[GitHub] taegeonum commented on a change in pull request #125: [NEMO-128] Support Beam UnboundedSource

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taegeonum commented on a change in pull request #125: [NEMO-128] Support Beam UnboundedSource
URL: https://github.com/apache/incubator-nemo/pull/125#discussion_r226522564
 
 

 ##########
 File path: compiler/frontend/beam/src/main/java/org/apache/nemo/compiler/frontend/beam/source/BeamUnboundedSourceVertex.java
 ##########
 @@ -0,0 +1,176 @@
+/*
+ * Copyright (C) 2018 Seoul National University
+ *
+ * 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 org.apache.nemo.compiler.frontend.beam.source;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import org.apache.beam.sdk.io.UnboundedSource;
+import org.apache.beam.sdk.util.WindowedValue;
+import org.apache.nemo.common.ir.Readable;
+import org.apache.nemo.common.ir.vertex.IRVertex;
+import org.apache.nemo.common.ir.vertex.SourceVertex;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * SourceVertex implementation for UnboundedSource.
+ * @param <O> output type.
+ * @param <M> checkpoint mark type.
+ */
+public final class BeamUnboundedSourceVertex<O, M extends UnboundedSource.CheckpointMark> extends
+  SourceVertex<WindowedValue<O>> {
+
+  private static final Logger LOG = LoggerFactory.getLogger(BeamUnboundedSourceVertex.class.getName());
+  private UnboundedSource<O, M> source;
+  private final String sourceDescription;
+
+  /**
+   * The default constructor for beam unbounded source.
+   * @param source unbounded source.
+   */
+  public BeamUnboundedSourceVertex(final UnboundedSource<O, M> source) {
+    super();
+    this.source = source;
+    this.sourceDescription = source.toString();
+  }
+
+  private BeamUnboundedSourceVertex(final BeamUnboundedSourceVertex<O, M> that) {
+    super(that);
+    this.source = that.source;
+    this.sourceDescription = that.source.toString();
+  }
+
+  @Override
+  public IRVertex getClone() {
+    return new BeamUnboundedSourceVertex<>(this);
+  }
+
+  @Override
+  public List<Readable<WindowedValue<O>>> getReadables(final int desiredNumOfSplits) throws Exception {
+    final List<Readable<WindowedValue<O>>> readables = new ArrayList<>();
+    source.split(desiredNumOfSplits, null)
+      .forEach(unboundedSource -> readables.add(new UnboundedSourceReadable<>(unboundedSource)));
+    return readables;
+  }
+
+  @Override
+  public void clearInternalStates() {
+    source = null;
+  }
+
+  @Override
+  public ObjectNode getPropertiesAsJsonNode() {
+    final ObjectNode node = getIRVertexPropertiesAsJsonNode();
+    node.put("source", sourceDescription);
+    return node;
+  }
+
+  /**
+   * UnboundedSourceReadable class.
+   * @param <O> output type.
+   * @param <M> checkpoint mark type.
+   */
+  private static final class UnboundedSourceReadable<O, M extends UnboundedSource.CheckpointMark>
+      implements Readable<WindowedValue<O>> {
+    private final UnboundedSource<O, M> unboundedSource;
+
+    UnboundedSourceReadable(final UnboundedSource<O, M> unboundedSource) {
+      this.unboundedSource = unboundedSource;
+    }
+
+    @Override
+    public Iterable<WindowedValue<O>> read() throws IOException {
+      return new UnboundedSourceIterable<>(unboundedSource);
+    }
+
+    @Override
+    public List<String> getLocations() throws Exception {
+      return null;
+    }
+  }
+
+  /**
+   * The iterable class for unbounded sources.
+   * @param <O> output type.
+   * @param <M> checkpoint mark type.
+   */
+  private static final class UnboundedSourceIterable<O, M extends UnboundedSource.CheckpointMark>
+      implements Iterable<WindowedValue<O>> {
+
+    private UnboundedSourceIterator<O, M> iterator;
+
+    UnboundedSourceIterable(final UnboundedSource<O, M> unboundedSource) throws IOException {
+      this.iterator = new UnboundedSourceIterator<>(unboundedSource);
+    }
+
+    @Override
+    public Iterator<WindowedValue<O>> iterator() {
+      return iterator;
+    }
+  }
+
+  /**
+   * The iterator for unbounded sources.
+   * @param <O> output type.
+   * @param <M> checkpoint mark type.
+   */
+  private static final class UnboundedSourceIterator<O, M extends UnboundedSource.CheckpointMark>
+      implements Iterator<WindowedValue<O>> {
+
+    private final UnboundedSource.UnboundedReader<O> unboundedReader;
+    private boolean available;
+
+    UnboundedSourceIterator(final UnboundedSource<O, M> unboundedSource) throws IOException {
+      this.unboundedReader = unboundedSource.createReader(null, null);
+      available = unboundedReader.start();
+    }
+
+    @Override
+    public boolean hasNext() {
+      // Unbounded source always has next element until it finishes.
+      return true;
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public WindowedValue<O> next() {
+      try {
+        while (true) {
+          if (!available) {
 
 Review comment:
   Where does this variable become true? If it is false, it loops infinitely. 

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