I don’t know if this affect other users, but most of times when the Scene Parsing and Geometry is running and you press Stop - it doesn’t STOP.
Is the most annoying thing in Corona, that when you press the Cancel button or Stop button, it doesn’t stop the render. It has to go until the end of the calculation to stop. So, must of the times we have to wait like 15 minutes or 20 minutes until we can start work. Is this a bug?
Just me then and another 10 guys? Could be a server problem?
its not the most annoying imo 
yes sometimes i need it when for example when I forgot to run the render without turn off the displacement, canceling the calculation is the right time to do something we forgot. and, uhm it looks like that scene parsing / geometry calculation isn’t designed to be interruptible.
Does anybody know is this behavior occurred in other renderer too?
and, if it is possible I’d like to have interruptible sceneParsing/geometryCalculation in corona.
15 - 20min seems to be a lot of time for coffee.
Computing sec. GI can be easily canceled so Parsing scene and preparing geometry should be too when corona team look on it 
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I am not sure about the first pass Transforming Verticles, probably it is handled completely by max, you can not even move VFB window during it. For example in this pass is Forest pack calculating all areas defined by splines. In my last project I was forced to do some optimization in number of spline verticles(I save lot of time during this pass!!).
I dont know how big are your scenes, can you also do some optimization so the waiting for canceling would be not so painful?
+1 for stop render during preprocessing
+1 for me too. Not sure if it’s a Max thing or not, but would love for instant cancel of any render stage when you hit Stop / Cancel
I had a similar problem on my previous system which was a lot slower and at about 16 gig ram
especially with large scenes
With my new workstation with 32 gig ram and overclocked i7 at 4.8 I have almost instantaneous cancellation of rendering
I always just thought it was a ram thing, or just a general slow system thing and not the render engine per se.
So glad I am not the only one. The most annoying thing. I said “Cancel” not finish the calculations.
@Christa Noel - from what I recall, on Vray and Mental Ray, if you press Stop it Stops. No matter what kind of calculations is doing.
@Jadefox - 128GB for a small scene isn’t enough? Yet, if you press stop it should stop no matter the RAM size
The only reason I can think of would be running out of RAM. System becoming non-responsive in general is a typical symptom.
I had this situation where Corona would not react to stop/cancel buttons only once, and never managed to reproduce it again.
If it ever happens to anyone, and it is not caused by running out of RAM, it would be great if you could generate a minidump during the freeze and send it to us along with a report. Here is how to do it: https://coronarenderer.freshdesk.com/support/solutions/articles/5000524006-how-to-report-issues-
To make it clear what we think video: http://images.bzucko.sk/stopRender.mp4
Yeah, I think a minidump could let the devs see what is going on under the hood.
Also, are you using some 3rd party plugins like Forest Pack here? Just a random idea, but maybe worth a try - could you disable “multithreaded parsing” in devel/debug rollout and see if it changes anything?
Yes, I am using forest pack, lot of grass and trees. It is slightly worse with disabled multithreaded parsing, GUI is even less able to react. http://images.bzucko.sk/stopRender2.mp4
I created minidump during parsing scene using process explorer. http://images.bzucko.sk/stopRenderMiniDump.rar
It happens to me and to my co workers quite frequently. What is annoying is that Corona just keeps the calculation like you didn’t press the Cancel or Stop button. Only, after finishing the initial calculations it stops, but the system stills responds. This happens when the scene is complex, but even when isn’t I had the same issue.
Looks like something is wrong in mesh.dll, which is a part of 3ds Max, but probably someone from the dev team will be able to tell more.
The minidump is here: Stop Render - Corona for 3ds Max :: Issues - Chaos Forum