// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// 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.cloud.utils.db;
import static java.lang.String.format;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import org.apache.log4j.Logger;
import com.cloud.utils.Profiler;
//
// Wrapper class for global database lock to reduce contention for database connections from within process
//
// Example of using dynamic named locks
//
// GlobalLock lock = GlobalLock.getInternLock("some table name" + rowId);
//
// if(lock.lock()) {
// try {
// do something
// } finally {
// lock.unlock();
// }
// }
// lock.releaseRef();
//
public class GlobalLock {
protected final static Logger s_logger = Logger.getLogger(GlobalLock.class);
private String name;
private int lockCount = 0;
private Thread ownerThread = null;
private int referenceCount = 0;
private long holdingStartTick = 0;
private static Map<String, GlobalLock> s_lockMap = new HashMap<String, GlobalLock>();
private GlobalLock(String name) {
this.name = name;
}
public int addRef() {
synchronized (this) {
referenceCount++;
return referenceCount;
}
}
public int releaseRef() {
int refCount;
boolean needToRemove = false;
synchronized (this) {
referenceCount--;
refCount = referenceCount;
if (referenceCount < 0)
s_logger.warn("Unmatched Global lock " + name + " reference usage detected, check your code!");
if (referenceCount == 0)
needToRemove = true;
}
if (needToRemove)
releaseInternLock(name);
return refCount;
}
public static GlobalLock getInternLock(String name) {
synchronized (s_lockMap) {
if (s_lockMap.containsKey(name)) {
GlobalLock lock = s_lockMap.get(name);
lock.addRef();
return lock;
} else {
GlobalLock lock = new GlobalLock(name);
lock.addRef();
s_lockMap.put(name, lock);
return lock;
}
}
}
private static void releaseInternLock(String name) {
synchronized (s_lockMap) {
GlobalLock lock = s_lockMap.get(name);
if (lock != null) {
if (lock.referenceCount == 0)
s_lockMap.remove(name);
} else {
s_logger.warn("Releasing " + name + ", but it is already released.");
}
}
}
public boolean lock(int timeoutSeconds) {
int remainingMilliSeconds = timeoutSeconds * 1000;
Profiler profiler = new Profiler();
boolean interrupted = false;
try {
while (true) {
synchronized (this) {
if (ownerThread != null && ownerThread == Thread.currentThread()) {
s_logger.warn("Global lock re-entrance detected");
lockCount++;
if (s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is acquired, lock count :" + lockCount);
return true;
}
if (ownerThread != null) {
profiler.start();
try {
wait((timeoutSeconds) * 1000L);
} catch (InterruptedException e) {
interrupted = true;
}
profiler.stop();
remainingMilliSeconds -= profiler.getDurationInMillis();
if (remainingMilliSeconds < 0)
return false;
continue;
} else {
// take ownership temporarily to prevent others enter into stage of acquiring DB lock
ownerThread = Thread.currentThread();
addRef();
}
}
if (DbUtil.getGlobalLock(name, remainingMilliSeconds / 1000)) {
synchronized (this) {
lockCount++;
holdingStartTick = System.currentTimeMillis();
if (s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is acquired, lock count :" + lockCount);
return true;
}
} else {
synchronized (this) {
ownerThread = null;
releaseRef();
return false;
}
}
}
} finally {
if (interrupted) {
Thread.currentThread().interrupt();
}
}
}
public boolean unlock() {
synchronized (this) {
if (ownerThread != null && ownerThread == Thread.currentThread()) {
lockCount--;
if (lockCount == 0) {
ownerThread = null;
DbUtil.releaseGlobalLock(name);
if (s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is returned to free state, total holding time :" + (System.currentTimeMillis() - holdingStartTick));
holdingStartTick = 0;
// release holding position in intern map when we released the DB connection
releaseRef();
notifyAll();
}
if (s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is released, lock count :" + lockCount);
return true;
}
return false;
}
}
public String getName() {
return name;
}
public static <T> T executeWithLock(final String operationId, final int lockAcquisitionTimeout, final Callable<T> operation) throws Exception {
final GlobalLock lock = GlobalLock.getInternLock(operationId);
try {
if (!lock.lock(lockAcquisitionTimeout)) {
if (s_logger.isDebugEnabled()) {
s_logger.debug(format("Failed to acquire lock for operation id %1$s", operationId));
}
return null;
}
return operation.call();
} finally {
if (lock != null) {
lock.unlock();
}
}
}
public static <T> T executeWithNoWaitLock(final String operationId, final Callable<T> operation) throws Exception {
return executeWithLock(operationId, 0, operation);
}
}