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Date: Tue, 9 Dec 2014 16:42:12 +0000 (UTC)
From: "ASF GitHub Bot (JIRA)" <jira@apache.org>
To: issues@flink.incubator.apache.org
Message-ID: <JIRA.12723844.1403778059000.110515.1418143332439@Atlassian.JIRA>
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 <JIRA.12723844.1403778059099@arcas>
Subject: [jira] [Commented] (FLINK-986) Add intermediate results to
 distributed runtime
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    [ https://issues.apache.org/jira/browse/FLINK-986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14239631#comment-14239631 ] 

ASF GitHub Bot commented on FLINK-986:
--------------------------------------

Github user StephanEwen commented on a diff in the pull request:

    https://github.com/apache/incubator-flink/pull/254#discussion_r21541216
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/io/network/buffer/Buffer.java ---
    @@ -0,0 +1,124 @@
    +/*
    + * 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.flink.runtime.io.network.buffer;
    +
    +import org.apache.flink.core.memory.MemorySegment;
    +
    +import java.nio.ByteBuffer;
    +import java.util.concurrent.atomic.AtomicInteger;
    +
    +import static com.google.common.base.Preconditions.checkArgument;
    +import static com.google.common.base.Preconditions.checkNotNull;
    +import static com.google.common.base.Preconditions.checkState;
    +
    +/**
    + * Wrapper for pooled {@link MemorySegment} instances.
    + */
    +public class Buffer {
    +
    +	/** Size of the backing {@link MemorySegment} instance */
    +	private final MemorySegment memorySegment;
    +
    +	/** The recycler for the backing {@link MemorySegment} */
    +	private final BufferRecycler recycler;
    +
    +	/** The current number of references to this buffer */
    +	private AtomicInteger referenceCount = new AtomicInteger(1);
    +
    +	/**
    +	 * The current size of the buffer in the range from 0 (inclusive) to the
    +	 * size of the backing {@link MemorySegment} (inclusive).
    +	 */
    +	private AtomicInteger currentSize = new AtomicInteger();
    +
    +	public Buffer(MemorySegment memorySegment, BufferRecycler recycler) {
    +		this.memorySegment = checkNotNull(memorySegment);
    +		this.currentSize.set(memorySegment.size());
    +		this.recycler = checkNotNull(recycler);
    +	}
    +
    +	// TODO Revert serialized encoding of buffer or event type
    +	public boolean isBuffer() {
    +		ensureNotRecycled();
    +
    +		return memorySegment.getBoolean(0);
    +	}
    +
    +	public MemorySegment getMemorySegment() {
    +		ensureNotRecycled();
    +
    +		return memorySegment;
    +	}
    +
    +	public ByteBuffer getNioBuffer() {
    +		ensureNotRecycled();
    +
    +		return memorySegment.wrap(0, currentSize.get()).duplicate();
    +	}
    +
    +	public int getSize() {
    +		ensureNotRecycled();
    +
    +		return currentSize.get();
    +	}
    +
    +	public void setSize(int newSize) {
    +		ensureNotRecycled();
    +
    +		currentSize.set(checkSizeWithinBounds(newSize));
    +	}
    +
    +	public void recycle() {
    +		int current = referenceCount.decrementAndGet();
    --- End diff --
    
    This logic is not safe against concurrent reference increments / decrements. Here is how we can do it:
    
    The constructor should initialize the number of references to 1
    
    ```
    public void retain() {
      while (true) {
        int current = referenceCount.get();
        if (current > 0) {
          if (referenceCount.compareAndSet(current, current + 1)) {
            break;
          } // else fall through the loop
        } else {
          throw new IllegalStateException("released");
        }
      }
    }
    
    public void release() {
      int newCount = referenceCount.decrementAndGet();
      if (newCount ==  0) {
        recycle();
      } else if (newCount < 0) {
        throw new IllegalStateException("Already disposed before");
      }
    }
    ```


> Add intermediate results to distributed runtime
> -----------------------------------------------
>
>                 Key: FLINK-986
>                 URL: https://issues.apache.org/jira/browse/FLINK-986
>             Project: Flink
>          Issue Type: New Feature
>          Components: Distributed Runtime
>            Reporter: Ufuk Celebi
>            Assignee: Ufuk Celebi
>            Priority: Blocker
>
> Support for intermediate results in the runtime is currently blocking different efforts like fault tolerance or result collection at the client.


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