From 470cbd1c6e0f1e4d49265a1ed403ffb1219fffa6 Mon Sep 17 00:00:00 2001
From: Michael Yeh <miyeh@cisco.com>
Date: Wed, 4 May 2016 12:39:20 -0700
Subject: Created a new sample async client that is non-blocking.  A reader
 thread is spawned to handle all the RPC results.

---
 examples/cpp/helloworld/greeter_async_client.cc | 93 ++++++++++---------------
 1 file changed, 36 insertions(+), 57 deletions(-)

(limited to 'examples/cpp/helloworld/greeter_async_client.cc')

diff --git a/examples/cpp/helloworld/greeter_async_client.cc b/examples/cpp/helloworld/greeter_async_client.cc
index ca5a7defb0..35014267fe 100644
--- a/examples/cpp/helloworld/greeter_async_client.cc
+++ b/examples/cpp/helloworld/greeter_async_client.cc
@@ -36,7 +36,6 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
-#include <thread>
 
 #include "helloworld.grpc.pb.h"
 
@@ -56,91 +55,71 @@ class GreeterClient {
 
   // Assambles the client's payload, sends it and presents the response back
   // from the server.
-  void SayHello(const std::string& user) {
+  std::string SayHello(const std::string& user) {
     // Data we are sending to the server.
     HelloRequest request;
     request.set_name(user);
 
-    AsyncClientCall* call = new 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;
+
+    // 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;
 
     // 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_);
-
+    // 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));
 
     // 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()
-  {
+    // was successful. Tag the request with the integer 1.
+    rpc->Finish(&reply, &status, (void*)1);
     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;
+    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";
     }
   }
 
  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
+  std::string user("world");
+  std::string reply = greeter.SayHello(user);  // The actual RPC call!
+  std::cout << "Greeter received: " << reply << std::endl;
 
   return 0;
 }
-- 
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