otelgrpc: Fix data race in stats handlers when processing messages received and sent metrics

CHANGELOG.md

@@ -15,6 +15,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - Fix `StreamClientInterceptor` in `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc` to end the spans synchronously. (#4537)
+- Fix data race in stats handlers when processing messages received and sent metrics in `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc`. (#4577)
 
 ## [1.21.0/0.46.0/0.15.0/0.1.0] - 2023-11-10
 

instrumentation/google.golang.org/grpc/otelgrpc/stats_handler.go

@@ -195,8 +195,8 @@ func (c *config) handleRPC(ctx context.Context, rs stats.RPCStats) {
 
 		metricAttrs = append(metricAttrs, rpcStatusAttr)
 		c.rpcDuration.Record(wctx, float64(rs.EndTime.Sub(rs.BeginTime)), metric.WithAttributes(metricAttrs...))
-		c.rpcRequestsPerRPC.Record(wctx, gctx.messagesReceived, metric.WithAttributes(metricAttrs...))
-		c.rpcResponsesPerRPC.Record(wctx, gctx.messagesSent, metric.WithAttributes(metricAttrs...))
+		c.rpcRequestsPerRPC.Record(wctx, atomic.LoadInt64(&gctx.messagesReceived), metric.WithAttributes(metricAttrs...))
+		c.rpcResponsesPerRPC.Record(wctx, atomic.LoadInt64(&gctx.messagesSent), metric.WithAttributes(metricAttrs...))
 
 	default:
 		return

instrumentation/google.golang.org/grpc/otelgrpc/test/grpc_stats_handler_test.go

@@ -16,13 +16,17 @@ package test
 
 import (
 	"context"
+	"io"
 	"net"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/interop"
+	"google.golang.org/grpc/status"
 
 	"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
 	"go.opentelemetry.io/otel/attribute"
@@ -31,6 +35,8 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
 
+	testpb "google.golang.org/grpc/interop/grpc_testing"
+
 	"go.opentelemetry.io/otel/sdk/trace"
 	"go.opentelemetry.io/otel/sdk/trace/tracetest"
 	semconv "go.opentelemetry.io/otel/semconv/v1.17.0"
@@ -1316,3 +1322,72 @@ func checkServerMetrics(t *testing.T, reader metric.Reader) {
 
 	metricdatatest.AssertEqual(t, expectedScopeMetric, rm.ScopeMetrics[0], metricdatatest.IgnoreTimestamp(), metricdatatest.IgnoreValue())
 }
+
+// Ensure there is no data race for the following scenario:
+// Bidirectional streaming + client cancels context in the middle of streaming.
+func TestStatsHandlerConcurrentSafeContextCancellation(t *testing.T) {
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	require.NoError(t, err, "failed to open port")
+	client := newGrpcTest(t, listener,
+		[]grpc.DialOption{
+			grpc.WithStatsHandler(otelgrpc.NewClientHandler()),
+		},
+		[]grpc.ServerOption{
+			grpc.StatsHandler(otelgrpc.NewServerHandler()),
+		},
+	)
+
+	const n = 10
+	for i := 0; i < n; i++ {
+		ctx, cancel := context.WithCancel(context.Background())
+		stream, err := client.FullDuplexCall(ctx)
+		require.NoError(t, err)
+
+		const messageCount = 10
+		var wg sync.WaitGroup
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := 0; i < messageCount; i++ {
+				const reqSize = 1
+				pl := interop.ClientNewPayload(testpb.PayloadType_COMPRESSABLE, reqSize)
+				respParam := []*testpb.ResponseParameters{
+					{
+						Size: reqSize,
+					},
+				}
+				req := &testpb.StreamingOutputCallRequest{
+					ResponseType:       testpb.PayloadType_COMPRESSABLE,
+					ResponseParameters: respParam,
+					Payload:            pl,
+				}
+				err := stream.Send(req)
+				if err == io.EOF { // possible due to context cancellation
+					require.ErrorIs(t, ctx.Err(), context.Canceled)
+				} else {
+					require.NoError(t, err)
+				}
+			}
+			require.NoError(t, stream.CloseSend())
+		}()
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for i := 0; i < messageCount; i++ {
+				_, err := stream.Recv()
+				if i > messageCount/2 {
+					cancel()
+				}
+				// must continue to receive messages until server acknowledges the cancellation, to ensure no data race happens there too
+				if status.Code(err) == codes.Canceled {
+					return
+				}
+				require.NoError(t, err)
+			}
+		}()
+
+		wg.Wait()
+	}
+}