Series start time

[jack-berg]

Adjusts timeseries start time behavior to match the spec: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#start-timestamps

This is a prerequisite to finishing / closing instruments, a long time feature request.

Currently:

• Delta sync and async series set the datapoint start time to be the time of the last collection, and the time of SdkMeterProvider initialization for the first collection
• Cumulative sync and async series set the datapoint start time to be the time SdkMeterProvider initialization

With this PR:

• Delta sync and async series set the datapoint start time to be the time of the last collection, and the time of instrument creation for first collection
• Cumulative
  • Sync series set the datapoint start time to be the time of the first measurement for the series
  • Asynchronous series set the datapoint start time to be the instrument creation time if the series was recorded in the first collection, otherwise, the timestamp of the collection preceding first measurement for the series

To accomplish this, I needed to:

• Stop tracking SdkMeterProvider initialization time via MeterProviderSharedState. This is no longer used in any case.
• Decompose AsynchronousMetricStorage into an abstract class with cumulative and delta implementations. This mirrors DefaultSynchronousMetricStorage, and facilitates the behavior differences based on temporality.
• Start tracking AggregationHandle creation time (i.e. the time a measurement was first observed for a series), since this is now needed in cumulative cases.
• Stop passing down startEpochNanos down the callstack when collecting. Instead, this is now computed by MetricStorage implementations based on sync / async and cumulative / delta combinations.

cc @atoulme, @dashpole

[codecov]

Codecov Report

❌ Patch coverage is 99.24812% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.30%. Comparing base (6edc786) to head (818eace).
⚠️ Report is 44 commits behind head on main.

Files with missing lines	Patch %	Lines
...rics/internal/state/AsynchronousMetricStorage.java	98.98%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8180      +/-   ##
============================================
+ Coverage     90.29%   90.30%   +0.01%     
+ Complexity     7652     7643       -9     
============================================
  Files           843      842       -1     
  Lines         23066    23099      +33     
  Branches       2310     2325      +15     
============================================
+ Hits          20827    20860      +33     
+ Misses         1520     1519       -1     
- Partials        719      720       +1     

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[dashpole]

this looks correct to me

[zeitlinger]

looks good - created jack-berg#23 for some small fixes

[jack-berg]

Thanks @zeitlinger! Merged.