Don't use same value for socket() and handle(), as they are different concepts.

runtime/bin/eventhandler_win.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/eventhandler.h"
 
 #include <winsock2.h>  // NOLINT
@@ skipping 414 matching lines @@
 
   if (pending_read_ != NULL) {
     CancelIoEx(handle(), pending_read_->GetCleanOverlapped());
     // Don't dispose of the buffer, as it will still complete (with length 0).
   }
 
   DoClose();
 }
 
 
+bool SocketHandle::CreateCompletionPort(HANDLE completion_port) {
+  completion_port_ = CreateIoCompletionPort(reinterpret_cast<HANDLE>(socket()),

[kasperl, 2014/06/04 14:01:05]

Would it make sense to have a non-virtual DoCreateCompletionPort that takes two
handles (the completion port and the socket/handle) so you can share the code?

[Anders Johnsen, 2014/06/04 14:05:22]

Done.

+                                            completion_port,
+                                            reinterpret_cast<ULONG_PTR>(this),
+                                            0);
+  if (completion_port_ == NULL) {
+    return false;
+  }
+  return true;
+}
+
+
 void SocketHandle::HandleIssueError() {
   int error = WSAGetLastError();
   if (error == WSAECONNRESET) {
     HandleClosed(this);
   } else {
     HandleError(this);
   }
   WSASetLastError(error);
 }
 
@@ skipping 918 matching lines @@
 
 
 void EventHandlerImplementation::Shutdown() {
   SendData(kShutdownId, 0, 0);
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)