Add feature for measuring duration of arbitrary code

[loganek]

Currently we have a scoped tracepoint, which allows us to measure an time of executing the code:

{
  ht_feature_callstack_start_string(timeline, "label");
  // some code
  ht_feature_callstack_start_string_stop(timeline);
}

Unfortunately we can't measure time of code which is overlapping; e.g. we can't measure time for code1+code2 and code2+code3 at the same time using the same timeline:

// code1
// code2
// code3

We should design and implement timeline feature, which would allow us to measure time of any code; something like:

HT_DurationId id1 = ht_feature_duration_start(timeline);
// code1
HT_DurationId id2 = ht_feature_duration_start(timeline);
// code2
HT_DurationNs duration1 = ht_feature_duration_stop(timeline, id1);
// code3
HT_DurationNs duration2 = ht_feature_duration_stop(timeline, id2);

[andrewrch]

I'm going to look in to this later today 👍

[loganek]

Hey @andrewrch any progress on that issue? :)

[andrewrch]

Hey 😊 I made a start on it on the train back on Tuesday. Started with the implementation of feature_callstack and worked from there. Getting some issues at the moment accessing events I put in a bag. Will spend a bit more time on it tonight/tomorrow and let you know if I need a hand.

[loganek]

Thanks for the update :) No rush, just wanted to know if you had a chance to look into this and if there's anything I could help you with.