From 29787dac73147804d6a665b16846dcfbd05bed69 Mon Sep 17 00:00:00 2001
From: David Ashpole <dashpole@google.com>
Date: Fri, 20 Oct 2023 20:09:52 +0000
Subject: [PATCH 1/2] prometheus exporter no longer collects metrics after
 shutdown

---
 CHANGELOG.md                          |  4 ++++
 exporters/prometheus/exporter.go      |  3 +++
 exporters/prometheus/exporter_test.go | 34 +++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2bb7a96733e..903a2288e5a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -39,6 +39,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   Implementors need to update their implementations based on what they want the default behavior of the interface to be.
   See the "API Implementations" section of the `go.opentelemetry.io/otel/trace` package documentation for more informatoin about how to accomplish this. (#4620)
 
+### 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].
diff --git a/exporters/prometheus/exporter.go b/exporters/prometheus/exporter.go
index 8973b2028e6..b525b3e14c1 100644
--- a/exporters/prometheus/exporter.go
+++ b/exporters/prometheus/exporter.go
@@ -148,6 +148,9 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	metrics := metricdata.ResourceMetrics{}
 	err := c.reader.Collect(context.TODO(), &metrics)
 	if err != nil {
+		if err == metric.ErrReaderShutdown {
+			return
+		}
 		otel.Handle(err)
 		if err == metric.ErrReaderNotRegistered {
 			return
diff --git a/exporters/prometheus/exporter_test.go b/exporters/prometheus/exporter_test.go
index 0f211d8318e..bd31657825e 100644
--- a/exporters/prometheus/exporter_test.go
+++ b/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)
+}

From fd16ce32972197eb1725685396e1654c55f2cf6c Mon Sep 17 00:00:00 2001
From: David Ashpole <dashpole@google.com>
Date: Mon, 23 Oct 2023 13:38:23 +0000
Subject: [PATCH 2/2] use errors.Is

---
 exporters/prometheus/exporter.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/exporters/prometheus/exporter.go b/exporters/prometheus/exporter.go
index b525b3e14c1..92651c38cec 100644
--- a/exporters/prometheus/exporter.go
+++ b/exporters/prometheus/exporter.go
@@ -148,11 +148,11 @@ func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	metrics := metricdata.ResourceMetrics{}
 	err := c.reader.Collect(context.TODO(), &metrics)
 	if err != nil {
-		if err == metric.ErrReaderShutdown {
+		if errors.Is(err, metric.ErrReaderShutdown) {
 			return
 		}
 		otel.Handle(err)
-		if err == metric.ErrReaderNotRegistered {
+		if errors.Is(err, metric.ErrReaderNotRegistered) {
 			return
 		}
 	}