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  1. Hadoop Common
  2. HADOOP-11039

ByteBufferReadable API doc is inconsistent with the implementations.

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Details

    • Bug
    • Status: Closed
    • Minor
    • Resolution: Fixed
    • None
    • 2.7.0
    • documentation
    • None

    Description

      In ByteBufferReadable, API doc of int read(ByteBuffer buf) says:

      After a successful call, buf.position() and buf.limit() should be unchanged, and therefore any data can be immediately read from buf. buf.mark() may be cleared or updated.

      @param buf
      the ByteBuffer to receive the results of the read operation. Up to
      buf.limit() - buf.position() bytes may be read.

      But actually the implementations (e.g. DFSInputStream, RemoteBlockReader2) would be:
      Upon return, buf.position() will be advanced by the number of bytes read.
      code implementation of RemoteBlockReader2 is as following:

      @Override
        public int read(ByteBuffer buf) throws IOException {
          if (curDataSlice == null || curDataSlice.remaining() == 0 && bytesNeededToFinish > 0) {
            readNextPacket();
          }
          if (curDataSlice.remaining() == 0) {
            // we're at EOF now
            return -1;
          }
      
          int nRead = Math.min(curDataSlice.remaining(), buf.remaining());
          ByteBuffer writeSlice = curDataSlice.duplicate();
          writeSlice.limit(writeSlice.position() + nRead);
          buf.put(writeSlice);
          curDataSlice.position(writeSlice.position());
      
          return nRead;
        }
      

      This description is very important and will guide user how to use this API, and all the implementations should keep the same behavior. We should fix the javadoc.

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            hitliuyi Yi Liu Assign to me
            hitliuyi Yi Liu
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