[news.eclipse.platform.swt] Re: aSyncExec behavior

[wegener@xxxxxxxxxxxxxx (Dave Wegener)]

Spencer Stejskal wrote:

> does Display.aSyncExec(Runnable) only run its runnable when the display 
> thread returns to the event loop?

> more specifically if the spawned thread below in the nonBlockingMethod gets 
> to LINE Y before the display thread gets to LINE X is the potential there 
> for the
> display thread to run the runnable in the asyncExec call before the display 
> thead finishes the someMethod invocation or will it wait until its back into 
> the display loop?

There is only one event loop thread per Display.  The thread can only be 
processing one event at a time.  If the event loop thread has called your 
someMethod() method like your comments indicate, it can't get to any other 
events until after your someMethod() returns.  This means that the event 
loop can't process the Runnable you create in line Y until after your 
someMethod() returns.


> private class SomeClass
> {
>         private List list = new ArrayList();

>         public void someMethod()
>         {
>                 long pid = nonBlockingMethod(display); {called from the 
> display thread, dont worry about where the display is retrieved from}
>                 //do some more work, maybe long maybe short
> LINE X   list.add(pid);
>         }

>         private long nonBlockingMethod(final Display display)
>         {
>                 long pid = generatePID();
>                 Thread t = new Thread(new Runnable(){
>                             public void run()
>                             {
>                                     //do some work, maybe long maybe short
> LINE Y                       display.asyncExec(new Runnable(){
>                                                 public void run()
>                                                 {
>                                                 if(list.contains(pid))
>                                                             {
>                                                                         //do 
> one thing
>                                                             }
>                                                             else
>                                                             {
>                                                                        //do 
> another thing
>                                                             }
>                                                 }
>                                     });
>                             }
>                     });
>                     t.start();
>                     return pid;
>         }
> }