The only time that the 'Work in Progress - Stop' button is displayed is when NX KNOWS that it's safe to halt an operation while not aborting the NX session. Until recently, that was only when whatever was happening didn't involve Parasolid updating the model or data was not being written to the disk, which was almost never. However, you can now halt NX, at least when working in Modeling, almost anytime except when filing data to the disk (that will always be an issue). Unfortunately I don't think we've ever given users control over this when creating their own applications using NX Open. Knowing when it's safe to interrupt an operation is a very complex issue and must take many things into consideration. Now there was a time, back before Unigraphics V10.0, almost 25 years ago, we had a universal 'halt' command, just hold down the 'Ctrl', 'Shift' and the 'L' key all at once and UG would literally stop in it's tracks, and almost never result in any sort of problems. But then that was back when you could only have a single part file open in one session of UG, there was no Parasolid kernel doing most of the modeling operations, there was no associative relationships between part files, etc. All in all, it was a much simpler life, for everyone including BOTH UG users AND UG developers.
Anyway, if you see, while running normal NX, the 'Work in Progress - Stop' button, it's safe to halt whatever NX was doing, but as I said, only the system itself is able to know when it would be safe to do so.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
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UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.