Right, that all makes sense. However, curiosity prevails...

The fact that there are no mentions anywhere in any of the NDK docs about 
progressFraction being unsafe to use in engine calls has me thinking it may be 
possible that the Op interface is handling message and progress handoffs to 
Nuke transparently to avoid these sorts of issues. I guess what I’m getting at 
is that maybe it’s not the Op::engine call itself that updates the interface, 
but rather it simply provides information that the GUI thread can choose to 
make use of.

Also, many of the sample Writer-derived classes use progressFraction fairly 
liberally in their execute() calls, and while I know these are probably 
single-threaded, I would venture to guess they aren’t running in the GUI thread 
either.

-Nathan



From: Steven Booth 
Sent: Tuesday, November 29, 2011 11:35 AM
To: Nuke plug-in development discussion 
Subject: RE: [Nuke-dev] Re: progressFraction bar not showing

It is never acceptable to update a UI from any thread other than the one that 
created it, which is almost always the ‘main’ or ‘primary’ thread.  Nuke spawns 
separate, dependent threads for all engine calls, and as such, updating any UI 
element from inside an engine call is an undefined operation.  The _validate, 
_open, _close, _invalidate, and knobs function calls are all executed in the 
main thread, and are UI-safe.

 

This, in fact, is a major problem for many Nuke developers that want to 
manipulate the display as a part of processing.  The only way to do it properly 
is to save state changes in a module-global variable inside your engine call, 
and then use the new values to update the UI in either _close or _invalidate.

 

It’s not a question of engine being thread-safe – it is – rather, it’s a 
question of the UI elements being thread-safe, which is not guaranteed.  

 

Steve

 

 

From: [email protected] 
[mailto:[email protected]] On Behalf Of Nathan Rusch
Sent: Tuesday, November 29, 2011 10:51 AM
To: [email protected]
Subject: Re: [Nuke-dev] Re: progressFraction bar not showing

 

Can you elaborate on this at all? I’m calling progressFraction in a plugin’s 
engine method with zero crashes, but while calling it, my engine is locked to a 
single thread... do you mean these functions aren’t thread-safe? Or are you 
talking about other UI update calls?

 

-Nathan

 

From: Steve3D 

Sent: Tuesday, November 29, 2011 7:41 AM

To: [email protected] 

Subject: [Nuke-dev] Re: progressFraction bar not showing

 

I hope you're not trying to update the UI from inside an 'engine' thread, 
because that's not allowed, and if it works, it will work intermittently and 
cause crashes.


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