examples/features/gracefulstop: add example to demonstrate server graceful stop

Author: purnesh42H

examples/features/gracefulstop/README.md

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+# Graceful Stop
+
+This example demonstrates how to gracefully stop a gRPC server using Server.GracefulStop().
+
+## How to run
+
+Start the server which will listen to incoming gRPC requests as well as OS
+interrupt signals (SIGINT/SIGTERM). After receiving interrupt signal, it calls
+`s.GracefulStop()` to gracefully shut down the server. If graceful shutdown
+doesn't happen in time, server is stopped forcefully.
+
+```sh
+$ go run server/main.go
+```
+
+In a separate terminal, start the client which will send multiple requests to
+the server with some delay between each request.
+
+```sh
+$ go run client/main.go
+```
+
+Use Ctrl+C or SIGTERM to signal the server to shut down.
+
+The server begins a graceful stop:
+- It finishes ongoing requests.
+- Rejects new incoming requests.
+
+The client will notice the server's shutdown when a request fails.
+

examples/features/gracefulstop/client/main.go

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+/*
+ *
+ * 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.
+ */
+
+// Binary client demonstrates sending multiple requests to server and observe
+// graceful stop.
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials/insecure"
+	pb "google.golang.org/grpc/examples/helloworld/helloworld"
+	"google.golang.org/grpc/status"
+)
+
+var addr = flag.String("addr", "localhost:50052", "the address to connect to")
+
+func main() {
+	flag.Parse()
+
+	// Set up a connection to the server.
+	conn, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		log.Fatalf("Failed to connect: %v", err)
+	}
+	defer conn.Close()
+	c := pb.NewGreeterClient(conn)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	for i := 1; i <= 10; i++ {
+		log.Printf("Calling SayHello %d time", i)
+		r, err := c.SayHello(ctx, &pb.HelloRequest{})
+		if err != nil {
+			if status.Code(err) != codes.InvalidArgument {
+				log.Printf("Received unexpected error: %v", err)
+				continue
+			}
+			log.Printf("Received error: %v", err)
+			continue
+		}
+		log.Printf("Received response: %s", r.Message)
+		time.Sleep(time.Second)
+	}
+
+	log.Printf("Client finished interaction with server.")
+}

examples/features/gracefulstop/server/main.go

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+/*
+ *
+ * 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.
+ */
+
+// Binary server demonstrates how to gracefully stop a gRPC server.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/helloworld/helloworld"
+)
+
+var port = flag.Int("port", 50052, "port number")
+
+// server is used to implement helloworld.GreeterServer.
+type server struct {
+	pb.UnimplementedGreeterServer
+}
+
+// SayHello implements helloworld.GreeterServer.
+func (s *server) SayHello(_ context.Context, _ *pb.HelloRequest) (*pb.HelloReply, error) {
+	return &pb.HelloReply{Message: "Hello"}, nil
+}
+
+func main() {
+	flag.Parse()
+
+	address := fmt.Sprintf(":%v", *port)
+	lis, err := net.Listen("tcp", address)
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+
+	// Create a channel to listen for OS signals.
+	stop := make(chan os.Signal, 1)
+	signal.Notify(stop, os.Interrupt, syscall.SIGTERM)
+
+	s := grpc.NewServer()
+	pb.RegisterGreeterServer(s, &server{})
+
+	go func() {
+		// Wait for an OS signal for graceful shutdown.
+		<-stop
+		fmt.Println("Shutting down server...")
+		s.GracefulStop()
+		close(stop)
+	}()
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	select {
+	case <-stop:
+		log.Printf("Server stopped gracefully")
+	case <-ctx.Done():
+		log.Printf("Graceful stop timeout reached. Forcing server stop.")
+		s.Stop() // Forceful stop
+	}
+}