===== Multithreading =====
^What ^Where ^
|Introduction | [[http://www.vogella.com/articles/JavaConcurrency/article.html|vogella]] |
|Whereever possible use the safe Structures from | [[http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/package-summary.html|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 [[http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/package-summary.html|Concurrent Package]] bietet viele fertige Multithreading Klassen.


^Class ^ What ^
| [[http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Timer.html|Timer]] | Can execute TimerTasks(Runnables) after a Timeout. Can be canceled only once. |
| [[http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/FutureTask.html|Future]]  | Can compute something asynchronously. The result, when ready, is available throught get() |


=== ForkJoin ===
A framework to execute parallel task. The mechanism is [[http://www.cs.washington.edu/homes/djg/teachingMaterials/spac/grossmanSPAC_forkJoinFramework.html|described here]].


[[http://help.eclipse.org/helios/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Freference%2Fapi%2Forg%2Feclipse%2Fswt%2Fwidgets%2FDisplay.html|Display.readAndDispatch()]]
<sxh java>
//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();
}
</sxh>

=== 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.

<sxh java>
		//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");
</sxh>