[vtkusers] Moving an actor, after about 1.5 hours.

[Sean McBride]

Not necessarily.  vtkAtomicInt32 is signed, and signed overflow is undefined in C++.  So once the ++ operator overflows GlobalTimeStamp, all bets are off.

clang's UBSan could catch this at runtime:

<http://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html>

but I'm not sure if it works on Windows.

Sean



On Tue, 8 Mar 2016 06:47:16 -0700, David Gobbi said:

>Since only the low 32 bits are kept (the high bits are simply discarded),
>the wrap-around of the ModifiedTime is exactly the same as if a 32-bit
>unsigned integer was being incremented.
>
> - David
>
>On Tue, Mar 8, 2016 at 6:27 AM, Richard Frank <rickfrank at me.com> wrote:
>
>> Actually, it's a bit stranger than I thought. The global time stamp on
>> Windows 64 bit is a 64 bit int cast to an
>> Unsigned long, as size of void ptr is 8
>> void vtkTimeStamp::Modified()
>> {
>> #if VTK_SIZEOF_VOID_P == 8
>> static vtkAtomicInt64 GlobalTimeStamp(0);
>> #else
>> static vtkAtomicInt32 GlobalTimeStamp(0);
>> #endif
>> this->ModifiedTime = (unsigned long)++GlobalTimeStamp;
>> }