io.undertow.util.ReferenceCountedPooled Maven / Gradle / Ivy
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* Copyright 2014 Red Hat, Inc., and individual contributors
* as indicated by the @author tags.
*
* Licensed 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 io.undertow.util;
import io.undertow.UndertowMessages;
import io.undertow.connector.PooledByteBuffer;
import java.nio.ByteBuffer;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
/**
* A reference counted pooled implementation, that basically consists of a main buffer, that can be sliced off into smaller buffers,
* and the underlying buffer will not be freed until all the slices and the main buffer itself have also been freed.
*
* This also supports the notion of un-freeing the main buffer. Basically this allows the buffer be re-used, so if only a small slice of the
* buffer was used for read operations the main buffer can potentially be re-used. This prevents buffer exhaustion attacks where content
* is sent in many small packets, and you end up allocating a large number of buffers to hold a small amount of data.
*
* @author Stuart Douglas
*/
public class ReferenceCountedPooled implements PooledByteBuffer {
private final PooledByteBuffer underlying;
@SuppressWarnings("unused")
private volatile int referenceCount;
boolean mainFreed = false;
private ByteBuffer slice = null;
private final FreeNotifier freeNotifier;
private static final AtomicIntegerFieldUpdater referenceCountUpdater = AtomicIntegerFieldUpdater.newUpdater(ReferenceCountedPooled.class, "referenceCount");
public ReferenceCountedPooled(PooledByteBuffer underlying, int referenceCount) {
this(underlying, referenceCount, null);
}
public ReferenceCountedPooled(PooledByteBuffer underlying, int referenceCount, FreeNotifier freeNotifier) {
this.underlying = underlying;
this.referenceCount = referenceCount;
this.freeNotifier = freeNotifier;
}
@Override
public void close() {
if(mainFreed) {
return;
}
mainFreed = true;
freeInternal();
}
@Override
public boolean isOpen() {
return !mainFreed;
}
public boolean isFreed() {
return mainFreed;
}
public boolean tryUnfree() {
int refs;
do {
refs = referenceCountUpdater.get(this);
if(refs <= 0) {
return false;
}
} while (!referenceCountUpdater.compareAndSet(this, refs, refs + 1));
ByteBuffer resource = slice != null ? slice : underlying.getBuffer();
resource.position(resource.limit());
resource.limit(resource.capacity());
slice = resource.slice();
mainFreed = false;
return true;
}
private void freeInternal() {
if(referenceCountUpdater.decrementAndGet(this) == 0) {
underlying.close();
if(freeNotifier != null) {
freeNotifier.freed();
}
}
}
@Override
public ByteBuffer getBuffer() throws IllegalStateException {
if(mainFreed) {
throw UndertowMessages.MESSAGES.bufferAlreadyFreed();
}
if(slice != null) {
return slice;
}
return underlying.getBuffer();
}
public PooledByteBuffer createView(int viewSize) {
ByteBuffer newView = getBuffer().duplicate();
newView.limit(newView.position() + viewSize);
final ByteBuffer newValue = newView.slice();
ByteBuffer newUnderlying = getBuffer().duplicate();
newUnderlying.position(newUnderlying.position() + viewSize);
int oldRemaining = newUnderlying.remaining();
newUnderlying.limit(newUnderlying.capacity());
newUnderlying = newUnderlying.slice();
newUnderlying.limit(newUnderlying.position() + oldRemaining);
slice = newUnderlying;
increaseReferenceCount();
return new PooledByteBuffer() {
boolean free = false;
@Override
public void close() {
//make sure that a given view can only be freed once
if(!free) {
free = true;
ReferenceCountedPooled.this.freeInternal();
}
}
@Override
public boolean isOpen() {
return !free;
}
@Override
public ByteBuffer getBuffer() throws IllegalStateException {
if(free) {
throw UndertowMessages.MESSAGES.bufferAlreadyFreed();
}
return newValue;
}
@Override
public String toString() {
return "ReferenceCountedPooled$view{" +
"buffer=" + newValue +
"free=" + free +
"underlying=" + underlying +
", referenceCount=" + referenceCount +
", mainFreed=" + mainFreed +
", slice=" + slice +
'}';
}
};
}
public PooledByteBuffer createView() {
return createView(getBuffer().remaining());
}
public void increaseReferenceCount() {
int val;
do {
val = referenceCountUpdater.get(this);
if(val == 0) {
//should never happen, as this should only be called from
//code that already has a reference
throw UndertowMessages.MESSAGES.objectWasFreed();
}
} while (!referenceCountUpdater.compareAndSet(this, val, val + 1));
}
public interface FreeNotifier {
void freed();
}
@Override
public String toString() {
return "ReferenceCountedPooled{" +
"underlying=" + underlying +
", referenceCount=" + referenceCount +
", mainFreed=" + mainFreed +
", slice=" + slice +
'}';
}
}