labath wrote:
> Can we build this feature into the Progress class by calling an accessor?
> Something like:
>
> ```
> Progress progress("Manually indexing DWARF", module_desc.GetData(),
> total_progress);
> progress.SetMinimumNotificationTime(std::chrono::milliseconds(10));
> ```
>
> Then any busy progress dialogs can take advantage of this timing feature?
That's possible, but there are a couple of caveats:
- in the Progress class implementation, we'd only have a single "time of last
progress report" member, which would mean that (in order for it to be
lock-free) it would have to be atomic. As there's no `atomic<duration>`, this
would have to be a raw "time since epoch") timestamp. It's fine, but slightly
uglier, and it's also one more atomic. In this version I was able to get away
with it by essentially making the timestamp thread-local, which is sort of
nice, but also less correct than the hypothetical version with a single
variable, so maybe that's okay..
- this implementation only works if the progress updates come at a fairly fast
and steady rate. This is the case here, but may not be true for all usages.
With this implementation, if you have something that tries to send e.g. 9 (out
of 10) progress updates very quickly (within the 10ms interval), but then gets
spends a lot of time (many seconds) on the last part, the progress bar will
stay stuck at `1/10 ` because we've ignored the updates 2--9. Attempting to
schedule some sort of to send the `9/10` event after a timeout would probably
involve spinning up another thread, and all of this management would make the
code significantly more complicated (and slower).
This is the reason I did not want to make this a general feature, but it's not
strong opinion, so if you're find with these trade-offs, I can move the code
into the Progress class. I definitely don't want get into the business of
managing another thread though.
https://github.com/llvm/llvm-project/pull/118953
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