uk.ac.starlink.util
Class PipeReaderThread

java.lang.Object
  extended by java.lang.Thread
      extended by uk.ac.starlink.util.PipeReaderThread
All Implemented Interfaces:
Runnable

public abstract class PipeReaderThread
extends Thread

Thread which reads data from a pipe. Having got an instance of this class, you can call its getOutputStream method to acquire a stream to write into, and then implement its doReading(java.io.InputStream) method to process the data; this method runs in the new thread.

Here is an example of using the class to count the bytes written down a stream:

     PipeReaderThread reader = new PipeReaderThread() {
        protected void doReading( InputStream dataIn ) throws IOException {
            int i;
            while ( dataIn.read() >= 0 ) i++;
            System.out.println( i );
        }
     };
     reader.start();
     OutputStream dataOut = reader.getOutputStream();
     // write bytes down dataOut ...
     dataOut.close();
     reader.finishReading();
 
Other uses will look pretty similar, but just override doReading in different ways. Note that any exceptions thrown by doReading are caught and eventually thrown in the reader thread by finishReading. The same exception may also be thrown by the write method of the writer thread.

This class serves two purposes. Firstly it copes with IOExceptions encountered during the read, and makes sure they get thrown at the writing end of the pipe (doReading is declared to throw IOException). Secondly it shields the user from the implementation of the piped connection. Performance of the PipedInputStream/PipedOutputStream is dismal - this class may be able to do better.

The current implementation uses a couple of drop-in Piped*Stream replacements, but performance still isn't great - it may be possible to do better in future. You can provide your own paired pipes by overriding both getInputStream() and getOutputStream().


Nested Class Summary
 
Nested classes/interfaces inherited from class java.lang.Thread
Thread.State, Thread.UncaughtExceptionHandler
 
Field Summary
 
Fields inherited from class java.lang.Thread
MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY
 
Constructor Summary
PipeReaderThread()
          Constructs a new reader thread.
 
Method Summary
protected abstract  void doReading(InputStream dataIn)
          This method should be implemented to consume all the bytes in the given input stream.
 void finishReading()
          Waits until the doReading method has finished reading the bytes written down the output stream, and returns.
protected  InputStream getInputStream()
          Returns the stream at the input end of the pipe.
 OutputStream getOutputStream()
          Returns the stream at the output end of the pipe.
 void run()
          Implements the thread's run method to invoke doReading, catching and saving IOExceptions.
 
Methods inherited from class java.lang.Thread
activeCount, checkAccess, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

PipeReaderThread

public PipeReaderThread()
                 throws IOException
Constructs a new reader thread.

Throws:
IOException
Method Detail

getInputStream

protected InputStream getInputStream()
Returns the stream at the input end of the pipe.

Returns:
input stream

getOutputStream

public OutputStream getOutputStream()
Returns the stream at the output end of the pipe.

Returns:
output stream

run

public void run()
Implements the thread's run method to invoke doReading, catching and saving IOExceptions.

Specified by:
run in interface Runnable
Overrides:
run in class Thread

doReading

protected abstract void doReading(InputStream dataIn)
                           throws IOException
This method should be implemented to consume all the bytes in the given input stream. It is probably a good idea for implementations to buffer the supplied input stream for efficiency. Note that any implementation of this method which does not read dataIn to the end of the stream (either closing it early or just stopping reading) may cause an IOException to be thrown in the thread which is writing to the PipedOutputStream.

Parameters:
dataIn - stream which will supply bytes
Throws:
IOException - if any I/O error occurs; this exception will be saved and thrown later by the finishReading method

finishReading

public void finishReading()
                   throws IOException
Waits until the doReading method has finished reading the bytes written down the output stream, and returns. Any IOException which has occurred during the read will be thrown by this method.

Throws:
IOException

Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved.