Package org.pipecraft.pipes.sync.source

Class QueueReaderPipe<T>

  • Type Parameters:
    T - the queue item data type
    All Implemented Interfaces:
    Closeable, AutoCloseable, BasePipe, Pipe<T>
    public class QueueReaderPipe<T>
extends Object
implements Pipe<T>
    A source pipe reading the contents of a BlockingQueue. Uses special item values as queue end marker indicators. For proper behavior, the same marker references (one for error and one for successful termination) should also be used by the queue producer. This pipe is detached from the producer and has no knowledge on expected item count, therefore progress tracking is not possible and simply jumps from 0.0 to 1.0 once the queue is fully consumed.
    Author:
    Eyal Schneider

    • Constructor Detail

      • QueueReaderPipe

        public QueueReaderPipe​(BlockingQueue<T> queue,
                       T successMarker,
                       T errorMarker)
        Constructor
        Parameters:
        queue - The queue to read from
        successMarker - Used for indicating data completion with success. Should be a unique reference reserved for this purpose.
        errorMarker - Used for indicating an error termination. Should be a unique reference reserved for this purpose. When found, the next() method will throw an exception.

    • Method Detail

      • start

        public void start()
           throws PipeException,
                  InterruptedException
        Description copied from interface: BasePipe
        Performs pre-processing prior to item flow throw the pipe. Implementations must call the same method for all their input pipes before accessing their items. This is typically done here.
        Specified by:
        start in interface BasePipe
        Throws:
        PipeException - In case of pipe errors in this pipe or somewhere up-stream.
        InterruptedException - In case that the operation has been interrupted by another thread.

      • getProgress

        public float getProgress()
        Specified by:
        getProgress in interface BasePipe
        Returns:
        The pipe flow progress, as a floating number between 0.0 and 1.0. Important implementation rules: 1) Calling this method before start() call is complete isn't allowed and has an undefined behavior. 2) Implementation should do best effort to provide an estimate of the progress this pipe has made (0.0 - 1.0) 3) When the pipe is fully consumed, getProgress() should return 1.0. 4) Results must be monotonous, i.e. results of consecutive calls may never be decreasing. 5) Thread safety: progress may be maintained by some thread/s but monitoring by other threads. Implementations must be thread safe.

      • next

        public T next()
       throws PipeException,
              InterruptedException
        Specified by:
        next in interface Pipe<T>
        Returns:
        The next item in this pipe output, or null if the output end has been reached. May be a blocking operation.
        Throws:
        PipeException - In case of pipe errors in this pipe or somewhere up-stream while trying to prepare next item to return.
        InterruptedException - In case that the operation has been interrupted by another thread.

      • peek

        public T peek()
       throws PipeException
        Specified by:
        peek in interface Pipe<T>
        Returns:
        The next item in the pipe's output. Does not remove it, so next call to next() will return it.
        Throws:
        PipeException - In case of pipe errors in this pipe or somewhere up-stream while trying to prepare next item to return.