Rephrase async streaming methods

To ensure that the CallOpBuffers stay alive until completion.

include/grpc++/call.h

@@ -57,6 +57,8 @@ class CallOpBuffer final : public CompletionQueueTag {
  public:
   CallOpBuffer() : return_tag_(this) {}
 
+  void Reset(void *next_return_tag);
+
   void AddSendInitialMetadata(std::vector<std::pair<grpc::string, grpc::string> > *metadata);
   void AddSendMessage(const google::protobuf::Message &message);
   void AddRecvMessage(google::protobuf::Message *message);

include/grpc++/stream.h

@@ -330,27 +330,30 @@ class ClientAsyncReader final : public ClientAsyncStreamingInterface,
                ClientContext *context,
                const google::protobuf::Message &request, void* tag)
       : call_(channel->CreateCall(method, context, &cq_)) {
-    CallOpBuffer buf;
-    buf.AddSendMessage(request);
-    buf.AddClientSendClose();
-    call_.PerformOps(&buf);
+    init_buf_.Reset(tag);
+    init_buf_.AddSendMessage(request);
+    init_buf_.AddClientSendClose();
+    call_.PerformOps(&init_buf_);
   }
 
   virtual void Read(R *msg, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddRecvMessage(msg);
-    call_.PerformOps(&buf);
+    read_buf_.Reset(tag);
+    read_buf_.AddRecvMessage(msg);
+    call_.PerformOps(&read_buf_);
   }
 
   virtual void Finish(Status* status, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddClientRecvStatus(status);
-    call_.PerformOps(&buf);
+    finish_buf_.Reset(tag);
+    finish_buf_.AddClientRecvStatus(status);
+    call_.PerformOps(&finish_buf_);
   }
 
  private:
   CompletionQueue cq_;
   Call call_;
+  CallOpBuffer init_buf_;
+  CallOpBuffer read_buf_;
+  CallOpBuffer finish_buf_;
 };
 
 template <class W>
@@ -365,28 +368,31 @@ class ClientAsyncWriter final : public ClientAsyncStreamingInterface,
         call_(channel->CreateCall(method, context, &cq_)) {}
 
   virtual void Write(const W& msg, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddSendMessage(msg);
-    call_.PerformOps(&buf);
+    write_buf_.Reset(tag);
+    write_buf_.AddSendMessage(msg);
+    call_.PerformOps(&write_buf_);
   }
 
-  virtual void WritesDone(void* tag) {
-    CallOpBuffer buf;
-    buf.AddClientSendClose();
-    call_.PerformOps(&buf);
+  virtual void WritesDone(void* tag) override {
+    writes_done_buf_.Reset(tag);
+    writes_done_buf_.AddClientSendClose();
+    call_.PerformOps(&writes_done_buf_);
   }
 
   virtual void Finish(Status* status, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddRecvMessage(response_);
-    buf.AddClientRecvStatus(status);
-    call_.PerformOps(&buf);
+    finish_buf_.Reset(tag);
+    finish_buf_.AddRecvMessage(response_);
+    finish_buf_.AddClientRecvStatus(status);
+    call_.PerformOps(&finish_buf_);
   }
 
  private:
   google::protobuf::Message *const response_;
   CompletionQueue cq_;
   Call call_;
+  CallOpBuffer write_buf_;
+  CallOpBuffer writes_done_buf_;
+  CallOpBuffer finish_buf_;
 };
 
 // Client-side interface for bi-directional streaming.
@@ -400,32 +406,36 @@ class ClientAsyncReaderWriter final : public ClientAsyncStreamingInterface,
       : call_(channel->CreateCall(method, context, &cq_)) {}
 
   virtual void Read(R *msg, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddRecvMessage(msg);
-    call_.PerformOps(&buf);
+    read_buf_.Reset(tag);
+    read_buf_.AddRecvMessage(msg);
+    call_.PerformOps(&read_buf_);
   }
 
   virtual void Write(const W& msg, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddSendMessage(msg);
-    call_.PerformOps(&buf);
+    write_buf_.Reset(tag);
+    write_buf_.AddSendMessage(msg);
+    call_.PerformOps(&write_buf_);
   }
 
-  virtual void WritesDone(void* tag) {
-    CallOpBuffer buf;
-    buf.AddClientSendClose();
-    call_.PerformOps(&buf);
+  virtual void WritesDone(void* tag) override {
+    writes_done_buf_.Reset(tag);
+    writes_done_buf_.AddClientSendClose();
+    call_.PerformOps(&writes_done_buf_);
   }
 
   virtual void Finish(Status* status, void* tag) override {
-    CallOpBuffer buf;
-    buf.AddClientRecvStatus(status);
-    call_.PerformOps(&buf);
+    finish_buf_.Reset(tag);
+    finish_buf_.AddClientRecvStatus(status);
+    call_.PerformOps(&finish_buf_);
   }
 
  private:
   CompletionQueue cq_;
   Call call_;
+  CallOpBuffer read_buf_;
+  CallOpBuffer write_buf_;
+  CallOpBuffer writes_done_buf_;
+  CallOpBuffer finish_buf_;
 };
 
 // TODO(yangg) Move out of stream.h