Always use NonBlocking IO for UDP sockets on Windows.

net/socket/udp_socket_win.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_SOCKET_UDP_SOCKET_WIN_H_
 #define NET_SOCKET_UDP_SOCKET_WIN_H_
 
 #include <qos2.h>
 #include <stdint.h>
 #include <winsock2.h>
@@ skipping 179 matching lines @@
   // other applications on the same host. See MSDN: http://goo.gl/6vqbj
   int SetMulticastLoopbackMode(bool loopback);
 
   // Sets the differentiated services flags on outgoing packets. May not
   // do anything on some platforms.
   int SetDiffServCodePoint(DiffServCodePoint dscp);
 
   // Resets the thread to be used for thread-safety checks.
   void DetachFromThread();
 
-  // This class by default uses overlapped IO. Call this method before Open()
-  // to switch to non-blocking IO.
-  void UseNonBlockingIO();
-
  private:
   enum SocketOptions {
     SOCKET_OPTION_MULTICAST_LOOP = 1 << 0
   };
 
-  class Core;
-
   void DoReadCallback(int rv);
   void DoWriteCallback(int rv);
 
-  void DidCompleteRead();
-  void DidCompleteWrite();
-
   // base::ObjectWatcher::Delegate implementation.
   void OnObjectSignaled(HANDLE object) override;
   void OnReadSignaled();
   void OnWriteSignaled();
 
   void WatchForReadWrite();
 
   // Handles stats and logging. |result| is the number of bytes transferred, on
   // success, or the net error code on failure.
   void LogRead(int result, const char* bytes, const IPEndPoint* address) const;
@@ skipping 52 matching lines @@
   DatagramSocket::BindType bind_type_;
 
   // PRNG function for generating port numbers.
   RandIntCallback rand_int_cb_;
 
   // These are mutable since they're just cached copies to make
   // GetPeerAddress/GetLocalAddress smarter.
   mutable std::unique_ptr<IPEndPoint> local_address_;
   mutable std::unique_ptr<IPEndPoint> remote_address_;
 
-  // The core of the socket that can live longer than the socket itself. We pass
-  // resources to the Windows async IO functions and we have to make sure that
-  // they are not destroyed while the OS still references them.
-  scoped_refptr<Core> core_;
-
-  // True if non-blocking IO is used.
-  bool use_non_blocking_io_;
-
   // Watches |read_write_event_|.
   base::win::ObjectWatcher read_write_watcher_;
 
   // Events for read and write.
   base::win::ScopedHandle read_write_event_;
 
   // The buffers used in Read() and Write().
   scoped_refptr<IOBuffer> read_iobuffer_;
   scoped_refptr<IOBuffer> write_iobuffer_;
 
@@ skipping 74 matching lines @@
   SetFlowFn set_flow_func_;
 
   FRIEND_TEST_ALL_PREFIXES(UDPSocketTest, SetDSCPFake);
   DISALLOW_COPY_AND_ASSIGN(QwaveAPI);
 };
 
 
 }  // namespace net
 
 #endif  // NET_SOCKET_UDP_SOCKET_WIN_H_