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
@Override
public boolean tryLock()
{
try {
return tryLock(Long.MAX_VALUE / 2, TimeUnit.MILLISECONDS);
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
@Override
public void lockInterruptibly() throws InterruptedException
{
throw new UnsupportedOperationException(getClass().getName());
}
@Override
public Condition newCondition()
{
throw new UnsupportedOperationException(getClass().getName());
}
}
class WriteLockImpl implements Lock {
@Override
public boolean tryLock(long time, TimeUnit unit)
throws InterruptedException
{
lockWrite(unit.toMillis(time));
return true;
}
@Override
public void unlock()
{
unlockWrite();
}
@Override
public void lock()
{
try {
if (! tryLock(Long.MAX_VALUE / 2, TimeUnit.MILLISECONDS)) {
throw new IllegalStateException();
}
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
@Override
public boolean tryLock()
{
try {
return tryLock(Long.MAX_VALUE / 2, TimeUnit.MILLISECONDS);
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
@Override
public void lockInterruptibly() throws InterruptedException
{
throw new UnsupportedOperationException(getClass().getName());
}
@Override
public Condition newCondition()
{
throw new UnsupportedOperationException(getClass().getName());
}
}
static {
_lockCountUpdater
= AtomicLongFieldUpdater.newUpdater(DatabaseLock.class, "_lockCount");
}
}