| /* |
| * 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.cassandra.cache; |
| |
| import java.util.concurrent.atomic.AtomicIntegerFieldUpdater; |
| |
| import org.apache.cassandra.io.util.Memory; |
| |
| public class RefCountedMemory extends Memory implements AutoCloseable |
| { |
| private volatile int references = 1; |
| private static final AtomicIntegerFieldUpdater<RefCountedMemory> UPDATER = AtomicIntegerFieldUpdater.newUpdater(RefCountedMemory.class, "references"); |
| |
| public RefCountedMemory(long size) |
| { |
| super(size); |
| } |
| |
| /** |
| * @return true if we succeed in referencing before the reference count reaches zero. |
| * (A FreeableMemory object is created with a reference count of one.) |
| */ |
| public boolean reference() |
| { |
| while (true) |
| { |
| int n = UPDATER.get(this); |
| if (n <= 0) |
| return false; |
| if (UPDATER.compareAndSet(this, n, n + 1)) |
| return true; |
| } |
| } |
| |
| /** decrement reference count. if count reaches zero, the object is freed. */ |
| public void unreference() |
| { |
| if (UPDATER.decrementAndGet(this) == 0) |
| super.free(); |
| } |
| |
| public RefCountedMemory copy(long newSize) |
| { |
| RefCountedMemory copy = new RefCountedMemory(newSize); |
| copy.put(0, this, 0, Math.min(size(), newSize)); |
| return copy; |
| } |
| |
| public void free() |
| { |
| throw new AssertionError(); |
| } |
| |
| public void close() |
| { |
| unreference(); |
| } |
| } |