[examples] Add CPP multiplex example (#33187)

examples/cpp/multiplex/BUILD

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+# 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 = "multiplex_client",
+    srcs = ["multiplex_client.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//examples/protos:helloworld_cc_grpc",
+        "//examples/protos:route_guide",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+    ],
+)
+
+cc_binary(
+    name = "multiplex_server",
+    srcs = ["multiplex_server.cc"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//:grpc++",
+        "//:grpc++_reflection",
+        "//examples/protos:helloworld_cc_grpc",
+        "//examples/protos:route_guide",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/flags:parse",
+        "@com_google_absl//absl/strings:str_format",
+    ],
+)

examples/cpp/multiplex/CMakeLists.txt

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+# 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.
+#
+# cmake build file for C++ helloworld example.
+# Assumes protobuf and gRPC have been installed using cmake.
+# See cmake_externalproject/CMakeLists.txt for all-in-one cmake build
+# that automatically builds all the dependencies before building helloworld.
+
+cmake_minimum_required(VERSION 3.8)
+
+project(Multiplex C CXX)
+
+include(../cmake/common.cmake)
+
+# Proto file
+get_filename_component(hw_proto "../../protos/helloworld.proto" ABSOLUTE)
+get_filename_component(hw_proto_path "${hw_proto}" PATH)
+get_filename_component(rg_proto "../../protos/route_guide.proto" ABSOLUTE)
+get_filename_component(rg_proto_path "${rg_proto}" PATH)
+
+# Generated sources
+set(hw_proto_srcs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.pb.cc")
+set(hw_proto_hdrs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.pb.h")
+set(hw_grpc_srcs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.grpc.pb.cc")
+set(hw_grpc_hdrs "${CMAKE_CURRENT_BINARY_DIR}/helloworld.grpc.pb.h")
+set(rg_proto_srcs "${CMAKE_CURRENT_BINARY_DIR}/route_guide.pb.cc")
+set(rg_proto_hdrs "${CMAKE_CURRENT_BINARY_DIR}/route_guide.pb.h")
+set(rg_grpc_srcs "${CMAKE_CURRENT_BINARY_DIR}/route_guide.grpc.pb.cc")
+set(rg_grpc_hdrs "${CMAKE_CURRENT_BINARY_DIR}/route_guide.grpc.pb.h")
+add_custom_command(
+      OUTPUT "${hw_proto_srcs}" "${hw_proto_hdrs}" "${hw_grpc_srcs}" "${hw_grpc_hdrs}"
+        "${rg_proto_srcs}" "${rg_proto_hdrs}" "${rg_grpc_srcs}" "${rg_grpc_hdrs}"
+      COMMAND ${_PROTOBUF_PROTOC}
+      ARGS --grpc_out "${CMAKE_CURRENT_BINARY_DIR}"
+        --cpp_out "${CMAKE_CURRENT_BINARY_DIR}"
+        -I "${rg_proto_path}"
+        --plugin=protoc-gen-grpc="${_GRPC_CPP_PLUGIN_EXECUTABLE}"
+        "${hw_proto}" "${rg_proto}"
+      DEPENDS "${hw_proto}" "${rg_proto}")
+
+# Include generated *.pb.h files
+include_directories("${CMAKE_CURRENT_BINARY_DIR}")
+
+# example_grpc_proto
+add_library(example_grpc_proto
+  ${hw_grpc_srcs}
+  ${hw_grpc_hdrs}
+  ${hw_proto_srcs}
+  ${hw_proto_hdrs}
+  ${rg_grpc_srcs}
+  ${rg_grpc_hdrs}
+  ${rg_proto_srcs}
+  ${rg_proto_hdrs}
+)
+target_link_libraries(
+  example_grpc_proto
+  ${_REFLECTION}
+  ${_GRPC_GRPCPP}
+  ${_PROTOBUF_LIBPROTOBUF})
+
+# Targets multiplex_(client|server)
+foreach(_target multiplex_client multiplex_server)
+  add_executable(${_target} "${_target}.cc")
+  target_link_libraries(${_target}
+    example_grpc_proto
+    absl::flags
+    absl::flags_parse
+    ${_REFLECTION}
+    ${_GRPC_GRPCPP}
+    ${_PROTOBUF_LIBPROTOBUF})
+endforeach()

examples/cpp/multiplex/README.md

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+# gRPC C++ Multiplexing Example
+
+This example shows how to use a single connection to send multiple concurrent
+asynchronous requests to different services. It also demonstrates multiple
+sharing the same server connection.
+
+[C++ Quick Start]: https://grpc.io/docs/languages/cpp/quickstart

examples/cpp/multiplex/multiplex_client.cc

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+/*
+ *
+ * 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 <grpcpp/grpcpp.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#include "examples/protos/route_guide.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#include "route_guide.grpc.pb.h"
+#endif
+
+ABSL_FLAG(std::string, target, "localhost:50051", "Server address");
+
+using grpc::Channel;
+using grpc::ClientContext;
+using grpc::Status;
+
+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);
+  // We indicate that the channel isn't authenticated (use of
+  // InsecureChannelCredentials()).
+  auto channel =
+      grpc::CreateChannel(target_str, grpc::InsecureChannelCredentials());
+
+  std::mutex mu;
+  std::condition_variable cv;
+  int done_count = 0;
+
+  // Callbacks will be called on background threads
+  std::unique_lock<std::mutex> lock(mu);
+
+  ClientContext hello_context;
+  helloworld::HelloRequest hello_request;
+  helloworld::HelloReply hello_response;
+  Status hello_status;
+
+  ClientContext feature_context;
+  routeguide::Point feature_request;
+  routeguide::Feature feature_response;
+  Status feature_status;
+  // Request to a Greeter service
+  hello_request.set_name("user");
+  helloworld::Greeter::NewStub(channel)->async()->SayHello(
+      &hello_context, &hello_request, &hello_response, [&](Status status) {
+        std::lock_guard<std::mutex> lock(mu);
+        done_count++;
+        hello_status = std::move(status);
+        cv.notify_all();
+      });
+  // Request to a RouteGuide service
+  feature_request.set_latitude(50);
+  feature_request.set_longitude(100);
+  routeguide::RouteGuide::NewStub(channel)->async()->GetFeature(
+      &feature_context, &feature_request, &feature_response,
+      [&](Status status) {
+        std::lock_guard<std::mutex> lock(mu);
+        done_count++;
+        feature_status = std::move(status);
+        cv.notify_all();
+      });
+  // Wait for both requests to finish
+  cv.wait(lock, [&]() { return done_count == 2; });
+  if (hello_status.ok()) {
+    std::cout << "Greeter received: " << hello_response.message() << std::endl;
+  } else {
+    std::cerr << "Greeter failed: " << hello_status.error_message()
+              << std::endl;
+  }
+  if (feature_status.ok()) {
+    std::cout << "Found feature: " << feature_response.name() << std::endl;
+  } else {
+    std::cerr << "Getting feature failed: " << feature_status.error_message()
+              << std::endl;
+  }
+  return 0;
+}

examples/cpp/multiplex/multiplex_server.cc

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+/*
+ *
+ * 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 <map>
+#include <memory>
+#include <string>
+
+#include "absl/flags/flag.h"
+#include "absl/flags/parse.h"
+#include "absl/strings/str_format.h"
+
+#include <grpcpp/ext/proto_server_reflection_plugin.h>
+#include <grpcpp/grpcpp.h>
+#include <grpcpp/health_check_service_interface.h>
+
+#ifdef BAZEL_BUILD
+#include "examples/protos/helloworld.grpc.pb.h"
+#include "examples/protos/route_guide.grpc.pb.h"
+#else
+#include "helloworld.grpc.pb.h"
+#include "route_guide.grpc.pb.h"
+#endif
+
+ABSL_FLAG(uint16_t, port, 50051, "Server port for the service");
+
+using grpc::CallbackServerContext;
+using grpc::Server;
+using grpc::ServerBuilder;
+using grpc::ServerUnaryReactor;
+using grpc::Status;
+using helloworld::Greeter;
+using helloworld::HelloReply;
+using helloworld::HelloRequest;
+using routeguide::RouteGuide;
+
+// Logic and data behind the server's behavior.
+class GreeterServiceImpl final : public Greeter::CallbackService {
+  ServerUnaryReactor* SayHello(CallbackServerContext* context,
+                               const HelloRequest* request,
+                               HelloReply* reply) override {
+    std::string prefix("Hello ");
+    reply->set_message(prefix + request->name());
+
+    ServerUnaryReactor* reactor = context->DefaultReactor();
+    reactor->Finish(Status::OK);
+    return reactor;
+  }
+};
+
+class RouteGuideImpl final : public RouteGuide::CallbackService {
+ public:
+  ServerUnaryReactor* GetFeature(CallbackServerContext* context,
+                                 const routeguide::Point* request,
+                                 routeguide::Feature* response) override {
+    std::string key =
+        absl::StrFormat("%d:%d", request->latitude(), request->longitude());
+    response->set_name(absl::StrFormat("Feature: latitude: %d, longitude: %d",
+                                       request->latitude(),
+                                       request->longitude()));
+    *response->mutable_location() = *request;
+    ServerUnaryReactor* reactor = context->DefaultReactor();
+    reactor->Finish(Status::OK);
+    return reactor;
+  }
+
+ private:
+  std::map<std::string, routeguide::Feature> features_db_;
+};
+
+void RunServer(uint16_t port) {
+  std::string server_address = absl::StrFormat("0.0.0.0:%d", port);
+  GreeterServiceImpl greeter;
+  RouteGuideImpl route_guide;
+
+  grpc::EnableDefaultHealthCheckService(true);
+  grpc::reflection::InitProtoReflectionServerBuilderPlugin();
+  ServerBuilder builder;
+  // Listen on the given address without any authentication mechanism.
+  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
+  // Register "greeter" as the instance through which we'll communicate with
+  // clients. In this case it corresponds to an *synchronous* greeter.
+  builder.RegisterService(&greeter);
+  builder.RegisterService(&route_guide);
+  // 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;
+}