[lldb] Add ability to rate-limit progress reports (#119377)

For high-frequency multithreaded progress reports, the contention of
taking the progress mutex and the overhead of generating event can
significantly slow down the operation whose progress we are reporting.

This patch adds an (optional) capability to rate-limit them. It's
optional because this approach has one drawback: if the progress
reporting has a pattern where it generates a burst of activity and then
blocks (without reporting anything) for a large amount of time, it can
appear as if less progress was made that it actually was (because we
only reported the first event from the burst and dropped the other
ones).

I've also made a small refactor of the Progress class to better
distinguish between const (don't need protection), atomic (are used on
the hot path) and other (need mutex protection) members.

0 files changed, 0 insertions, 0 deletions