grpc/examples/cpp/helloworld/greeter_async_client.cc

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#include <iostream>
#include <memory>
#include <string>

#include <grpc++/grpc++.h>
#include <thread>

#include "helloworld.grpc.pb.h"

using grpc::Channel;
using grpc::ClientAsyncResponseReader;
using grpc::ClientContext;
using grpc::CompletionQueue;
using grpc::Status;
using helloworld::HelloRequest;
using helloworld::HelloReply;
using helloworld::Greeter;

class GreeterClient {
 public:
  explicit GreeterClient(std::shared_ptr<Channel> channel)
      : stub_(Greeter::NewStub(channel)) {}

  // Assambles the client's payload, sends it and presents the response back
  // from the server.
  void SayHello(const std::string& user) {
    // Data we are sending to the server.
    HelloRequest request;
    request.set_name(user);

    AsyncClientCall* call = new AsyncClientCall;

    // stub_->AsyncSayHello() perform the RPC call, returning an instance we
    // store in "rpc". Because we are using the asynchronous API, we need the
    // hold on to the "rpc" instance in order to get updates on the ongoing RPC.
    call->response_reader = stub_->AsyncSayHello(&call->context, request, &cq_);


    // Request that, upon completion of the RPC, "reply" be updated with the
    // server's response; "status" with the indication of whether the operation
    // was successful. Tag the request with the memory address of call object.
    call->response_reader->Finish(&call->reply, &call->status, (void*)call);

  }
  void AsyncCompleteRpc()
  {
    void* got_tag;
    bool ok = false;

    // Block until the next result is available in the completion queue "cq".
    while (cq_.Next(&got_tag, &ok))
    {
      AsyncClientCall* call = static_cast<AsyncClientCall*>(got_tag);
      if (ok)
        std::cout << "Greeter received: " << call->reply.message() << std::endl;
      else
        std::cout << "RPC failed" << std::endl;
      delete call;
    }
  }

 private:

  // Structure for keeping state and data information
  struct AsyncClientCall
  {
      // Container for the data we expect from the server.
      HelloReply reply;

      // Context for the client. It could be used to convey extra information to
      // the server and/or tweak certain RPC behaviors.
      ClientContext context;

      // Storage for the status of the RPC upon completion.
      Status status;


      std::unique_ptr<ClientAsyncResponseReader<HelloReply>> response_reader;
  };

  // Out of the passed in Channel comes the stub, stored here, our view of the
  // server's exposed services.
  std::unique_ptr<Greeter::Stub> stub_;

  // The producer-consumer queue we use to communicate asynchronously with the
  // gRPC runtime.
  CompletionQueue cq_;
};

int main(int argc, char** argv) {


  // Instantiate the client. It requires a channel, out of which the actual RPCs
  // are created. This channel models a connection to an endpoint (in this case,
  // localhost at port 50051). We indicate that the channel isn't authenticated
  // (use of InsecureChannelCredentials()).
  GreeterClient greeter(grpc::CreateChannel(
      "localhost:50051", grpc::InsecureChannelCredentials()));

  // Spawn reader thread that loops indefinitely
  std::thread thread_ = std::thread(&GreeterClient::AsyncCompleteRpc, &greeter);

  for (int i = 0; i < 100; i++)
  {
    std::string user("world " + std::to_string(i));
    greeter.SayHello(user);  // The actual RPC call!
  }

  std::cout << "Press control-c to quit" << std::endl << std::endl;
  thread_.join();  //blocks forever

  return 0;
}