Explicitly define metric reader force flush operation

[legendecas]

Related: #2983
Related: open-telemetry/opentelemetry-js#3278

Changes

ForceFlush MUST invoke ForceFlush on all registered MetricReader and Push Metric Exporter instances.

The method MetricReader.ForceFlush is already mentioned in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#forceflush. However, the specification doesn't explicitly define the method MetricReader.ForceFlush.

This also suggests that ForceFlush of Periodic exporting MetricReader should call Collect to consume the metrics.

[reyang]

The method MetricReader.ForceFlush is already mentioned in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#forceflush. However, the specification doesn't explicitly define the method MetricReader.ForceFlush.

This also suggests that ForceFlush of Periodic exporting MetricReader should call Collect to consume the metrics.

Could this be fixed by changing:

ForceFlush MUST invoke ForceFlush on all registered MetricReader and Push Metric Exporter instances.

to:

ForceFlush MUST invoke Collect on all registered MetricReader and ForceFlush on all Push Metric Exporter instances.

[legendecas]

@reyang for pull metric reader, I don't think it is meaningful to invoke Collect on force flush, similar to pull metric exporter mentioned at https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#pull-metric-exporter.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[legendecas]

Not stale, friendly ping @reyang

[reyang]

Not stale, friendly ping @reyang

Hi @legendecas, what's expected from me?

[legendecas]

@reyang has your question #3084 (comment) been addressed with #3084 (comment)? If so, is this PR still looking good to you?

[reyang]

@reyang has your question #3084 (comment) been addressed with #3084 (comment)? If so, is this PR still looking good to you?

I didn't ask a question, in the comment I had a suggestion. With the change proposed by the current PR, I find it hard to understand what's the difference between MetricReader.Collect and MetricReader.ForceFlush.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[legendecas]

@reyang MetricReader.Collect can be initiated by external collectors like prometheus scraping. However, MetricReader.ForceFlush is intended for sdk to notify MetricReaders that they should consume and send as much metric as they can.

ForceFlush MUST invoke ForceFlush on all registered
MetricReader and Push Metric Exporter
instances.

The statement in the spec has already mentioned that SDK's ForceFlush should invoke MetricReader's ForceFlush. This change doesn't change this behavior.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.