diff --git a/hbase-common/src/main/java/org/apache/hadoop/hbase/util/KeyLocker.java b/hbase-common/src/main/java/org/apache/hadoop/hbase/util/KeyLocker.java
index 5398582..dec91aa 100644
--- a/hbase-common/src/main/java/org/apache/hadoop/hbase/util/KeyLocker.java
+++ b/hbase-common/src/main/java/org/apache/hadoop/hbase/util/KeyLocker.java
@@ -18,49 +18,45 @@
package org.apache.hadoop.hbase.util;
-
-import java.util.HashMap;
+import java.util.Arrays;
+import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
-import java.util.SortedSet;
-import java.util.TreeSet;
-import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
/**
* A utility class to manage a set of locks. Each lock is identified by a String which serves
- * as a key. Typical usage is:
- * class Example{
- * private final static KeyLocker<String> locker = new Locker<String>();
- *
- *
- * public void foo(String s){
- * Lock lock = locker.acquireLock(s);
- * try {
- * // whatever
- * }finally{
- * lock.unlock();
- * }
- * }
+ * as a key. Typical usage is:
*/
@InterfaceAudience.Private
-public class KeyLocker> {
- private static final Log LOG = LogFactory.getLog(KeyLocker.class);
-
+public class KeyLocker {
// The number of lock we want to easily support. It's not a maximum.
private static final int NB_CONCURRENT_LOCKS = 1000;
- // We need an atomic counter to manage the number of users using the lock and free it when
- // it's equal to zero.
- private final Map, AtomicInteger>> locks =
- new HashMap, AtomicInteger>>(NB_CONCURRENT_LOCKS);
+ private final WeakObjectPool lockPool =
+ new WeakObjectPool(
+ new WeakObjectPool.ObjectFactory() {
+ @Override
+ public ReentrantLock createObject(K key) {
+ return new ReentrantLock();
+ }
+ },
+ NB_CONCURRENT_LOCKS);
/**
* Return a lock for the given key. The lock is already locked.
@@ -70,67 +66,36 @@ public class KeyLocker> {
public ReentrantLock acquireLock(K key) {
if (key == null) throw new IllegalArgumentException("key must not be null");
- Pair, AtomicInteger> lock;
- synchronized (this) {
- lock = locks.get(key);
- if (lock == null) {
- lock = new Pair, AtomicInteger>(
- new KeyLock(this, key), new AtomicInteger(1));
- locks.put(key, lock);
- } else {
- lock.getSecond().incrementAndGet();
- }
- }
- lock.getFirst().lock();
- return lock.getFirst();
+ lockPool.purge();
+ ReentrantLock lock = lockPool.get(key);
+
+ lock.lock();
+ return lock;
}
/**
* Acquire locks for a set of keys. The keys will be
* sorted internally to avoid possible deadlock.
+ *
+ * @throw ClassCastException if the given {@code keys}
+ * contains elements that are not mutually comparable
*/
- public Map acquireLocks(final Set keys) {
- Map locks = new HashMap(keys.size());
- SortedSet sortedKeys = new TreeSet(keys);
- for (K key : sortedKeys) {
- locks.put(key, acquireLock(key));
- }
- return locks;
- }
-
- /**
- * Free the lock for the given key.
- */
- private synchronized void releaseLock(K key) {
- Pair, AtomicInteger> lock = locks.get(key);
- if (lock != null) {
- if (lock.getSecond().decrementAndGet() == 0) {
- locks.remove(key);
- }
- } else {
- String message = "Can't release the lock for " + key+", this key is not in the key list." +
- " known keys are: "+ locks.keySet();
- LOG.error(message);
- throw new RuntimeException(message);
- }
- }
-
- static class KeyLock> extends ReentrantLock {
- private static final long serialVersionUID = -12432857283423584L;
+ public Map acquireLocks(Set extends K> keys) {
+ Object[] keyArray = keys.toArray();
+ Arrays.sort(keyArray);
- private final transient KeyLocker locker;
- private final K lockId;
-
- private KeyLock(KeyLocker locker, K lockId) {
- super();
- this.locker = locker;
- this.lockId = lockId;
+ lockPool.purge();
+ Map locks = new LinkedHashMap(keyArray.length);
+ for (Object o : keyArray) {
+ @SuppressWarnings("unchecked")
+ K key = (K)o;
+ ReentrantLock lock = lockPool.get(key);
+ locks.put(key, lock);
}
- @Override
- public void unlock() {
- super.unlock();
- locker.releaseLock(lockId);
+ for (Lock lock : locks.values()) {
+ lock.lock();
}
+ return locks;
}
}
diff --git a/hbase-common/src/main/java/org/apache/hadoop/hbase/util/WeakObjectPool.java b/hbase-common/src/main/java/org/apache/hadoop/hbase/util/WeakObjectPool.java
new file mode 100644
index 0000000..7757c6c
--- /dev/null
+++ b/hbase-common/src/main/java/org/apache/hadoop/hbase/util/WeakObjectPool.java
@@ -0,0 +1,195 @@
+/*
+ * 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
+ *
+ * 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 org.apache.hadoop.hbase.util;
+
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.WeakReference;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import org.apache.hadoop.hbase.classification.InterfaceAudience;
+
+/**
+ * A {@code WeakReference} based shared object pool.
