/*
* Copyright © 2014 Cask Data, Inc.
*
* 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 co.cask.cdap.internal.pipeline;
import co.cask.cdap.pipeline.Context;
import co.cask.cdap.pipeline.Stage;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import org.apache.twill.common.Threads;
import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
/**
* Concrete implementation of asynchronous {@link co.cask.cdap.pipeline.Pipeline}.
* <p>
* Input from each {@link co.cask.cdap.pipeline.Stage} is passed to next {@link co.cask.cdap.pipeline.Stage}.
* Before processing to next {@link co.cask.cdap.pipeline.Stage}, we wait for results
* to be available.
* </p>
*
* @param <T> Type of object produced by this pipeline.
*/
public final class AsynchronousPipeline<T> extends AbstractPipeline<T> {
private ListeningExecutorService service;
public AsynchronousPipeline() {
this.service =
MoreExecutors.listeningDecorator(
Executors.newSingleThreadExecutor(Threads.createDaemonThreadFactory("pipeline-executor")));
}
/**
* Executes a pipeline in asynchronous mode.
* <p>
* Waits for the results of previous to be available to move to next
* stage of processing.
* </p>
*
* @param o argument to run the pipeline.
*/
@SuppressWarnings("unchecked")
@Override
public ListenableFuture<T> execute(final Object o) {
return service.submit(new Callable<T>() {
@Override
public T call() throws Exception {
Object input = o;
Object output = null;
for (Stage stage : getStages()) {
Context ctx = new StageContext(input);
stage.process(ctx);
output = ctx.getDownStream();
input = output; // Output of previous stage is input to next stage.
}
return (T) output;
}
});
}
}