[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

net/dns/dns_config_service_win.cc

 // Copyright (c) 2012 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 "net/dns/dns_config_service_win.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 289 matching lines @@
 // up watches requires IO loop.
 class DnsConfigServiceWin::ConfigReader : public SerialWorker {
  public:
   explicit ConfigReader(DnsConfigServiceWin* service)
       : service_(service),
         success_(false) {}
 
   bool StartWatch() {
     DCHECK(loop()->BelongsToCurrentThread());
 
-    // This is done only once per lifetime so open the keys on this thread.
-    base::ThreadRestrictions::ScopedAllowIO allow_io;
-
     base::Closure callback = base::Bind(&SerialWorker::WorkNow,
                                         base::Unretained(this));
 
     // DNS suffix search list and devolution can be configured via group
     // policy which sets this registry key. If the key is missing, the policy
     // does not apply, and the DNS client uses Tcpip and Dnscache settings.
     // If a policy is installed, DnsConfigService will need to be restarted.
     // BUG=99509
     policy_watcher_.StartWatch(
         L"SOFTWARE\\Policies\\Microsoft\\Windows NT\\DNSClient",
@@ skipping 118 matching lines @@
     : config_reader_(new ConfigReader(this)),
       hosts_watcher_(new WatchingFileReader()) {}
 
 DnsConfigServiceWin::~DnsConfigServiceWin() {
   DCHECK(CalledOnValidThread());
   config_reader_->Cancel();
 }
 
 void DnsConfigServiceWin::Watch() {
   DCHECK(CalledOnValidThread());
+
+  // This is done only once per lifetime so open the keys and file watcher
+  // handles on this thread.
+  // TODO(szym): Should/can this be avoided? http://crbug.com/114223
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
   bool started = config_reader_->StartWatch();
   // TODO(szym): handle possible failure
   DCHECK(started);
 
   TCHAR buffer[MAX_PATH];
   UINT rc = GetSystemDirectory(buffer, MAX_PATH);
   DCHECK(0 < rc && rc < MAX_PATH);
   FilePath hosts_path = FilePath(buffer).
       Append(FILE_PATH_LITERAL("drivers\\etc\\hosts"));
   hosts_watcher_->StartWatch(hosts_path, new DnsHostsReader(hosts_path, this));
 }
 
 // static
-DnsConfigService* DnsConfigService::CreateSystemService() {
-  return new DnsConfigServiceWin();
+scoped_ptr<DnsConfigService> DnsConfigService::CreateSystemService() {
+  return scoped_ptr<DnsConfigService>(new DnsConfigServiceWin());
 }
 
 }  // namespace net