Prometheus exporter no longer collects metrics after shutdown (#4648)

* prometheus exporter no longer collects metrics after shutdown

* use errors.Is

CHANGELOG.md

@@ -45,6 +45,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` does no longer depend on `go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#4660)
 - `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp` does no longer depend on `go.opentelemetry.io/otel/exporters/otlp/otlpmetric`. (#4660)
 
+### Fixed
+
+- In `go.opentelemetry.op/otel/exporters/prometheus`, the exporter no longer `Collect`s metrics after `Shutdown` is invoked. (#4648)
+
 ## [1.19.0/0.42.0/0.0.7] 2023-09-28
 
 This release contains the first stable release of the OpenTelemetry Go [metric SDK].

exporters/prometheus/exporter.go

@@ -148,8 +148,11 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	metrics := metricdata.ResourceMetrics{}
 	err := c.reader.Collect(context.TODO(), &metrics)
 	if err != nil {
+		if errors.Is(err, metric.ErrReaderShutdown) {
+			return
+		}
 		otel.Handle(err)
-		if err == metric.ErrReaderNotRegistered {
+		if errors.Is(err, metric.ErrReaderNotRegistered) {
 			return
 		}
 	}

exporters/prometheus/exporter_test.go

@@ -16,6 +16,7 @@ package prometheus
 
 import (
 	"context"
+	"errors"
 	"io"
 	"os"
 	"sync"
@@ -835,3 +836,36 @@ func TestIncompatibleMeterName(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, 1, len(errs))
 }
+
+func TestShutdownExporter(t *testing.T) {
+	var handledError error
+	eh := otel.ErrorHandlerFunc(func(e error) { handledError = errors.Join(handledError, e) })
+	otel.SetErrorHandler(eh)
+
+	ctx := context.Background()
+	registry := prometheus.NewRegistry()
+
+	for i := 0; i < 3; i++ {
+		exporter, err := New(WithRegisterer(registry))
+		require.NoError(t, err)
+		provider := metric.NewMeterProvider(
+			metric.WithResource(resource.Default()),
+			metric.WithReader(exporter))
+		meter := provider.Meter("testmeter")
+		cnt, err := meter.Int64Counter("foo")
+		require.NoError(t, err)
+		cnt.Add(ctx, 100)
+
+		// verify that metrics added to a previously shutdown MeterProvider
+		// do not conflict with metrics added in this loop.
+		_, err = registry.Gather()
+		require.NoError(t, err)
+
+		// Shutdown should cause future prometheus Gather() calls to no longer
+		// include metrics from this loop's MeterProvider.
+		err = provider.Shutdown(ctx)
+		require.NoError(t, err)
+	}
+	// ensure we aren't unnecessarily logging errors from the shutdown MeterProvider
+	require.NoError(t, handledError)
+}