+ * The objects are kept in weak references and
+ * associated with keys which are identified by the {@code equals} method.
+ * The objects are created by {@link ObjectFactory} on demand.
+ * The object creation is expected to be lightweight,
+ * and the objects may be excessively created and discarded.
+ * Thread safe.
+ */
+@InterfaceAudience.Private
+public class WeakObjectPool {
+ /**
+ * An {@code ObjectFactory} object is used to create
+ * new shared objects on demand.
+ */
+ public interface ObjectFactory {
+ /**
+ * Creates a new shared object associated with the given {@code key},
+ * identified by the {@code equals} method.
+ * This method may be simultaneously called by multiple threads
+ * with the same key, and the excessive objects are just discarded.
+ */
+ V createObject(K key);
+ }
+
+ private final ReferenceQueue staleRefQueue = new ReferenceQueue();
+
+ private class ObjectReference extends WeakReference {
+ final K key;
+
+ ObjectReference(K key, V obj) {
+ super(obj, staleRefQueue);
+ this.key = key;
+ }
+ }
+
+ private final ObjectFactory objectFactory;
+
+ /** Does not permit null keys. */
+ private final ConcurrentMap referenceCache;
+
+ /**
+ * The default initial capacity,
+ * used when not otherwise specified in a constructor.
+ */
+ public static final int DEFAULT_INITIAL_CAPACITY = 16;
+
+ /**
+ * The default concurrency level,
+ * used when not otherwise specified in a constructor.
+ */
+ public static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+
+ /**
+ * Creates a new pool with the default initial capacity (16)
+ * and the default concurrency level (16).
+ *
+ * @param objectFactory the factory to supply new objects on demand
+ *
+ * @throws NullPointerException if {@code objectFactory} is null
+ */
+ public WeakObjectPool(ObjectFactory objectFactory) {
+ this(objectFactory, DEFAULT_INITIAL_CAPACITY, DEFAULT_CONCURRENCY_LEVEL);
+ }
+
+ /**
+ * Creates a new pool with the given initial capacity
+ * and the default concurrency level (16).
+ *
+ * @param objectFactory the factory to supply new objects on demand
+ * @param initialCapacity the initial capacity to keep objects in the pool
+ *
+ * @throws NullPointerException if {@code objectFactory} is null
+ * @throws IllegalArgumentException if {@code initialCapacity} is negative
+ */
+ public WeakObjectPool(ObjectFactory objectFactory, int initialCapacity) {
+ this(objectFactory, initialCapacity, DEFAULT_CONCURRENCY_LEVEL);
+ }
+
+ /**
+ * Creates a new pool with the given initial capacity
+ * and the given concurrency level.
+ *
+ * @param objectFactory the factory to supply new objects on demand
+ * @param initialCapacity the initial capacity to keep objects in the pool
+ * @param concurrencyLevel the estimated count of concurrently accessing threads
+ *
+ * @throws NullPointerException if {@code objectFactory} is null
+ * @throws IllegalArgumentException if {@code initialCapacity} is negative or
+ * {@code concurrencyLevel} is non-positive
+ */
+ public WeakObjectPool(
+ ObjectFactory objectFactory,
+ int initialCapacity,
+ int concurrencyLevel) {
+
+ if (objectFactory == null) {
+ throw new NullPointerException();
+ }
+ this.objectFactory = objectFactory;
+
+ this.referenceCache = new ConcurrentHashMap(
+ initialCapacity, 0.75f, concurrencyLevel);
+ // 0.75f is the default load factor threshold of ConcurrentHashMap.
+ }
+
+ /**
+ * Removes stale references of shared objects from the pool.
+ * References newly becoming stale may still remain.
+ * The implementation of this method is expected to be lightweight
+ * when there is no stale reference.
+ */
+ public void purge() {
+ // This method is lightweight while there is no stale reference
+ // with the Oracle (Sun) implementation of {@code ReferenceQueue},
+ // because {@code ReferenceQueue.poll} just checks a volatile instance
+ // variable in {@code ReferenceQueue}.
+
+ while (true) {
+ @SuppressWarnings("unchecked")
+ ObjectReference ref = (ObjectReference)staleRefQueue.poll();
+ if (ref == null) {
+ break;
+ }
+ referenceCache.remove(ref.key, ref);
+ }
+ }
+
+ /**
+ * Returns a shared object associated with the given {@code key},
+ * which is identified by the {@code equals} method.
