Ensured server call delete happens after all OnDone handlers are called.

stout/grpc/server.cc

@@ -6,6 +6,14 @@ namespace grpc {
 ServerCallBase::ServerCallBase(std::unique_ptr<ServerContext>&& context, CallType type)
   : status_(ServerCallStatus::Ok), context_(std::move(context)), type_(type)
 {
+  // NOTE: we rely on the explicit design of Notification where the
+  // ***first*** handler added via 'Watch()' will be the last handler
+  // that gets executed in order to trigger 'donedonedone_' after
+  // we've triggered all of the other 'OnDone()' handlers.
+  done_.Watch([this](bool cancelled) {
+    donedonedone_.Notify(cancelled);
+  });
+
   // NOTE: 'context_->OnDone()' NOT 'this->OnDone()'.
   context_->OnDone([this](bool cancelled) {
     // NOTE: emperical evidence shows that gRPC may invoke the done

stout/grpc/server.h

@@ -758,6 +758,14 @@ class ServerCallBase : public CallBase
   }
 
 private:
+  friend class Server;
+
+  template <typename F>
+  void OnDoneDoneDone(F&& f)
+  {
+    donedonedone_.Watch(f);
+  }
+
   ServerCallStatus write(
       ::grpc::ByteBuffer* buffer,
       ::grpc::WriteOptions options)
@@ -814,6 +822,7 @@ class ServerCallBase : public CallBase
   std::unique_ptr<ServerContext> context_;
 
   Notification<bool> done_;
+  Notification<bool> donedonedone_;
 
   CallType type_;
 };
@@ -1064,10 +1073,9 @@ std::enable_if_t<
     auto call = borrow(
         new ServerCall<Request, Response>(std::move(context)),
         [](auto* call) {
-          // NOTE: see note in ServerCallBase constructor as to the
-          // invariant that we must set up our 'OnDone' handler
-          // *after* the ServerCallBase constructor.
-          call->OnDone([](auto* call, bool) {
+          // NOTE: using private 'OnDoneDoneDone()' which gets invoked
+          // *after* all of the other 'OnDone()' handlers.
+          call->OnDoneDoneDone([call](bool) {
             delete call;
           });
         });