Package org.pipecraft.pipes.terminal

Class QueueWriterPipe<T>

java.lang.Object

org.pipecraft.pipes.terminal.TerminalPipe

org.pipecraft.pipes.terminal.QueueWriterPipe<T>

Type Parameters:

T - the queue item data type

All Implemented Interfaces:

Closeable, AutoCloseable, BasePipe

public class QueueWriterPipe<T>
extends TerminalPipe

A terminal pipe writing items to 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 consumer. Note that this pipe can cause a deadlock if not used properly. Calling start() will start pushing to the queue in a blocking manner, meaning that the consumer should be a different thread (or alternatively the queue should not be bounded, which is memory risky).

Author:

Eyal Schneider

Constructor Summary

Constructors

Constructor	Description
QueueWriterPipe(Pipe<T> inputPipe, BlockingQueue<T> queue, T successMarker, T errorMarker)	Constructor

Method Summary

Modifier and Type	Method	Description
void	close()
float	getProgress()
void	start()	Performs pre-processing prior to item flow throw the pipe.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

QueueWriterPipe

public QueueWriterPipe(Pipe<T> inputPipe,
                       BlockingQueue<T> queue,
                       T successMarker,
                       T errorMarker)

Constructor

Parameters:

inputPipe - The pipe to read items from and push them to the queue

queue - The queue to write to

successMarker - Used for indicating data completion with success. Should be a unique reference reserved for this purpose. Consumer should use the same marker reference for end of input indication.

errorMarker - Used for indicating an error termination. Should be a unique reference reserved for this purpose. Consumer should use the same marker reference for error indication.

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.

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

Overrides:

getProgress in class TerminalPipe

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.

close

public void close()
           throws IOException

Throws:

IOException