/**
* 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.waveprotocol.wave.client.concurrencycontrol;
import com.google.common.base.Preconditions;
import org.waveprotocol.wave.model.operation.Operation;
import org.waveprotocol.wave.model.operation.SilentOperationSink;
import org.waveprotocol.wave.model.util.CollectionUtils;
import java.util.Queue;
/**
* A sink that proxies for another sink. This sink is usable immediately after
* construction. Operations that are consumed before the target sink is set are
* simply queued. Setting the target sink flushes any operations that have been
* queued. The target can be set only once, and after it is set, this sink
* routes all operations to it.
*
*/
public final class ProxyOperationSink<O extends Operation<?>> implements SilentOperationSink<O> {
private Queue<O> queue;
private SilentOperationSink<O> target;
private ProxyOperationSink() {
}
/**
* Creates a proxy sink.
*/
public static <O extends Operation<?>> ProxyOperationSink<O> create() {
return new ProxyOperationSink<O>();
}
/**
* Sets this proxy's target. Any operations previously consumed by this proxy
* will be forwarded to the target synchronously within this method. Future
* operations consumed by this proxy will be sent directly to the target. This
* target can be set at most once.
*
* @param target target to consume future operations
*/
public void setTarget(SilentOperationSink<O> target) {
Preconditions.checkState(this.target == null);
this.target = target;
if (queue != null) {
while (!queue.isEmpty()) {
target.consume(queue.poll());
}
queue = null;
}
}
@Override
public void consume(O op) {
if (target != null) {
target.consume(op);
} else {
if (queue == null) {
queue = CollectionUtils.createQueue();
}
queue.add(op);
}
}
}