Avoid doing concurrent DNS resolves of the same hostname

chrome/browser/net/dns_master.cc

 // 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.
 
 #include "chrome/browser/net/dns_master.h"
 
 #include <algorithm>
 #include <set>
 #include <sstream>
 
 #include "base/compiler_specific.h"
 #include "base/histogram.h"
 #include "base/message_loop.h"
 #include "base/lock.h"
 #include "base/stats_counters.h"
 #include "base/string_util.h"
 #include "base/time.h"
 #include "net/base/address_list.h"
 #include "net/base/completion_callback.h"
 #include "net/base/host_resolver.h"
 #include "net/base/net_errors.h"
 
 namespace chrome_browser_net {
 
 class DnsMaster::LookupRequest {
  public:
   LookupRequest(DnsMaster* master,
-                net::HostResolver* /*host_resolver*/,
+                net::HostResolver* host_resolver,
                 const std::string& hostname)
       : ALLOW_THIS_IN_INITIALIZER_LIST(
           net_callback_(this, &LookupRequest::OnLookupFinished)),
         master_(master),
-        hostname_(hostname) {
+        hostname_(hostname),
+        resolver_(host_resolver) {
   }
 
   bool Start() {
     const int result = resolver_.Resolve(hostname_, 80, &addresses_,
                                          &net_callback_);
     return (result == net::ERR_IO_PENDING);
   }
 
  private:
   void OnLookupFinished(int result) {
     master_->OnLookupFinished(this, hostname_, result == net::OK);
   }
 
   // HostResolver will call us using this callback when resolution is complete.
   net::CompletionCallbackImpl<LookupRequest> net_callback_;
 
   DnsMaster* master_;  // Master which started us.
 
   const std::string hostname_;  // Hostname to resolve.
-  net::HostResolver resolver_;
+  net::SingleRequestHostResolver resolver_;
   net::AddressList addresses_;
 
   DISALLOW_COPY_AND_ASSIGN(LookupRequest);
 };
 
 DnsMaster::DnsMaster(net::HostResolver* host_resolver,
                      MessageLoop* host_resolver_loop,
                      size_t max_concurrent)
   : peak_pending_lookups_(0),
     shutdown_(false),
@@ skipping 526 matching lines @@
     std::string hostname(rush_queue_.front());
     rush_queue_.pop();
     return hostname;
   }
   std::string hostname(background_queue_.front());
   background_queue_.pop();
   return hostname;
 }
 
 }  // namespace chrome_browser_net