Examples of com.linkedin.databus.core.util.BufferPosition

com.linkedin.databus.core.util.BufferPosition

"Addresses" used in EventBuffer are encoded with 3 elements:

 1. GenId : The rotation level on which this address is relevant 2. Index : The buffer in the List of ByteBuffers where the address is present 3. Offset : Offset into the buffer. 63                      n                          m                        0 ----------------------------------------------------------------------------- |                       |                          |                        | |    GenId              |       Index              |  Offset                | |                       |                          |                        | -----------------------------------------------------------------------------

In the above diagram, m bits are assigned to Offset, which implies the size of individual buffer <= 2^m; n-m bits are assigned to Index, implying the number of buffers <= 2 ^(n-m); and the rest of the bits (except the sign bit) are for GenId. More info on GenId: Each time the event buffer wraps around, we increment the global genId. So, by keeping the genId encoded in the most significant bit positions, we can get the natural temporal ordering of events in the address-space.

 ================ Important NOTE  ======================= BufferPosition values are not resilient to event buffer restarts.  So DO NOT use the raw values directly in checkpointing and other places that are expected to have a longer lifetime than one run of the relay or client containing the event buffer. =========================================================


    _scnIndex = new ScnIndex(maxIndexSize, maxEventBufferSize, _maxBufferSize, _bufferPositionParser,
                             allocationPolicy, restoreBuffers, _mmapSessionDirectory, _assertLevel,
                             enableScnIndex, _eventFactory.getByteOrder());


    _head = new BufferPosition(_bufferPositionParser, _buffers);
    _tail = new BufferPosition(_bufferPositionParser, _buffers);
    _currentWritePosition = new BufferPosition(_bufferPositionParser, _buffers);
    _eventStartIndex = new BufferPosition(_bufferPositionParser, _buffers);


    _rwLockProvider = new RangeBasedReaderWriterLock();


    LOG.info ( "Trace Relay Option : " + traceOption.getOption() + " physicalPartition:" + _physicalPartition.getName() + " pSourceName:" + _physicalPartition );
    if (RelayEventTraceOption.Option.file == traceOption.getOption())

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    // subsequent call to setNextFreePos(), which calls moveCurrentWritePosition(),
    // blows up.  By normalizing the end position, we effectively block until the
    // head can advance to the same position (or beyond), i.e., until all iterators
    // have caught up, which allows setNextFreePos()/moveCurrentWritePosition() to
    // succeed.  See DDSDBUS-1816 for even more details.
    final BufferPosition normalizedWriteEndPos = new BufferPosition(writeEndPos,
                                                                    _bufferPositionParser,
                                                                    _buffers);
    normalizedWriteEndPos.skipOverFreeSpace();


    boolean interrupted = false;


    if (!empty())
    {
      if (QueuePolicy.BLOCK_ON_WRITE == _queueingPolicy)
      {
        interrupted = waitForReadEventsFreeSpace(logDebugEnabled, writeStartPos,
                                                 normalizedWriteEndPos.getPosition());
      }
      else
      {
        freeUpSpaceForReadEvents(logDebugEnabled, writeStartPos,
                                 normalizedWriteEndPos.getPosition());
      }
    }
    if (logDebugEnabled)
    {
      _log.debug("ensureFreeSpace: writeStart:" + _bufferPositionParser.toString(writeStartPos, _buffers) +
                 "; writeEnd:" + _bufferPositionParser.toString(writeEndPos, _buffers) +
                 "; normalizedWriteEnd:" + normalizedWriteEndPos +
                 "; head:" + _head + "; tail:" + _tail +
                 "; interrupted:" + interrupted);
    }
    assert interrupted || !overwritesHead(writeStartPos, normalizedWriteEndPos.getPosition());


    return interrupted;
  }

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    protected DbusEventInternalWritable _iteratingEvent;  // TODO Make this readable
    protected String _identifier;


    public BaseEventIterator(long head, long tail, String iteratorName)
    {
      _currentPosition = new BufferPosition(_bufferPositionParser,_buffers);
      _currentPosition.setPosition(head);


      _iteratorTail = new BufferPosition(_bufferPositionParser,_buffers);
      _iteratorTail.setPosition(tail);
      _iteratingEvent = _eventFactory.createWritableDbusEvent();
      reset(head, tail, iteratorName);
      trackIterator(this);
    }

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    appender.run();


    log.info("Dbus Event Buffer is :" + dbusBuf);
    log.info("SCNIndex is :" + dbusBuf.getScnIndex());


    final BufferPosition headPos = new BufferPosition(dbusBuf.getHead(),
                                                      dbusBuf.getBufferPositionParser(),
                                                      dbusBuf.getBuffer());
    final BufferPosition tailPos = new BufferPosition(dbusBuf.getTail(),
                                                      dbusBuf.getBufferPositionParser(),
                                                      dbusBuf.getBuffer());
    Assert.assertEquals(0, headPos.bufferGenId());
    Assert.assertEquals(0, headPos.bufferIndex());
    Assert.assertEquals(9629, headPos.bufferOffset());
    Assert.assertEquals(1, tailPos.bufferGenId());
    Assert.assertEquals(0, tailPos.bufferIndex());
    Assert.assertEquals(9416, tailPos.bufferOffset());
    Assert.assertEquals(9984, dbusBuf.getBuffer()[0].limit());
    dbusBuf.getScnIndex().assertHeadPosition(dbusBuf.getHead());


    final BufferPosition lastWinStart = new BufferPosition(61 + 22 * 416,
                                                           dbusBuf.getBufferPositionParser(),
                                                           dbusBuf.getBuffer());
    dbusBuf.getScnIndex().assertLastWrittenPos(lastWinStart);


    long lastScn = events.get(events.size() - 1).sequence();

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Related Classes of com.linkedin.databus.core.util.BufferPosition

com.linkedin.databus.core.DbusEventBuffer

com.linkedin.databus.core.DbusEventBuffer$BaseEventIterator

com.linkedin.databus.core.TestDbusEventBuffer

java.nio.ByteBuffer

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