On 27 Apr 2011, at 18:39, kxng wrote: > Hello, > > I have a question that is not really about fltk, but hope to get some helps > or approaches from here. > > My program has two child threads, thread1 and thread2 spawned from the main > thread. when a button from the main thread is clicked, it checks user's > selections on three check boxes. The checks can be in any combination, but > they always be executed in sequence. > > Thread1 is in charge of running three heavy calculations and thread2 is in > charge of displaying results immediately after each calculation to the GUI. I > have both threads created in main in the suspended states. When the button is > clicked, thread1 starts doing his jobs. Once thread1 finishes his first job, > it resumes thread2 to update the results to the screen. In the mean while, > thread2 continues to do his second job. > > The question I have is how do I put thread2 to pause until thread1 finishes > his second job, then thread2 can update the results to screen, then continue > one in this fashion. I do not want to use busy wait loop, because it will eat > up lots of cpu time. What is the best approach here in this case? > > Moreover, once thread1 finishes all his tasks, user can input different > parameters and restart the calculation again with different selections. > > > My test code is as followed:
Your test code is Windows specific, so I can't test it (you can easily wrap Windows and Posix threads in wrappers to make your code portable, BTW) but my observations are: - I'm not even sure you need the second thread, it is quite likely that what it is doing could be better done by having thread1 trigger callbacks in the main thread via the; int Fl::awake (Fl_Awake_Handler func, void *data = 0); method. This allows you to set a callback (executed in the main thread) to do the display updates etc as appropriate. So thread1 can the trigger those updates as required, and the updates themselves effectively happen in the primary thread, thereby simplifying locking and so forth, and essentially removing any chance of problems with updating the GUI form a subsidiary thread. - If you are dead-set on using a second thread, then you probably need to look at using some form of mutex to allow thread2 to block until thread1 signals that data is ready. Repeatedly suspending and resuming threads is seldom a good idea and is fraught with problems - simply having thread2 block until there is something to do is far more likley to be robust. Under Windows, you can do this in a number of ways, e.g. with a mutex or a semaphore - though in this case a simple notification event object might be the simplest. Have a brows around on MSDN, particularly the "Using Synchronization" pages, and there are loads of examples in there to show you things to try. _______________________________________________ fltk mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk
