Use PeriodicReader timeout for ForceFlush (#4377)

* Use PeriodicReader timeout for ForceFlush

Prioritize the user passed context deadline if it has one.

* Update changelog

CHANGELOG.md

@@ -37,7 +37,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - If an attribute set is Observed multiple times in an async callback, the values will be summed instead of the last observation winning. (#4289)
 - Allow the explicit bucket histogram aggregation to be used for the up-down counter, observable counter, observable up-down counter, and observable gauge in the `go.opentelemetry.io/otel/sdk/metric` package. (#4332)
 - Restrict `Meter`s in `go.opentelemetry.io/otel/sdk/metric` to only register and collect instruments it created. (#4333)
-- `PeriodicReader.Shutdown` in `go.opentelemetry.io/otel/sdk/metric` now applies the periodic reader's timeout by default. (#4356)
+- `PeriodicReader.Shutdown` and `PeriodicReader.ForceFlush` in `go.opentelemetry.io/otel/sdk/metric` now apply the periodic reader's timeout to the operation if the user provided context does not contain a deadline. (#4356, #4377)
 
 ### Fixed
 

sdk/metric/periodic_reader.go

@@ -68,7 +68,9 @@ func (o periodicReaderOptionFunc) applyPeriodic(conf periodicReaderConfig) perio
 
 // WithTimeout configures the time a PeriodicReader waits for an export to
 // complete before canceling it. This includes an export which occurs as part
-// of Shutdown.
+// of Shutdown or ForceFlush if the user passed context does not have a
+// deadline. If the user passed context does have a deadline, it will be used
+// instead.
 //
 // This option overrides any value set for the
 // OTEL_METRIC_EXPORT_TIMEOUT environment variable.
@@ -298,6 +300,13 @@ func (r *PeriodicReader) export(ctx context.Context, m *metricdata.ResourceMetri
 //
 // This method is safe to call concurrently.
 func (r *PeriodicReader) ForceFlush(ctx context.Context) error {
+	// Prioritize the ctx timeout if it is set.
+	if _, ok := ctx.Deadline(); !ok {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithTimeout(ctx, r.timeout)
+		defer cancel()
+	}
+
 	errCh := make(chan error, 1)
 	select {
 	case r.flushCh <- errCh:
@@ -324,8 +333,13 @@ func (r *PeriodicReader) ForceFlush(ctx context.Context) error {
 func (r *PeriodicReader) Shutdown(ctx context.Context) error {
 	err := ErrReaderShutdown
 	r.shutdownOnce.Do(func() {
-		ctx, cancel := context.WithTimeout(ctx, r.timeout)
-		defer cancel()
+		// Prioritize the ctx timeout if it is set.
+		if _, ok := ctx.Deadline(); !ok {
+			var cancel context.CancelFunc
+			ctx, cancel = context.WithTimeout(ctx, r.timeout)
+			defer cancel()
+		}
+
 		// Stop the run loop.
 		r.cancel()
 		<-r.done