Provides the implementation of period-based scanning, as well * as Deployer integration. * *
Sub-classes only need to implement {@link DeploymentScanner#scan}. * * @version $Revision: 1.9.2.3 $ * @author Jason Dillon */ public abstract class AbstractDeploymentScanner extends ServiceMBeanSupport implements DeploymentScanner, DeploymentScannerMBean { /** The scan period in milliseconds */ protected MuLong scanPeriod = new MuLong(5000); /** True if period based scanning is enabled. */ protected MuBoolean scanEnabled = new MuBoolean(true); /** A proxy to the deployer we are using. */ protected Deployer deployer; /** The scanner thread. */ protected ScannerThread scannerThread; /** HACK: Shutdown hook to get around problems with system service shutdown ordering. */ private Thread shutdownHook; ///////////////////////////////////////////////////////////////////////// // DeploymentScanner // ///////////////////////////////////////////////////////////////////////// public void setDeployer(final ObjectName deployerName) { if (deployerName == null) throw new NullArgumentException("deployerName"); deployer = (Deployer) MBeanProxyExt.create(Deployer.class, deployerName, server); } public ObjectName getDeployer() { return ((MBeanProxyInstance)deployer).getMBeanProxyObjectName(); } /** * Period must be >= 0. */ public void setScanPeriod(final long period) { if (period < 0) throw new IllegalArgumentException("ScanPeriod must be >= 0; have: " + period); this.scanPeriod.set(period); } public long getScanPeriod() { return scanPeriod.longValue(); } public void setScanEnabled(final boolean flag) { this.scanEnabled.set(flag); } public boolean isScanEnabled() { return scanEnabled.get(); } /** This is here to work around a bug in the IBM vm that causes an * AbstractMethodError to be thrown when the ScannerThread calls scan. * @throws Exception */ public abstract void scan() throws Exception; ///////////////////////////////////////////////////////////////////////// // Scanner Thread // ///////////////////////////////////////////////////////////////////////// /** * Should use Timer/TimerTask instead? This has some issues with * interaction with ScanEnabled attribute. ScanEnabled works only * when starting/stopping. */ public class ScannerThread extends Thread { /** We get our own logger. */ protected Logger log = Logger.getLogger(ScannerThread.class); /** True if the scan loop should run. */ protected boolean enabled; /** True if we are shutting down. */ protected boolean shuttingDown; /** Lock/notify object. */ protected Object lock = new Object(); public ScannerThread(boolean enabled) { super("ScannerThread"); this.enabled = enabled; } public void setEnabled(boolean enabled) { this.enabled = enabled; synchronized (lock) { lock.notifyAll(); } if (log.isDebugEnabled()) { log.debug("Notified that enabled: " + enabled); } } public void shutdown() { enabled = false; shuttingDown = true; synchronized (lock) { lock.notifyAll(); } if (log.isDebugEnabled()) { log.debug("Notified to shutdown"); } // jason: shall we also interrupt this thread? } public void run() { log.info("Running"); while (!shuttingDown) { // If we are not enabled, then wait if (!enabled) { try { log.debug("Disabled, waiting for notification"); synchronized (lock) { lock.wait(); } } catch (InterruptedException ignore) {} } loop(); } log.info("Shutdown"); } public void doScan() { // Scan for new/removed/changed/whatever try { scan(); } catch (Exception e) { log.error("Scanning failed; continuing", e); } } protected void loop() { while (enabled) { doScan(); // Sleep for scan period try { log.trace("Sleeping..."); Thread.sleep(scanPeriod.longValue()); } catch (InterruptedException ignore) {} } } } ///////////////////////////////////////////////////////////////////////// // Service/ServiceMBeanSupport // ///////////////////////////////////////////////////////////////////////// protected void createService() throws Exception { if (deployer == null) throw new MissingAttributeException("Deployer"); // setup + start scanner thread scannerThread = new ScannerThread(false); scannerThread.setDaemon(true); scannerThread.start(); log.debug("Scanner thread started"); // HACK // // install a shutdown hook, as the current system service shutdown // mechanism will not call this until all other services have stopped. // we need to know soon, so we can stop scanning to try to avoid // starting new services when shutting down final ScannerThread _scannerThread = scannerThread; shutdownHook = new Thread("DeploymentScanner Shutdown Hook") { ScannerThread scannerThread = _scannerThread; public void run() { scannerThread.shutdown(); } }; try { Runtime.getRuntime().addShutdownHook(shutdownHook); } catch (Exception e) { log.warn("Failed to add shutdown hook", e); } } protected void startService() throws Exception { synchronized( scannerThread ) { // scan before we enable the thread, so JBoss version shows up afterwards scannerThread.doScan(); // enable scanner thread if we are enabled scannerThread.setEnabled(scanEnabled.get()); } } protected void stopService() throws Exception { // disable scanner thread if( scannerThread != null ) scannerThread.setEnabled(false); } protected void destroyService() throws Exception { // drop our ref to deployer, so scan will fail deployer = null; // shutdown scanner thread synchronized( scannerThread ) { scannerThread.shutdown(); } // HACK // // remove the shutdown hook, we don't need it anymore try { Runtime.getRuntime().removeShutdownHook(shutdownHook); } catch (Exception ignore) { } // who cares really // help gc shutdownHook = null; scannerThread = null; } }