Tohuwabohu excorcism

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−Table of Contents

Multithreading

Multithreading

What	Where
Introduction	vogella
Whereever possible use the safe Structures from	concurrent package

PitFalls

Do not use TimeStamps to synchronize Threads. Therere can be more than 1 action every millisecond - what to do with equal TimeStamps?

Concurrent Package

Das Concurrent Package bietet viele fertige Multithreading Klassen.

Class	What
Timer	Can execute TimerTasks(Runnables) after a Timeout. Can be canceled only once.
Future	Can compute something asynchronously. The result, when ready, is available throught get()

ForkJoin

A framework to execute parallel task. The mechanism is described here.

Display.readAndDispatch()

        
              //A nice way to stop the UI thread, in order to wait for a job, without blocking the UI Jobs coming from other Threads
while(job.getResult()==null) {
  Display.getDefault().readAndDispatch();
}

Try-Catch is Bypassed in nested threads

On every thread there should be an own Exception-handling. Putting a new Thread creation into try-catch block won't catch the Exceptions.

        
              //ATTENTION: the exception is not catched!
try{
    Runnable r = new Runnable() {
                 
        @Override
        public void run() {
            System.out.println("Thread");
                     
            Display.getDefault().syncExec(new Runnable() {
                   @Override
                   public void run() {
                    System.out.println("ThreadGUI");
                    throw new NullPointerException();
                   }
               });
                     
        }
    };
             
    Thread t = new Thread(r);
    t.start();
 
}catch(NullPointerException e){
    //nothing
}
         
System.out.println("Ende");