Avoid doing concurrent DNS resolves of the same hostname

chrome/browser/net/chrome_url_request_context.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/chrome_url_request_context.h"
 
 #include "base/command_line.h"
 #include "base/string_util.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_thread.h"
 #include "chrome/browser/extensions/extensions_service.h"
 #include "chrome/browser/extensions/user_script_master.h"
+#include "chrome/browser/net/dns_global.h"
 #include "chrome/browser/profile.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/notification_service.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "net/ftp/ftp_network_layer.h"
 #include "net/http/http_cache.h"
 #include "net/http/http_network_layer.h"
@@ skipping 79 matching lines @@
       g_browser_process->io_thread()->message_loop());
 }
 
 // static
 ChromeURLRequestContext* ChromeURLRequestContext::CreateOriginal(
     Profile* profile, const FilePath& cookie_store_path,
     const FilePath& disk_cache_path) {
   DCHECK(!profile->IsOffTheRecord());
   ChromeURLRequestContext* context = new ChromeURLRequestContext(profile);
 
+  // Global host resolver for the context.
+  context->host_resolver_ = chrome_browser_net::GetGlobalHostResolver();
+
   context->proxy_service_ = CreateProxyService(
       context, *CommandLine::ForCurrentProcess());
 
   net::HttpCache* cache =
-      new net::HttpCache(context->proxy_service_,
+      new net::HttpCache(context->host_resolver_,
+                         context->proxy_service_,
                          disk_cache_path.ToWStringHack(), 0);
 
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
   bool record_mode = chrome::kRecordModeEnabled &&
                      command_line.HasSwitch(switches::kRecordMode);
   bool playback_mode = command_line.HasSwitch(switches::kPlaybackMode);
 
   if (record_mode || playback_mode) {
     // Don't use existing cookies and use an in-memory store.
     context->cookie_store_ = new net::CookieMonster();
     cache->set_mode(
         record_mode ? net::HttpCache::RECORD : net::HttpCache::PLAYBACK);
   }
   context->http_transaction_factory_ = cache;
 
   // The kNewFtp switch is Windows specific only because we have multiple FTP
   // implementations on Windows.
 #if defined(OS_WIN)
   if (command_line.HasSwitch(switches::kNewFtp))
-    context->ftp_transaction_factory_ = new net::FtpNetworkLayer;
+    context->ftp_transaction_factory_ =
+        new net::FtpNetworkLayer(context->host_resolver_);
 #else
-  context->ftp_transaction_factory_ = new net::FtpNetworkLayer;
+  context->ftp_transaction_factory_ =
+      new net::FtpNetworkLayer(context->host_resolver_);
 #endif
 
   // setup cookie store
   if (!context->cookie_store_) {
     DCHECK(!cookie_store_path.empty());
     context->cookie_db_.reset(new SQLitePersistentCookieStore(
         cookie_store_path.ToWStringHack(),
         g_browser_process->db_thread()->message_loop()));
     context->cookie_store_ = new net::CookieMonster(context->cookie_db_.get());
   }
@@ skipping 27 matching lines @@
 
   return context;
 }
 
 // static
 ChromeURLRequestContext* ChromeURLRequestContext::CreateOffTheRecord(
     Profile* profile) {
   DCHECK(profile->IsOffTheRecord());
   ChromeURLRequestContext* context = new ChromeURLRequestContext(profile);
 
-  // Share the same proxy service as the original profile. This proxy
-  // service's lifespan is dependent on the lifespan of the original profile,
-  // which we reference (see above).
+  // Share the same proxy service and host resolver as the original profile.
+  // This proxy service's lifespan is dependent on the lifespan of the original
+  // profile which we reference (see above).
+  context->host_resolver_ =
+      profile->GetOriginalProfile()->GetRequestContext()->host_resolver();
   context->proxy_service_ =
       profile->GetOriginalProfile()->GetRequestContext()->proxy_service();
 
   context->http_transaction_factory_ =
-      new net::HttpCache(context->proxy_service_, 0);
+      new net::HttpCache(context->host_resolver_, context->proxy_service_, 0);
   context->cookie_store_ = new net::CookieMonster;
 
   return context;
 }
 
 // static
 ChromeURLRequestContext*
 ChromeURLRequestContext::CreateOffTheRecordForExtensions(Profile* profile) {
   DCHECK(profile->IsOffTheRecord());
   ChromeURLRequestContext* context = new ChromeURLRequestContext(profile);
@@ skipping 30 matching lines @@
     // by HttpNetworkLayer so we can reuse HttpNetworkSession within it. This
     // assumption will be invalid if the original HttpCache is constructed with
     // HttpCache(HttpTransactionFactory*, disk_cache::Backend*) constructor.
     net::HttpNetworkLayer* original_network_layer =
         static_cast<net::HttpNetworkLayer*>(original_cache->network_layer());
     cache = new net::HttpCache(original_network_layer->GetSession(),
                                disk_cache_path.ToWStringHack(), 0);
   } else {
     // If original HttpCache doesn't exist, simply construct one with a whole
     // new set of network stack.
-    cache = new net::HttpCache(original_context->proxy_service(),
+    cache = new net::HttpCache(original_context->host_resolver(),
+                               original_context->proxy_service(),
                                disk_cache_path.ToWStringHack(), 0);
   }
 
   cache->set_type(net::MEDIA_CACHE);
   context->http_transaction_factory_ = cache;
   return context;
 }
 
 ChromeURLRequestContext::ChromeURLRequestContext(Profile* profile)
     : prefs_(profile->GetPrefs()),
@@ skipping 155 matching lines @@
 
   // Do not delete the cookie store in the case of the media context, as it is
   // owned by the original context.
   if (!is_media_)
     delete cookie_store_;
 
   // Do not delete the proxy service in the case of OTR or media contexts, as
   // it is owned by the original URLRequestContext.
   if (!is_off_the_record_ && !is_media_)
     delete proxy_service_;
+
+  // Do not delete host_resolver_; it will be freed by FreeGlobalHostResolver()
+  // during the teardown of DNS prefetching.
 }