svn commit: r1519841 - /hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java

[cm...@apache.org]

Author: cmccabe
Date: Tue Sep  3 20:38:45 2013
New Revision: 1519841

URL: http://svn.apache.org/r1519841
Log:
HDFS-5121.  Add RPCs for creating and manipulating cache pools.  (Contributed by Colin Patrick McCabe)

Added:
    hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java

Added: hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java
URL: http://svn.apache.org/viewvc/hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java?rev=1519841&view=auto
==============================================================================
--- hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java (added)
+++ hadoop/common/branches/HDFS-4949/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/BatchedRemoteIterator.java Tue Sep  3 20:38:45 2013
@@ -0,0 +1,121 @@
+/**
+ * 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.fs;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+/**
+ * A RemoteIterator that fetches elements in batches.
+ */
+public abstract class BatchedRemoteIterator<K, E> implements RemoteIterator<E> {
+  public interface BatchedEntries<E> {
+    public E get(int i);
+    public int size();
+  }
+  
+  public static class BatchedListEntries<E> implements BatchedEntries<E> {
+    private final List<E> entries;
+
+    public BatchedListEntries(List<E> entries) {
+      this.entries = entries;
+    }
+
+    public E get(int i) {
+      return entries.get(i);
+      
+    }
+
+    public int size() {
+      return entries.size();
+    }
+  }
+
+  private K nextKey;
+  private final int maxRepliesPerRequest;
+  private BatchedEntries<E> entries;
+  private int idx;
+
+  public BatchedRemoteIterator(K nextKey, int maxRepliesPerRequest) {
+    this.nextKey = nextKey;
+    this.maxRepliesPerRequest = maxRepliesPerRequest;
+    this.entries = null;
+    this.idx = -1;
+  }
+
+  /**
+   * Perform the actual remote request.
+   *
+   * @param key                    The key to send.
+   * @param maxRepliesPerRequest   The maximum number of replies to allow.
+   * @return                       A list of replies.
+   */
+  public abstract BatchedEntries<E> makeRequest(K nextKey, int maxRepliesPerRequest)
+      throws IOException;
+
+  private void makeRequest() throws IOException {
+    idx = 0;
+    entries = null;
+    entries = makeRequest(nextKey, maxRepliesPerRequest);
+    if (entries.size() > maxRepliesPerRequest) {
+      throw new IOException("invalid number of replies returned: got " +
+          entries.size() + ", expected " + maxRepliesPerRequest +
+          " at most.");
+    }
+    if (entries.size() == 0) {
+      entries = null;
+    }
+  }
+
+  private void makeRequestIfNeeded() throws IOException {
+    if (idx == -1) {
+      makeRequest();
+    } else if ((entries != null) && (idx >= entries.size())) {
+      if (entries.size() < maxRepliesPerRequest) {
+        // Last time, we got fewer entries than requested.
+        // So we should be at the end.
+        entries = null;
+      } else {
+        makeRequest();
+      }
+    }
+  }
+
+  @Override
+  public boolean hasNext() throws IOException {
+    makeRequestIfNeeded();
+    return (entries != null);
+  }
+
+  /**
+   * Return the next list key associated with an element.
+   */
+  public abstract K elementToNextKey(E element);
+
+  @Override
+  public E next() throws IOException {
+    makeRequestIfNeeded();
+    if (entries == null) {
+      throw new NoSuchElementException();
+    }
+    E entry = entries.get(idx++);
+    nextKey = elementToNextKey(entry);
+    return entry;
+  }
+}