allow null tag

include/grpc++/server_context.h

@@ -128,7 +128,10 @@ class ServerContext {
   // Async only. Has to be called before the rpc starts.
   // Returns the tag in completion queue when the rpc finishes.
   // IsCancelled() can then be called to check whether the rpc was cancelled.
-  void AsyncNotifyWhenDone(void* tag) { async_notify_when_done_tag_ = tag; }
+  void AsyncNotifyWhenDone(void* tag) {
+    has_notify_when_done_tag_ = true;
+    async_notify_when_done_tag_ = tag;
+  }
 
  private:
   friend class ::grpc::testing::InteropContextInspector;
@@ -170,6 +173,7 @@ class ServerContext {
   void set_call(grpc_call* call);
 
   CompletionOp* completion_op_;
+  bool has_notify_when_done_tag_;
   void* async_notify_when_done_tag_;
 
   gpr_timespec deadline_;

src/cpp/server/server_context.cc

@@ -50,18 +50,22 @@ namespace grpc {
 class ServerContext::CompletionOp GRPC_FINAL : public CallOpSetInterface {
  public:
   // initial refs: one in the server context, one in the cq
-  CompletionOp() : refs_(2), finalized_(false), cancelled_(0) {}
+  CompletionOp() : has_tag_(false), tag_(nullptr), refs_(2), finalized_(false), cancelled_(0) {}
 
   void FillOps(grpc_op* ops, size_t* nops) GRPC_OVERRIDE;
   bool FinalizeResult(void** tag, bool* status) GRPC_OVERRIDE;
 
   bool CheckCancelled(CompletionQueue* cq);
 
-  void set_tag(void* tag) { tag_ = tag; }
+  void set_tag(void* tag) {
+    has_tag_ = true;
+    tag_ = tag;
+  }
 
   void Unref();
 
  private:
+  bool has_tag_;
   void* tag_;
   grpc::mutex mu_;
   int refs_;
@@ -94,7 +98,7 @@ bool ServerContext::CompletionOp::FinalizeResult(void** tag, bool* status) {
   grpc::unique_lock<grpc::mutex> lock(mu_);
   finalized_ = true;
   bool ret = false;
-  if (tag_) {
+  if (has_tag_) {
     *tag = tag_;
     ret = true;
   }
@@ -110,6 +114,7 @@ bool ServerContext::CompletionOp::FinalizeResult(void** tag, bool* status) {
 
 ServerContext::ServerContext()
     : completion_op_(nullptr),
+      has_notify_when_done_tag_(false),
       async_notify_when_done_tag_(nullptr),
       call_(nullptr),
       cq_(nullptr),
@@ -118,6 +123,7 @@ ServerContext::ServerContext()
 ServerContext::ServerContext(gpr_timespec deadline, grpc_metadata* metadata,
                              size_t metadata_count)
     : completion_op_(nullptr),
+      has_notify_when_done_tag_(false),
       async_notify_when_done_tag_(nullptr),
       deadline_(deadline),
       call_(nullptr),
@@ -143,7 +149,9 @@ ServerContext::~ServerContext() {
 void ServerContext::BeginCompletionOp(Call* call) {
   GPR_ASSERT(!completion_op_);
   completion_op_ = new CompletionOp();
-  completion_op_->set_tag(async_notify_when_done_tag_);
+  if (has_notify_when_done_tag_) {
+    completion_op_->set_tag(async_notify_when_done_tag_);
+  }
   call->PerformOps(completion_op_);
 }