Class PipeReaderThread

java.lang.Object
java.lang.Thread
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(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().

Author:
Mark Taylor (Starlink)

  • Constructor Details

    • PipeReaderThread

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

  • Method Details

    • 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. Implementations should not close the supplied input stream.
      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, closes the input stream, and returns. Any IOException which has occurred during the read will be thrown by this method.
      Throws:
      InterruptedIOException - if failure was caused by interruption; the bytesTransferred field of this exception is not set to a useful value
      IOException - in case of some other IO failure

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