+ * @throws NullPointerException if {@code key} is null
+ */
+ public V get(K key) {
+ ObjectReference ref = referenceCache.get(key);
+ if (ref != null) {
+ V obj = ref.get();
+ if (obj != null) {
+ return obj;
+ }
+ referenceCache.remove(key, ref);
+ }
+
+ V newObj = objectFactory.createObject(key);
+ ObjectReference newRef = new ObjectReference(key, newObj);
+ while (true) {
+ ObjectReference existingRef = referenceCache.putIfAbsent(key, newRef);
+ if (existingRef == null) {
+ return newObj;
+ }
+
+ V existingObject = existingRef.get();
+ if (existingObject != null) {
+ return existingObject;
+ }
+ referenceCache.remove(key, existingRef);
+ }
+ }
+
+ /**
+ * Returns an estimated count of objects kept in the pool.
+ * This also counts stale references,
+ * and you might want to call {@link #purge()} beforehand.
+ */
+ public int size() {
+ return referenceCache.size();
+ }
+}
diff --git a/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestKeyLocker.java b/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestKeyLocker.java
index 9bb8a04..40b918c 100644
--- a/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestKeyLocker.java
+++ b/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestKeyLocker.java
@@ -30,7 +30,7 @@ import org.junit.experimental.categories.Category;
public class TestKeyLocker {
@Test
public void testLocker(){
- KeyLocker locker = new KeyLocker();
+ KeyLocker locker = new KeyLocker();
ReentrantLock lock1 = locker.acquireLock("l1");
Assert.assertTrue(lock1.isHeldByCurrentThread());
@@ -51,9 +51,19 @@ public class TestKeyLocker {
lock2.unlock();
Assert.assertFalse(lock20.isHeldByCurrentThread());
- // The lock object was freed once useless, so we're recreating a new one
+ // The lock object will be garbage-collected
+ // if you free its reference for a long time,
+ // and you will get a new one at the next time.
+ int lock2Hash = System.identityHashCode(lock2);
+ lock2 = null;
+ lock20 = null;
+
+ System.gc();
+ System.gc();
+ System.gc();
+
ReentrantLock lock200 = locker.acquireLock("l2");
- Assert.assertTrue(lock2 != lock200);
+ Assert.assertNotEquals(lock2Hash, System.identityHashCode(lock200));
lock200.unlock();
Assert.assertFalse(lock200.isHeldByCurrentThread());
diff --git a/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestWeakObjectPool.java b/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestWeakObjectPool.java
new file mode 100644
index 0000000..bf1b4eb
--- /dev/null
+++ b/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestWeakObjectPool.java
@@ -0,0 +1,134 @@
+/*
+ * 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
+ *
+ * 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 org.apache.hadoop.hbase.util;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.apache.hadoop.hbase.testclassification.MiscTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category({MiscTests.class, SmallTests.class})
+public class TestWeakObjectPool {
+ WeakObjectPool pool;
+
+ @Before
+ public void setUp() {
+ pool = new WeakObjectPool(
+ new WeakObjectPool.ObjectFactory() {
+ @Override
+ public Object createObject(String key) {
+ return new Object();
+ }
+ });
+ }
+
+ @Test
+ public void testKeys() {
+ Object obj1 = pool.get("a");
+ Object obj2 = pool.get(new String("a"));
+
+ Assert.assertSame(obj1, obj2);
+
+ Object obj3 = pool.get("b");
+
+ Assert.assertNotSame(obj1, obj3);
+ }
+
+ @Test
+ public void testWeakReference() throws Exception {
+ Object obj1 = pool.get("a");
+ int hash1 = System.identityHashCode(obj1);
+
+ System.gc();
+ System.gc();
+ System.gc();
+
+ Thread.sleep(10);
+ // Sleep a while because references newly becoming stale
+ // may still remain when calling the {@code purge} method.
+ pool.purge();
+ Assert.assertEquals(1, pool.size());
+
+ Object obj2 = pool.get("a");
+ Assert.assertSame(obj1, obj2);
+
+ obj1 = null;
+ obj2 = null;
+
+ System.gc();
+ System.gc();
+ System.gc();
+
+ Thread.sleep(10);
+ pool.purge();
+ Assert.assertEquals(0, pool.size());
+
+ Object obj3 = pool.get("a");
+ Assert.assertNotEquals(hash1, System.identityHashCode(obj3));
+ }
+
+ @Test(timeout=1000)
+ public void testCongestion() throws Exception {
+ final int THREAD_COUNT = 100;
+
+ final AtomicBoolean assertionFailed = new AtomicBoolean();
+ final AtomicReference