Change AsyncUDP's readCallback to be protected.

Summary: Change AsyncUDPSocket's ReadCallback to be protected so that subclasses can have access to it.

Reviewed By: yangchi

Differential Revision: D5376012

fbshipit-source-id: 7ec21d9bfe6bde525253adea7abf5dea15fb7fa0

folly/io/async/AsyncUDPSocket.cpp

@@ -36,9 +36,9 @@ namespace folly {
 
 AsyncUDPSocket::AsyncUDPSocket(EventBase* evb)
     : EventHandler(CHECK_NOTNULL(evb)),
+      readCallback_(nullptr),
       eventBase_(evb),
-      fd_(-1),
-      readCallback_(nullptr) {
+      fd_(-1) {
   evb->dcheckIsInEventBaseThread();
 }
 

folly/io/async/AsyncUDPSocket.h

@@ -167,6 +167,9 @@ class AsyncUDPSocket : public EventHandler {
     return ::sendmsg(socket, message, flags);
   }
 
+  // Non-null only when we are reading
+  ReadCallback* readCallback_;
+
  private:
   AsyncUDPSocket(const AsyncUDPSocket&) = delete;
   AsyncUDPSocket& operator=(const AsyncUDPSocket&) = delete;
@@ -186,9 +189,6 @@ class AsyncUDPSocket : public EventHandler {
   // Temp space to receive client address
   folly::SocketAddress clientAddress_;
 
-  // Non-null only when we are reading
-  ReadCallback* readCallback_;
-
   bool reuseAddr_{true};
   bool reusePort_{false};
 };