Threads IIOutlineThread Review IThreads Review IIThread Review IIIThread Review IVThread Review VHow to stop a threadWhy not stop()ExampleAlternative I (exit variable)To Stop the ThreadRequirementsAlternative II (interrupt)To Stop the ThreadRequirementsAlternative III (i/o)To Stop the ThreadRequirementThree ways to stopPeriodic Actionjava.util.Timerjava.util.Timer Lifecyclejavax.swing.Timerjavax.swing.Timer LifecycleProgress MonitoringExampleProgressMonitor classExampleNoteInteraction between threads and UIAccessing the EH ThreadThreads IIIS 3135.15.2003Outline Quiz Thread review Stopping a thread java.util.Timer Swing threads javax.swing.Timer ProgressMonitor invokeLaterThread Review I Threads Java objects Independent paths of execution Share memory and code To define a thread’s behavior run()Threads Review II Threads only appear to run simultaneously only a single thread executes at a time each thread runs for a time and then is replaced by another Priority determines which available thread is allowed to runThread Review III Java event handling takes place in a single thread other system threads Threads may have resource conflict share the processor with sleep() and yield() achieve exclusive use through synchronized methods coordinate using wait() and notify()Thread Review IVThread Review V Lifecycle methods start = transition to runnable end of run method = transition to dead transition to non-runnable wait () sleep () blocked transition back to runnable notify () end of sleep resource unlockedHow to stop a thread run starts a thread end of run method terminates what if I want to stop thread sooner? Answer it dependsWhy not stop() Existing method in thread API Answer Dead thread drops its locks synchronized method may be only partially executed corrupt stateExamplepublic void run (){while (true){... do something ...}}Alternative I (exit variable)private boolean m_isRunning;public synchronized void setIsRunning (boolean newVal){ m_isRunning = newVal; }public synchronized boolean IsRunning (){ return m_isRunning; }public void run (){setIsRunning(true);while (isRunning()){ ... do something ... }}To Stop the Threadthread.setRunning (false)Requirements Inner loop Exit variable checked regularlyAlternative II (interrupt)public void run (){try{while (true){foo.wait();... do something ...}} catch (InterruptedException e){.. clean up ...}}To Stop the Threadthread.interrupt ();Requirements Thread is in “wait” state in its inner loop Also works for “sleep”Alternative III (i/o)public void run (){try{while (true){byte [] buffer = inputStream.readBytes(4000);... do something ...}} catch (IOException e){.. clean up ...}}To Stop the ThreadinputStream.close();Requirement Thread is waiting for I/O in its inner loopThree ways to stop Rapid inner loop use a loop exit variable Wait state call interrupt() use the interrupted exception Waiting on I/O close the I/O stream use the IOExceptionPeriodic Action Examples Check the mail server every 10 minutes Animate something on the screen Autosave Need a thread that sleeps for a specified period then runs possibly repeatsjava.util.Timer Timer schedule (TimerTask, delay) schedule (TimerTask, delay, period) TimerTask implements Runnablejava.util.Timer Lifecycle Timer created Task scheduled wait setup in Timer thread Time arrives TimerTask run method called (not a separate thread) Timer canceled timer.cancel()javax.swing.Timer Timer Timer (delay, ActionListener) ActionListener actionPerformed (ActionEvent)javax.swing.Timer Lifecycle ActionListener created Timer created Timer started timer.start() wait setup (in Timer thread) Time arrives actionEvent created and inserted in event queue ActionListener handles event Timer canceled timer.stopProgress MonitoringExample Add progress monitor to a process What needs to happen? ProgressMonitor dialog must open Monitor must be updated Cancel/Completion must be handledProgressMonitor class ProgressMonitor(Component parentComponent, Object message, String note, int min, int max)  setProgress tell the dialog to change progress indicationExampleNote Updating must happen in EH thread Swing timer ensures this If updating from another thread must place updates into the EH threadInteraction between threads and UI Swing components are not thread-safe methods not synchronized example Solution only modify components from with the EH thread after the component has been “realized”Accessing the EH Thread EventQueue.invokeLater (Runnable) What happens event inserted into event queue when it comes to top run method of object is called Also invokeAndWait(Runnable) not as