1 / 32

Threads II

Threads II. IS 313 5.15.2003. Outline. Quiz Thread review Stopping a thread java.util.Timer Swing threads javax.swing.Timer ProgressMonitor invokeLater. Thread Review I. Threads Java objects Independent paths of execution Share memory and code To define a thread’s behavior run().

davidcornett
Download Presentation

Threads II

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Threads II IS 313 5.15.2003

  2. Outline • Quiz • Thread review • Stopping a thread • java.util.Timer • Swing threads • javax.swing.Timer • ProgressMonitor • invokeLater

  3. Thread Review I • Threads • Java objects • Independent paths of execution • Share memory and code • To define a thread’s behavior • run()

  4. 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 run

  5. Thread 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()

  6. Thread Review IV

  7. Thread 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 unlocked

  8. How to stop a thread • run starts a thread • end of run method terminates • what if I want to stop thread sooner? • Answer • it depends

  9. Why not stop() • Existing method in thread API • Answer • Dead thread drops its locks • synchronized method may be only partially executed • corrupt state

  10. Example public void run () { while (true) { ... do something ... } }

  11. 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 ... } }

  12. To Stop the Thread thread.setRunning (false)

  13. Requirements • Inner loop • Exit variable checked regularly

  14. Alternative II (interrupt) public void run () { try { while (true) { foo.wait(); ... do something ... } } catch (InterruptedException e) { .. clean up ... } }

  15. To Stop the Thread thread.interrupt ();

  16. Requirements • Thread is in “wait” state in its inner loop • Also works for “sleep”

  17. Alternative III (i/o) public void run () { try { while (true) { byte [] buffer = inputStream.readBytes(4000); ... do something ... } } catch (IOException e) { .. clean up ... } }

  18. To Stop the Thread inputStream.close();

  19. Requirement • Thread is waiting for I/O in its inner loop

  20. Three 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 IOException

  21. Periodic 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 repeats

  22. java.util.Timer • Timer • schedule (TimerTask, delay) • schedule (TimerTask, delay, period) • TimerTask • implements Runnable

  23. java.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()

  24. javax.swing.Timer • Timer • Timer (delay, ActionListener) • ActionListener • actionPerformed (ActionEvent)

  25. 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.stop

  26. Progress Monitoring

  27. Example • Add progress monitor to a process • What needs to happen? • ProgressMonitor dialog must open • Monitor must be updated • Cancel/Completion must be handled

  28. ProgressMonitor class • ProgressMonitor(Component parentComponent, Object message, String note, int min, int max) • setProgress • tell the dialog to change progress indication

  29. Example

  30. Note • Updating must happen in EH thread • Swing timer ensures this • If updating from another thread • must place updates into the EH thread

  31. Interaction 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”

  32. 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 useful

More Related