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/**
* 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 with the License.
* You may obtain a copy of the License at
* <p>
* http://www.apache.org/licenses/LICENSE-2.0
* <p>
* 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 org.apache.hadoop.ozone.lock;
import org.apache.commons.pool2.impl.GenericObjectPool;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hdds.HddsConfigKeys;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/**
* Manages the locks on a given resource. A new lock is created for each
* and every unique resource. Uniqueness of resource depends on the
* {@code equals} implementation of it.
*/
public class LockManager<T> {
private static final Logger LOG = LoggerFactory.getLogger(LockManager.class);
private final Map<T, ActiveLock> activeLocks = new ConcurrentHashMap<>();
private final GenericObjectPool<ActiveLock> lockPool =
new GenericObjectPool<>(new PooledLockFactory());
/**
* Creates new LockManager instance.
*
* @param conf Configuration object
*/
public LockManager(Configuration conf) {
int maxPoolSize = conf.getInt(HddsConfigKeys.HDDS_LOCK_MAX_CONCURRENCY,
HddsConfigKeys.HDDS_LOCK_MAX_CONCURRENCY_DEFAULT);
lockPool.setMaxTotal(maxPoolSize);
}
/**
* Acquires the lock on given resource.
*
* <p>If the lock is not available then the current thread becomes
* disabled for thread scheduling purposes and lies dormant until the
* lock has been acquired.
*/
public void lock(T resource) {
activeLocks.compute(resource, (k, v) -> {
ActiveLock lock;
try {
if (v == null) {
// 锁为空，则在锁对象池中创建并借出
lock = lockPool.borrowObject();
} else {
lock = v;
}
// 增加锁引用计数
lock.incrementActiveCount();
} catch (Exception ex) {
LOG.error("Unable to obtain lock.", ex);
throw new RuntimeException(ex);
}
return lock;
//得到锁后进行锁的lock操作
}).lock();
}
/**
* Releases the lock on given resource.
*/
public void unlock(T resource) {
ActiveLock lock = activeLocks.get(resource);
if (lock == null) {
// Someone is releasing a lock which was never acquired. Log and return.
LOG.warn("Trying to release the lock on {}, which was never acquired.",
resource);
return;
}
lock.unlock();
activeLocks.computeIfPresent(resource, (k, v) -> {
v.decrementActiveCount();
if (v.getActiveLockCount() != 0) {
return v;
}
// 如果锁没有被引用了，则在锁对象池中移出此锁
lockPool.returnObject(v);
return null;
});
}
}

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/**
* 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 with the License.
* You may obtain a copy of the License at
* <p>
* http://www.apache.org/licenses/LICENSE-2.0
* <p>
* 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 org.apache.hadoop.ozone.lock;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* Lock implementation which also maintains counter.
*/
public final class ActiveLock {
private Lock lock;
private AtomicInteger count;
/**
* Use ActiveLock#newInstance to create instance.
*/
private ActiveLock() {
this.lock = new ReentrantLock();
this.count = new AtomicInteger(0);
}
/**
* Creates a new instance of ActiveLock.
*
* @return new ActiveLock
*/
public static ActiveLock newInstance() {
return new ActiveLock();
}
/**
* Acquires the lock.
*
* <p>If the lock is not available then the current thread becomes
* disabled for thread scheduling purposes and lies dormant until the
* lock has been acquired.
*/
public void lock() {
lock.lock();
}
/**
* Releases the lock.
*/
public void unlock() {
lock.unlock();
}
/**
* Increment the active count of the lock.
*/
void incrementActiveCount() {
count.incrementAndGet();
}
/**
* Decrement the active count of the lock.
*/
void decrementActiveCount() {
count.decrementAndGet();
}
/**
* Returns the active count on the lock.
*
* @return Number of active leases on the lock.
*/
int getActiveLockCount() {
return count.get();
}
/**
* Resets the active count on the lock.
*/
void resetCounter() {
count.set(0);
}
@Override
public String toString() {
return lock.toString();
}
}