Modified sample async client to be non-blocking. A reader thread is spawned to handle all the RPC results.

examples/cpp/helloworld/greeter_async_client.cc

@@ -36,6 +36,7 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
+#include <thread>
 
 #include "helloworld.grpc.pb.h"
 
@@ -55,71 +56,91 @@ class GreeterClient {
 
   // Assambles the client's payload, sends it and presents the response back
   // from the server.
-  std::string SayHello(const std::string& user) {
+  void SayHello(const std::string& user) {
     // Data we are sending to the server.
     HelloRequest request;
     request.set_name(user);
 
-    // 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;
-
-    // The producer-consumer queue we use to communicate asynchronously with the
-    // gRPC runtime.
-    CompletionQueue cq;
-
-    // Storage for the status of the RPC upon completion.
-    Status status;
+    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 ongoig RPC.
-    std::unique_ptr<ClientAsyncResponseReader<HelloReply> > rpc(
-        stub_->AsyncSayHello(&context, request, &cq));
+    // 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 integer 1.
-    rpc->Finish(&reply, &status, (void*)1);
+    // 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".
-    cq.Next(&got_tag, &ok);
-
-    // Verify that the result from "cq" corresponds, by its tag, our previous
-    // request.
-    GPR_ASSERT(got_tag == (void*)1);
-    // ... and that the request was completed successfully. Note that "ok"
-    // corresponds solely to the request for updates introduced by Finish().
-    GPR_ASSERT(ok);
-
-    // Act upon the status of the actual RPC.
-    if (status.ok()) {
-      return reply.message();
-    } else {
-      return "RPC failed";
+    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()));
-  std::string user("world");
-  std::string reply = greeter.SayHello(user);  // The actual RPC call!
-  std::cout << "Greeter received: " << reply << std::endl;
+
+  // 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;
 }