Avoid doing concurrent DNS resolves of the same hostname

net/base/client_socket_pool.h

 // Copyright (c) 2006-2008 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_BASE_CLIENT_SOCKET_POOL_H_
 #define NET_BASE_CLIENT_SOCKET_POOL_H_
 
 #include <deque>
 #include <map>
 #include <string>
 
 #include "base/ref_counted.h"
 #include "net/base/completion_callback.h"
 #include "net/base/load_states.h"
 
 namespace net {
 
 class ClientSocket;
 class ClientSocketHandle;
+class HostResolver;
 
 // A ClientSocketPool is used to restrict the number of sockets open at a time.
 // It also maintains a list of idle persistent sockets.
 //
 class ClientSocketPool : public base::RefCounted<ClientSocketPool> {
  public:
   // Requests a connected socket for a group_name.
   //
   // There are four possible results from calling this function:
   // 1) RequestSocket returns OK and initializes |handle| with a reused socket.
@@ skipping 32 matching lines @@
   // Called to release a socket once the socket is no longer needed.  If the
   // socket still has an established connection, then it will be added to the
   // set of idle sockets to be used to satisfy future RequestSocket calls.
   // Otherwise, the ClientSocket is destroyed.
   virtual void ReleaseSocket(const std::string& group_name,
                              ClientSocket* socket) = 0;
 
   // Called to close any idle connections held by the connection manager.
   virtual void CloseIdleSockets() = 0;
 
+  // Returns the HostResolver that will be used for host lookups.
+  virtual HostResolver* GetHostResolver() const = 0;
+
   // The total number of idle sockets in the pool.
   virtual int idle_socket_count() const = 0;
 
   // The total number of idle sockets in a connection group.
   virtual int IdleSocketCountInGroup(const std::string& group_name) const = 0;
 
   // Determine the LoadState of a connecting ClientSocketHandle.
   virtual LoadState GetLoadState(const std::string& group_name,
                                  const ClientSocketHandle* handle) const = 0;
 
  protected:
   ClientSocketPool() {}
   virtual ~ClientSocketPool() {}
 
  private:
   friend class base::RefCounted<ClientSocketPool>;
 
   DISALLOW_COPY_AND_ASSIGN(ClientSocketPool);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_CLIENT_SOCKET_POOL_H_