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Fixes #629

managed to crash it.

Give this sequence:

    Meter = opentelemetry_experimental:get_meter(),
    true = otel_meter_server:add_view(
             #{instrument_kind => ?KIND_HISTOGRAM},
             #{aggregation_module => otel_aggregation_histogram_explicit,
               aggregation_options => #{boundaries => [10, 100]}}),
    Histogram = otel_histogram:create(Meter, histogram, #{}),
    true = otel_meter_server:add_view(
             #{instrument_name => histogram},
             #{
               aggregation_module => otel_aggregation_histogram_explicit,
               aggregation_options => #{boundaries => [10, 20, 30, 40, 50, 60, 70, 80, 100]}}),
    ok = otel_histogram:record(Histogram, 2000, #{<<"a">> => <<"1">>})

It will crash with:

{badarg,
    [{counters,add,
         [{write_concurrency,#Ref<0.388515526.2174353409.18119>},10,1],
         [{error_info,#{module => erl_erts_errors}}]},
     {otel_aggregation_histogram_explicit,aggregate,4,
         [{file,
              "/usr/src/erlang/opentelemetry-erlang/apps/opentelemetry_experimental/src/otel_aggregation_histogram_explicit.erl"},
          {line,175}]},
     {otel_aggregation,maybe_init_aggregate,4,
         [{file,
              "/usr/src/erlang/opentelemetry-erlang/apps/opentelemetry_experimental/src/otel_aggregation.erl"},
          {line,49}]},

Root problem is that the the second view does not update the counter bucket in the histogram view.

There is nothing in the OpenTelemetry specification that indicates that doing something like that is not permitted.
Even the code suggest that it should be fine to update views like that. Of course, I would expect that such an updated flushes any already collected data points.

Thanks, I will look at it

We likely don't want to support updating views -- I don't think any implementation does. But also don't want to crash :)

There has been talk about this in the metrics SIG, about whether you can even add views after the meter provider has started or not.

We do not handle very well duplicated metrics, see https://opentelemetry.io/docs/specs/otel/metrics/sdk/#measurement-processing. In the case of the example you provided we are defining a duplicated metric with different boundaries, it is not exactly what is written in the spec but I think we should drop the second view

@tsloughter ready