StreamGobbler.java

/*******************************************************************************
 * Copyright (c) 2006 IBM Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - Jeff Briggs, Henry Hughes, Ryan Morse
 *******************************************************************************/

package org.eclipse.linuxtools.systemtap.structures.runnable;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.eclipse.linuxtools.systemtap.structures.listeners.IGobblerListener;

/**
 * A separate thread to listen to an InputStream and pull all the data
 * out of it. When data is found a new event is fired share the data with
 * any <code>IDataListener</code> that is listening.
 * @author Ryan Morse
 */
public class StreamGobbler implements Runnable {

    public StreamGobbler(InputStream is) {
        if(null != is) {
            this.is = is;
            line = new StringBuilder();
            listeners = new ArrayList<>();
        }
    }

    /**
     * Spawns the new thread that this class will run in.  From the Runnable
     * interface spawning the new thread automatically calls the run() method.
     * This must be called by the implementing class in order to start the
     * StreamGobbler.
     */
    //Make sure to call this method to start the StreamGobbler
    public void start() {
        reader = new Thread(this, "StreamGobbler"); //$NON-NLS-1$
        reader.start();
    }

    /**
     * Checks to see if the gobbler is still running.
     * @return boolean representing whether or not it is sill running
     */
    public boolean isRunning() {
        return (null != reader);
    }

    /**
     * The main method of this class. It monitors the provided thread to see
     * when new data is available and then appends it to its current list of
     * data.  When a new line is read it will fire a DataEvent for listeners
     * to get a hold of the data.
     */
    @Override
    public void run() {
        if (reader != Thread.currentThread())
            return;

        try {
            int val = is.read();
            while(val != -1) {
                line.append((char)val);

                if ('\n' == val)
                    this.fireNewDataEvent();

                val = is.read();
            }
        } catch (IOException ioe) {}    // If stream closed before thread shuts down
    }

    /**
     * Stops the gobbler from monitoring the stream, and fires one last data event
     * to make sure that listeners have the entire contents of what was read in
     * from the stream.
     */
    public synchronized void stop() {
        if (reader != null){
            try {
                // Wait for the reader thread to finish.
                reader.join();
            } catch (InterruptedException e) {
                // The thread was interrupted; nothing to do; finish stopping.
            }
            reader = null;
        }
        notify();
        // Fire one last time to ensure listeners have gotten everything.
        this.fireNewDataEvent();
    }

    /**
     * Gets rid of all internal references to objects.
     */
    public void dispose() {
        if(isRunning())
            stop();
        line = null;
        reader = null;
        is = null;
    }

    /**
     * Fires new events to everything that is monitoring this stream. Then clears
     * the current line of data.
     */
    private void fireNewDataEvent() {
        this.fireNewDataEvent(line.toString());
        line.delete(0, line.length());
    }

    public void fireNewDataEvent(String l) {
        synchronized (listeners) {
            for(int i = 0; i < listeners.size(); i++){
                listeners.get(i).handleDataEvent(l);
            }
        }
    }

    /**
     * Registers the provided listener to get data events.
     * @param l A listener that needs to monitor the stream.
     */
    public void addDataListener(IGobblerListener l) {
        synchronized (listeners) {
            if(l != null && !listeners.contains(l)){
                listeners.add(l);
            }
        }
    }

    /**
     * Unregisters the provided listener from getting new data events.
     * @param l A listener that is monitoring the stream and should be removed
     */
    public void removeDataListener(IGobblerListener l) {
        synchronized (listeners) {
            if(listeners.contains(l))
                listeners.remove(l);
        }
    }

    private List<IGobblerListener> listeners;
    private StringBuilder line;
    private Thread reader;
    private InputStream is;
}