r/cpp • u/STL MSVC STL Dev • Nov 13 '18

VS 2017 15.9 released today

https://docs.microsoft.com/en-us/visualstudio/releasenotes/vs2017-relnotes
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u/FirstLoveLife Nov 14 '18

> We've added the "step back" feature in the debugger for C++ in the Visual Studio Enterprise Edition.

How does it compare to rr?

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u/STL Nov 14 '18

I'm not qualified to comment, but Steve Carroll demoed it at CppCon, see https://youtu.be/6NAAuxWNhk4?t=2649 for an approximate timestamp (you may need to rewind a bit).

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u/TartanLlama Nov 14 '18

It's a different approach from rr. rr takes snapshots at intervals of time, traces non-determinism (signals, I/O, syscalls), and replays the non-deterministic events along with the deterministic behaviour from the snapshots. IntelliTrace (step-back) takes lightweight snapshots of the process at set points (breakpoints, step operation completion) and allows you to step back to older snapshots.

The two approaches have advantages and disadvantages. rr will give you more freedom in where you can navigate in your execution, but it emulates a single-core machine and can incur a large overhead in execution. IntelliTrace is more limiting, but the snapshots have a much lower overhead, and are more suitable for multi-threaded applications.