org.apache.hadoop.util.CloseableReferenceCount Maven / Gradle / Ivy
/**
* 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.util;
import java.nio.channels.AsynchronousCloseException;
import java.nio.channels.ClosedChannelException;
import java.util.concurrent.atomic.AtomicInteger;
import org.apache.hadoop.thirdparty.com.google.common.base.Preconditions;
/**
* A closeable object that maintains a reference count.
*
* Once the object is closed, attempting to take a new reference will throw
* ClosedChannelException.
*/
public class CloseableReferenceCount {
/**
* Bit mask representing a closed domain socket.
*/
private static final int STATUS_CLOSED_MASK = 1 << 30;
/**
* The status bits.
*
* Bit 30: 0 = open, 1 = closed.
* Bits 29 to 0: the reference count.
*/
private final AtomicInteger status = new AtomicInteger(0);
public CloseableReferenceCount() { }
/**
* Increment the reference count.
*
* @throws ClosedChannelException If the status is closed.
*/
public void reference() throws ClosedChannelException {
int curBits = status.incrementAndGet();
if ((curBits & STATUS_CLOSED_MASK) != 0) {
status.decrementAndGet();
throw new ClosedChannelException();
}
}
/**
* Decrement the reference count.
*
* @return True if the object is closed and has no outstanding
* references.
*/
public boolean unreference() {
int newVal = status.decrementAndGet();
Preconditions.checkState(newVal != 0xffffffff,
"called unreference when the reference count was already at 0.");
return newVal == STATUS_CLOSED_MASK;
}
/**
* Decrement the reference count, checking to make sure that the
* CloseableReferenceCount is not closed.
*
* @throws AsynchronousCloseException If the status is closed.
*/
public void unreferenceCheckClosed() throws ClosedChannelException {
int newVal = status.decrementAndGet();
if ((newVal & STATUS_CLOSED_MASK) != 0) {
throw new AsynchronousCloseException();
}
}
/**
* Return true if the status is currently open.
*
* @return True if the status is currently open.
*/
public boolean isOpen() {
return ((status.get() & STATUS_CLOSED_MASK) == 0);
}
/**
* Mark the status as closed.
*
* Once the status is closed, it cannot be reopened.
*
* @return The current reference count.
* @throws ClosedChannelException If someone else closes the object
* before we do.
*/
public int setClosed() throws ClosedChannelException {
while (true) {
int curBits = status.get();
if ((curBits & STATUS_CLOSED_MASK) != 0) {
throw new ClosedChannelException();
}
if (status.compareAndSet(curBits, curBits | STATUS_CLOSED_MASK)) {
return curBits & (~STATUS_CLOSED_MASK);
}
}
}
/**
* Get the current reference count.
*
* @return The current reference count.
*/
public int getReferenceCount() {
return status.get() & (~STATUS_CLOSED_MASK);
}
}