VM: Fix memory leak during shutdown

runtime/bin/socket.h

 // 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.
 
 #ifndef RUNTIME_BIN_SOCKET_H_
 #define RUNTIME_BIN_SOCKET_H_
 
 #if defined(DART_IO_DISABLED)
 #error "socket.h can only be included on builds with IO enabled"
 #endif
@@ skipping 449 matching lines @@
   static void* GetHashmapKeyFromIntptr(intptr_t i) {
     return reinterpret_cast<void*>(i + 1);
   }
 
   OSSocket* LookupByPort(intptr_t port);
   void InsertByPort(intptr_t port, OSSocket* socket);
   void RemoveByPort(intptr_t port);
 
   OSSocket* LookupByFd(intptr_t fd);
   void InsertByFd(intptr_t fd, OSSocket* socket);
-  void RemoveByFd(intptr_t fd);
 
-  bool CloseOneSafe(OSSocket* os_socket);
+  // If `map_cursor` is provided it will be updated to point to the next
+  // element (in iteration order of `sockets_by_fd`) after `fd` was removed.
+  void RemoveByFd(intptr_t fd, HashMap::Entry** map_cursor);
+
+  bool CloseOneSafe(OSSocket* os_socket, HashMap::Entry** fd_map_cursor);
   void CloseAllSafe();
 
   HashMap sockets_by_port_;
   HashMap sockets_by_fd_;
 
   Mutex* mutex_;
 
   DISALLOW_COPY_AND_ASSIGN(ListeningSocketRegistry);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // RUNTIME_BIN_SOCKET_H_