On 30 Sep 2020, at 17:49, anmol.mishra wrote:
> 
> Hi. I want to create a simple progress bar, and do not need any user input. I cannot block my main app as it already has its own GUI.
> What will happen if I use the following from a worker thread ?



> I read the docs, and its clear that the main thread owns the window, but if I dont care about user input, is there any harm in this ?


It’s not about user input - the issue is what process, and what thread within that process, owns the context that writes to the GPU...

Now, with more modern GPU drivers, and operating systems, that’s not as fragile as it once was, but basically the *safe* thing to do is handle GUI context from the main thread, always.

Trying to create windows from a subsidiary thread is likely to lead to trouble in strange and hard to debug ways...

However, the key here is that you do not need to call Fl::run() at all, if you only want to drive the GUI from your main thread: all you have to do is call Fl::wait(0); every now and then (say every 100ms or so if you just want to update the GUI but not handle user input...)

So if you can create and show all the window objects in your main thread, then arrange for Fl::wait() to be called periodically from the main thread, that ought to just about do the job.




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