Class MultiProducerSequencer

java.lang.Object
com.lmax.disruptor.AbstractSequencer
com.lmax.disruptor.MultiProducerSequencer
All Implemented Interfaces:
Cursored, Sequenced, Sequencer

public final class MultiProducerSequencer extends AbstractSequencer

Coordinator for claiming sequences for access to a data structure while tracking dependent Sequences. Suitable for use for sequencing across multiple publisher threads.

* Note on Cursored.getCursor(): With this sequencer the cursor value is updated after the call to Sequenced.next(), to determine the highest available sequence that can be read, then Sequencer.getHighestPublishedSequence(long, long) should be used.

  • Field Details

    • UNSAFE

      private static final sun.misc.Unsafe UNSAFE
    • BASE

      private static final long BASE
    • SCALE

      private static final long SCALE
    • gatingSequenceCache

      private final Sequence gatingSequenceCache
    • availableBuffer

      private final int[] availableBuffer
    • indexMask

      private final int indexMask
    • indexShift

      private final int indexShift
  • Constructor Details

    • MultiProducerSequencer

      public MultiProducerSequencer(int bufferSize, WaitStrategy waitStrategy)
      Construct a Sequencer with the selected wait strategy and buffer size.
      Parameters:
      bufferSize - the size of the buffer that this will sequence over.
      waitStrategy - for those waiting on sequences.
  • Method Details

    • hasAvailableCapacity

      public boolean hasAvailableCapacity(int requiredCapacity)
      Description copied from interface: Sequenced
      Has the buffer got capacity to allocate another sequence. This is a concurrent method so the response should only be taken as an indication of available capacity.
      Parameters:
      requiredCapacity - in the buffer
      Returns:
      true if the buffer has the capacity to allocate the next sequence otherwise false.
      See Also:
    • hasAvailableCapacity

      private boolean hasAvailableCapacity(Sequence[] gatingSequences, int requiredCapacity, long cursorValue)
    • claim

      public void claim(long sequence)
      Description copied from interface: Sequencer
      Claim a specific sequence. Only used if initialising the ring buffer to a specific value.
      Parameters:
      sequence - The sequence to initialise too.
      See Also:
    • next

      public long next()
      Description copied from interface: Sequenced
      Claim the next event in sequence for publishing.
      Returns:
      the claimed sequence value
      See Also:
    • next

      public long next(int n)
      Description copied from interface: Sequenced
      Claim the next n events in sequence for publishing. This is for batch event producing. Using batch producing requires a little care and some math.
       int n = 10;
       long hi = sequencer.next(n);
       long lo = hi - (n - 1);
       for (long sequence = lo; sequence <= hi; sequence++) {
           // Do work.
       }
       sequencer.publish(lo, hi);
       
      Parameters:
      n - the number of sequences to claim
      Returns:
      the highest claimed sequence value
      See Also:
    • tryNext

      public long tryNext() throws InsufficientCapacityException
      Description copied from interface: Sequenced
      Attempt to claim the next event in sequence for publishing. Will return the number of the slot if there is at least requiredCapacity slots available.
      Returns:
      the claimed sequence value
      Throws:
      InsufficientCapacityException - thrown if there is no space available in the ring buffer.
      See Also:
    • tryNext

      public long tryNext(int n) throws InsufficientCapacityException
      Description copied from interface: Sequenced
      Attempt to claim the next n events in sequence for publishing. Will return the highest numbered slot if there is at least requiredCapacity slots available. Have a look at Sequenced.next() for a description on how to use this method.
      Parameters:
      n - the number of sequences to claim
      Returns:
      the claimed sequence value
      Throws:
      InsufficientCapacityException - thrown if there is no space available in the ring buffer.
      See Also:
    • remainingCapacity

      public long remainingCapacity()
      Description copied from interface: Sequenced
      Get the remaining capacity for this sequencer.
      Returns:
      The number of slots remaining.
      See Also:
    • initialiseAvailableBuffer

      private void initialiseAvailableBuffer()
    • publish

      public void publish(long sequence)
      Description copied from interface: Sequenced
      Publishes a sequence. Call when the event has been filled.
      Parameters:
      sequence - the sequence to be published.
      See Also:
    • publish

      public void publish(long lo, long hi)
      Description copied from interface: Sequenced
      Batch publish sequences. Called when all of the events have been filled.
      Parameters:
      lo - first sequence number to publish
      hi - last sequence number to publish
      See Also:
    • setAvailable

      private void setAvailable(long sequence)
      The below methods work on the availableBuffer flag.

      The prime reason is to avoid a shared sequence object between publisher threads. (Keeping single pointers tracking start and end would require coordination between the threads).

      -- Firstly we have the constraint that the delta between the cursor and minimum gating sequence will never be larger than the buffer size (the code in next/tryNext in the Sequence takes care of that). -- Given that; take the sequence value and mask off the lower portion of the sequence as the index into the buffer (indexMask). (aka modulo operator) -- The upper portion of the sequence becomes the value to check for availability. ie: it tells us how many times around the ring buffer we've been (aka division) -- Because we can't wrap without the gating sequences moving forward (i.e. the minimum gating sequence is effectively our last available position in the buffer), when we have new data and successfully claimed a slot we can simply write over the top.

    • setAvailableBufferValue

      private void setAvailableBufferValue(int index, int flag)
    • isAvailable

      public boolean isAvailable(long sequence)
      Description copied from interface: Sequencer
      Confirms if a sequence is published and the event is available for use; non-blocking.
      Parameters:
      sequence - of the buffer to check
      Returns:
      true if the sequence is available for use, false if not
      See Also:
    • getHighestPublishedSequence

      public long getHighestPublishedSequence(long lowerBound, long availableSequence)
      Description copied from interface: Sequencer
      Get the highest sequence number that can be safely read from the ring buffer. Depending on the implementation of the Sequencer this call may need to scan a number of values in the Sequencer. The scan will range from nextSequence to availableSequence. If there are no available values >= nextSequence the return value will be nextSequence - 1. To work correctly a consumer should pass a value that is 1 higher than the last sequence that was successfully processed.
      Parameters:
      lowerBound - The sequence to start scanning from.
      availableSequence - The sequence to scan to.
      Returns:
      The highest value that can be safely read, will be at least nextSequence - 1.
    • calculateAvailabilityFlag

      private int calculateAvailabilityFlag(long sequence)
    • calculateIndex

      private int calculateIndex(long sequence)