Avoid doing concurrent DNS resolves of the same hostname

net/tools/fetch/fetch_client.cc

 // Copyright (c) 2009 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 "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/message_loop.h"
 #include "base/singleton.h"
 #include "base/stats_counters.h"
 #include "base/string_util.h"
 #include "net/base/completion_callback.h"
+#include "net/base/host_resolver.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/http/http_cache.h"
 #include "net/http/http_network_layer.h"
 #include "net/http/http_request_info.h"
 #include "net/http/http_transaction.h"
 #include "net/proxy/proxy_service.h"
 
 void usage(const char* program_name) {
   printf("usage: %s --url=<url>  [--n=<clients>] [--stats] [--use_cache]\n",
@@ skipping 96 matching lines @@
     usage(argv[0]);
   int client_limit = 1;
   if (parsed_command_line.HasSwitch(L"n"))
     StringToInt(WideToASCII(parsed_command_line.GetSwitchValue(L"n")),
                 &client_limit);
   bool use_cache = parsed_command_line.HasSwitch(L"use-cache");
 
   // Do work here.
   MessageLoop loop;
 
+  net::HostResolver host_resolver;
   scoped_ptr<net::ProxyService> proxy_service(net::ProxyService::CreateNull());
   net::HttpTransactionFactory* factory = NULL;
   if (use_cache)
-    factory = new net::HttpCache(proxy_service.get(), 0);
+    factory = new net::HttpCache(&host_resolver, proxy_service.get(), 0);
   else
-    factory = new net::HttpNetworkLayer(proxy_service.get());
+    factory = new net::HttpNetworkLayer(&host_resolver, proxy_service.get());
 
   {
     StatsCounterTimer driver_time("FetchClient.total_time");
     StatsScope<StatsCounterTimer> scope(driver_time);
 
     Client** clients = new Client*[client_limit];
     for (int i = 0; i < client_limit; i++)
       clients[i] = new Client(factory, url);
 
     MessageLoop::current()->Run();
@@ skipping 31 matching lines @@
       std::string name(table.GetRowName(index));
       if (name.length() > 0) {
         int value = table.GetRowValue(index);
         printf("%s:\t%d\n", name.c_str(), value);
       }
     }
     printf("</stats>\n");
   }
   return 0;
 }