[exporterhelper] fix missed metric aggregations (open-telemetry#9048)

This PR ensures that context cancellation in the exporter doesn't
interfere with metric aggregation. The OTel SDK currently returns if
there's an error in the context used in `Add` (see
https://github.com/open-telemetry/opentelemetry-go/blob/6cee2b4a4c76b581115d0d0ca150ad8b2e683db6/sdk/metric/instrument.go#L241-L243).
This means that if there's a cancelled context in an export, the metrics
are not recorded.

---------

Signed-off-by: Alex Boten <aboten@lightstep.com>

.chloggen/codeboten_fix-missing-metrics.yaml

@@ -0,0 +1,28 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: exporterhelper
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: fix missed metric aggregations
+
+# One or more tracking issues or pull requests related to the change
+issues: [9048]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: |
+  This ensures that context cancellation in the exporter doesn't interfere with metric aggregation. The OTel
+  SDK currently returns if there's an error in the context used in `Add`. This means that if there's a
+  cancelled context in an export, the metrics are now recorded.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

exporter/exporterhelper/obsexporter.go

@@ -154,7 +154,7 @@ func (or *ObsReport) StartTracesOp(ctx context.Context) context.Context {
 // EndTracesOp completes the export operation that was started with StartTracesOp.
 func (or *ObsReport) EndTracesOp(ctx context.Context, numSpans int, err error) {
 	numSent, numFailedToSend := toNumItems(numSpans, err)
-	or.recordMetrics(ctx, component.DataTypeTraces, numSent, numFailedToSend)
+	or.recordMetrics(noCancellationContext{Context: ctx}, component.DataTypeTraces, numSent, numFailedToSend)
 	endSpan(ctx, err, numSent, numFailedToSend, obsmetrics.SentSpansKey, obsmetrics.FailedToSendSpansKey)
 }
 
@@ -169,7 +169,7 @@ func (or *ObsReport) StartMetricsOp(ctx context.Context) context.Context {
 // StartMetricsOp.
 func (or *ObsReport) EndMetricsOp(ctx context.Context, numMetricPoints int, err error) {
 	numSent, numFailedToSend := toNumItems(numMetricPoints, err)
-	or.recordMetrics(ctx, component.DataTypeMetrics, numSent, numFailedToSend)
+	or.recordMetrics(noCancellationContext{Context: ctx}, component.DataTypeMetrics, numSent, numFailedToSend)
 	endSpan(ctx, err, numSent, numFailedToSend, obsmetrics.SentMetricPointsKey, obsmetrics.FailedToSendMetricPointsKey)
 }
 
@@ -183,7 +183,7 @@ func (or *ObsReport) StartLogsOp(ctx context.Context) context.Context {
 // EndLogsOp completes the export operation that was started with StartLogsOp.
 func (or *ObsReport) EndLogsOp(ctx context.Context, numLogRecords int, err error) {
 	numSent, numFailedToSend := toNumItems(numLogRecords, err)
-	or.recordMetrics(ctx, component.DataTypeLogs, numSent, numFailedToSend)
+	or.recordMetrics(noCancellationContext{Context: ctx}, component.DataTypeLogs, numSent, numFailedToSend)
 	endSpan(ctx, err, numSent, numFailedToSend, obsmetrics.SentLogRecordsKey, obsmetrics.FailedToSendLogRecordsKey)
 }