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From "John Doe (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-15429) unsynchronized index causes DataInputByteBuffer$Buffer.read hangs
Date Mon, 30 Apr 2018 17:35:00 GMT
John Doe created HADOOP-15429:
---------------------------------

             Summary: unsynchronized index causes DataInputByteBuffer$Buffer.read hangs
                 Key: HADOOP-15429
                 URL: https://issues.apache.org/jira/browse/HADOOP-15429
             Project: Hadoop Common
          Issue Type: Bug
          Components: io
    Affects Versions: 0.23.0
            Reporter: John Doe


In DataInputByteBuffer$Buffer class, the fields bidx and buffers, etc are unsynchronized when
used in read() and reset() function. In certain circumstances, e.g., the reset() is invoked
in a loop, the unsynchronized bidx and buffers triggers a concurrency bug.
Here is the code snippet.

{code:java}
    ByteBuffer[] buffers = new ByteBuffer[0];
    int bidx, pos, length;

    @Override
    public int read(byte[] b, int off, int len) {
      if (bidx >= buffers.length) {
        return -1;
      }
      int cur = 0;
      do {
        int rem = Math.min(len, buffers[bidx].remaining());
        buffers[bidx].get(b, off, rem);
        cur += rem;
        off += rem;
        len -= rem;
      } while (len > 0 && ++bidx < buffers.length); //bidx is unsynchronized
      pos += cur;
      return cur;
    }

    public void reset(ByteBuffer[] buffers) {//if one thread keeps calling reset() in a loop
      bidx = pos = length = 0;
      this.buffers = buffers;
      for (ByteBuffer b : buffers) {
        length += b.remaining();
      }
    }
{code}




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