add a test to confirm producer shutdown is happening as advertised

producer_ext_test.go

@@ -0,0 +1,116 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc_test
+
+import (
+	"context"
+	"strings"
+	"sync/atomic"
+	"testing"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/internal/balancer/stub"
+	"google.golang.org/grpc/internal/stubserver"
+	"google.golang.org/grpc/internal/testutils"
+	testgrpc "google.golang.org/grpc/interop/grpc_testing"
+)
+
+// TestProducerStopsBeforeStateChange confirms that producers are stopped before
+// any state change notification is delivered to the LB policy.
+func (s) TestProducerStopsBeforeStateChange(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+
+	name := strings.ReplaceAll(strings.ToLower(t.Name()), "/", "")
+	var lastProducer *testProducer
+	bf := stub.BalancerFuncs{
+		UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
+			var sc balancer.SubConn
+			sc, err := bd.ClientConn.NewSubConn(ccs.ResolverState.Addresses, balancer.NewSubConnOptions{
+				StateListener: func(scs balancer.SubConnState) {
+					bd.ClientConn.UpdateState(balancer.State{
+						ConnectivityState: scs.ConnectivityState,
+						// We do not pass a picker, but since we don't perform
+						// RPCs, that's okay.
+					})
+					if !lastProducer.stopped.Load() {
+						t.Errorf("lastProducer not stopped before state change notification")
+					}
+					t.Logf("State is now %v; recreating producer", scs.ConnectivityState)
+					p, _ := sc.GetOrBuildProducer(producerBuilderSingleton)
+					lastProducer = p.(*testProducer)
+				},
+			})
+			if err != nil {
+				return err
+			}
+			p, _ := sc.GetOrBuildProducer(producerBuilderSingleton)
+			lastProducer = p.(*testProducer)
+			sc.Connect()
+			return nil
+		},
+	}
+	stub.Register(name, bf)
+
+	ss := stubserver.StubServer{
+		FullDuplexCallF: func(stream testgrpc.TestService_FullDuplexCallServer) error {
+			return nil
+		},
+	}
+	if err := ss.StartServer(); err != nil {
+		t.Fatal("Error starting server:", err)
+	}
+	defer ss.Stop()
+
+	cc, err := grpc.NewClient("dns:///"+ss.Address,
+		grpc.WithDefaultServiceConfig(`{"loadBalancingConfig": [{"`+name+`":{}}]}`),
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	)
+	if err != nil {
+		t.Fatalf("Error creating client: %v", err)
+	}
+	defer cc.Close()
+
+	go cc.Connect()
+	testutils.AwaitState(ctx, t, cc, connectivity.Ready)
+
+	cc.Close()
+	testutils.AwaitState(ctx, t, cc, connectivity.Shutdown)
+}
+
+type producerBuilder struct{}
+
+type testProducer struct {
+	// There should be no race accessing this field, but use an atomic since
+	// the race checker probably can't detect that.
+	stopped atomic.Bool
+}
+
+// Build constructs and returns a producer and its cleanup function
+func (*producerBuilder) Build(cci any) (balancer.Producer, func()) {
+	p := &testProducer{}
+	return p, func() {
+		p.stopped.Store(true)
+	}
+}
+
+var producerBuilderSingleton = &producerBuilder{}