[Example] Added gRPC C++ cancellation example (grpc#34239)

examples/cpp/cancellation/BUILD

@@ -0,0 +1,39 @@
+# Copyright 2023 the 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.
+
+licenses(["notice"])
+
+cc_binary(
+    name = "client",
+    srcs = ["client.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+    ],
+)
+
+cc_binary(
+    name = "server",
+    srcs = ["server.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//examples/protos:helloworld_cc_grpc",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+    ],
+)

examples/cpp/cancellation/README.md

@@ -0,0 +1,37 @@
+# Cancellation Example
+
+## Overview
+
+This example shows you how to cancel from the client and how to get informed on the server and the client.
+
+### Try it!
+
+Once you have working gRPC, you can build this example using either bazel or cmake.
+
+Run the server, which will listen on port 50051:
+
+```sh
+$ ./server
+```
+
+Run the client (in a different terminal):
+
+```sh
+$ ./client
+```
+
+If things go smoothly, you will see the client output:
+
+```
+Begin : Begin Ack
+Count 1 : Count 1 Ack
+Count 2 : Count 2 Ack
+Count 3 : Count 3 Ack
+Count 4 : Count 4 Ack
+Count 5 : Count 5 Ack
+Count 6 : Count 6 Ack
+Count 7 : Count 7 Ack
+Count 8 : Count 8 Ack
+Count 9 : Count 9 Ack
+RPC Cancelled!
+```

examples/cpp/cancellation/client.cc

@@ -0,0 +1,119 @@
+// Copyright 2023 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.
+
+#include <condition_variable>
+#include <iostream>
+#include <memory>
+#include <mutex>
+#include <string>
+#include <vector>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/strings/str_cat.h"
+
+#include <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(std::string, target, "localhost:50051", "Server address");
+
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Status;
+using grpc::StatusCode;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+// Requests each key in the vector and displays the key and its corresponding
+// value as a pair.
+class KeyValueStoreClient
+    : public grpc::ClientBidiReactor<HelloRequest, HelloReply> {
+ public:
+  KeyValueStoreClient(std::shared_ptr<Channel> channel)
+      : stub_(Greeter::NewStub(channel)) {
+    stub_->async()->SayHelloBidiStream(&context_, this);
+    request_.set_name("Begin");
+    StartWrite(&request_);
+    StartCall();
+  }
+
+  void OnReadDone(bool ok) override {
+    if (ok) {
+      std::cout << request_.name() << " : " << response_.message() << std::endl;
+      if (++counter_ < 10) {
+        request_.set_name(absl::StrCat("Count ", counter_));
+        StartWrite(&request_);
+      } else {
+        // Cancel after sending 10 messages
+        context_.TryCancel();
+      }
+    }
+  }
+
+  void OnWriteDone(bool ok) override {
+    if (ok) {
+      StartRead(&response_);
+    }
+  }
+
+  void OnDone(const grpc::Status& status) override {
+    if (!status.ok()) {
+      if (status.error_code() == StatusCode::CANCELLED) {
+        // Eventually client will know here that call is cancelled.
+        std::cout << "RPC Cancelled!" << std::endl;
+      } else {
+        std::cout << "RPC Failed: " << status.error_code() << ": "
+                  << status.error_message() << std::endl;
+      }
+    }
+    std::unique_lock<std::mutex> l(mu_);
+    done_ = true;
+    cv_.notify_all();
+  }
+
+  void Await() {
+    std::unique_lock<std::mutex> l(mu_);
+    while (!done_) {
+      cv_.wait(l);
+    }
+  }
+
+ private:
+  std::unique_ptr<Greeter::Stub> stub_;
+  size_t counter_ = 0;
+  ClientContext context_;
+  bool done_ = false;
+  HelloRequest request_;
+  HelloReply response_;
+  std::mutex mu_;
+  std::condition_variable cv_;
+};
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  // Instantiate the client. It requires a channel, out of which the actual RPCs
+  // are created. This channel models a connection to an endpoint specified by
+  // the argument "--target=" which is the only expected argument.
+  std::string target_str = absl::GetFlag(FLAGS_target);
+  KeyValueStoreClient client(
+      grpc::CreateChannel(target_str, grpc::InsecureChannelCredentials()));
+  client.Await();
+  return 0;
+}

examples/cpp/cancellation/server.cc

@@ -0,0 +1,104 @@
+// Copyright 2023 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.
+
+#include <iostream>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/strings/str_format.h"
+
+#include <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#endif
+
+ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");
+
+using grpc::CallbackServerContext;
+using grpc::Server;
+using grpc::ServerBidiReactor;
+using grpc::ServerBuilder;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+
+// Logic behind the server's behavior.
+class KeyValueStoreServiceImpl final : public Greeter::CallbackService {
+  ServerBidiReactor<HelloRequest, HelloReply>* SayHelloBidiStream(
+      CallbackServerContext* context) override {
+    class Reactor : public ServerBidiReactor<HelloRequest, HelloReply> {
+     public:
+      explicit Reactor() { StartRead(&request_); }
+
+      void OnReadDone(bool ok) override {
+        if (!ok) {
+          // Client cancelled it
+          std::cout << "OnReadDone Cancelled!" << std::endl;
+          return Finish(grpc::Status::CANCELLED);
+        }
+        response_.set_message(absl::StrCat(request_.name(), " Ack"));
+        StartWrite(&response_);
+      }
+
+      void OnWriteDone(bool ok) override {
+        if (!ok) {
+          // Client cancelled it
+          std::cout << "OnWriteDone Cancelled!" << std::endl;
+          return Finish(grpc::Status::CANCELLED);
+        }
+        StartRead(&request_);
+      }
+
+      void OnDone() override { delete this; }
+
+     private:
+      HelloRequest request_;
+      HelloReply response_;
+    };
+
+    return new Reactor();
+  }
+};
+
+void RunServer(uint16_t port) {
+  std::string server_address = absl::StrFormat("0.0.0.0:%d", port);
+  KeyValueStoreServiceImpl service;
+
+  ServerBuilder builder;
+  // Listen on the given address without any authentication mechanism.
+  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
+  // Register "service" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* service.
+  builder.RegisterService(&service);
+  // Finally assemble the server.
+  std::unique_ptr<Server> server(builder.BuildAndStart());
+  std::cout << "Server listening on " << server_address << std::endl;
+
+  // Wait for the server to shutdown. Note that some other thread must be
+  // responsible for shutting down the server for this call to ever return.
+  server->Wait();
+}
+
+int main(int argc, char** argv) {
+  absl::ParseCommandLine(argc, argv);
+  RunServer(absl::GetFlag(FLAGS_port));
+  return 0;
+}

examples/protos/helloworld.proto

@@ -27,6 +27,8 @@ service Greeter {
   rpc SayHello (HelloRequest) returns (HelloReply) {}
 
   rpc SayHelloStreamReply (HelloRequest) returns (stream HelloReply) {}
+
+  rpc SayHelloBidiStream (stream HelloRequest) returns (stream HelloReply) {}
 }
 
 // The request message containing the user's name.