PipeReader.java

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package com.buglabs.bug.bmi;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;

import org.apache.commons.io.IOUtils;
import org.osgi.service.log.LogService;

/**
 * This class listens to a pipe for events from Hotplug. These events are passed
 * to the BMIManager.
 * 
 * @author kgilmer
 * 
 */
public class PipeReader extends Thread {
	/**
	 * Special input message that will cause the reader Thread to shutdown.
	 */
	private static final String POISON_PILL = "exit\n";

	private volatile FileInputStream stream = null;

	private final String pipeFilename;

	private final BMIModuleEventHandler eventHandler;

	private final LogService logService;

	/**
	 * @param pipeFilename
	 *            absolute path to pipe file
	 * @param eventHandler
	 *            reference to event handler
	 * @param logService
	 *            reference to log service
	 */
	public PipeReader(String pipeFilename, BMIModuleEventHandler eventHandler, LogService logService) {
		this.pipeFilename = pipeFilename;
		this.eventHandler = eventHandler;
		this.logService = logService;
	}

	/**
	 * Shutdown reader thread.
	 */
	public void shutdown() {

		try {
			FileOutputStream fos = new FileOutputStream(pipeFilename);
			IOUtils.write(POISON_PILL, fos);
			IOUtils.closeQuietly(fos);			
		} catch (IOException e) {
		}
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Thread#run()
	 */
	public void run() {
		logService.log(LogService.LOG_INFO, "Listening to event pipe. " + pipeFilename);
		while (!Thread.currentThread().isInterrupted()) {
			try {

				BufferedReader reader = new BufferedReader(new FileReader(pipeFilename));
				String line = null;
				String lastEvent = "";
				
				while ((line = reader.readLine()) != null) {
					if (line.equals(POISON_PILL)) {
						return;
					}
					
					if (line.equals(lastEvent)) {
						logService.log(LogService.LOG_DEBUG
								, "Squelching duplicate event.");
						continue;
					} 
					
					if (logService != null) {
						logService.log(LogService.LOG_DEBUG
								, "Received message from event pipe: " + line);
					}
					
					try {
						BMIModuleEvent m = new BMIModuleEvent(line);
						eventHandler.handleEvent(m);
					} catch (IOException e) {
						logService.log(LogService.LOG_ERROR
								, "Unable to parse message from event pipe: " + line);
					}
					lastEvent = line;
				}
			} catch (FileNotFoundException e) {
				logService.log(LogService.LOG_ERROR, e.getMessage());
			} catch (IOException e) {
				logService.log(LogService.LOG_ERROR, e.getMessage());
			} finally {
				IOUtils.closeQuietly(stream);				
			}
		}
	}
}