net: Move dns_reloader.* into dns directory.

net/base/dns_reloader.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/base/dns_reloader.h"
-
-#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) && \
-    !defined(OS_ANDROID)
-
-#include <resolv.h>
-
-#include "base/basictypes.h"
-#include "base/lazy_instance.h"
-#include "base/logging.h"
-#include "base/message_loop/message_loop.h"
-#include "base/synchronization/lock.h"
-#include "base/threading/thread_local_storage.h"
-#include "net/base/network_change_notifier.h"
-
-namespace net {
-
-namespace {
-
-// On Linux/BSD, changes to /etc/resolv.conf can go unnoticed thus resulting
-// in DNS queries failing either because nameservers are unknown on startup
-// or because nameserver info has changed as a result of e.g. connecting to
-// a new network. Some distributions patch glibc to stat /etc/resolv.conf
-// to try to automatically detect such changes but these patches are not
-// universal and even patched systems such as Jaunty appear to need calls
-// to res_ninit to reload the nameserver information in different threads.
-//
-// To fix this, on systems with FilePathWatcher support, we use
-// NetworkChangeNotifier::DNSObserver to monitor /etc/resolv.conf to
-// enable us to respond to DNS changes and reload the resolver state.
-//
-// OpenBSD does not have thread-safe res_ninit/res_nclose so we can't do
-// the same trick there and most *BSD's don't yet have support for
-// FilePathWatcher (but perhaps the new kqueue mac code just needs to be
-// ported to *BSD to support that).
-//
-// Android does not have /etc/resolv.conf. The system takes care of nameserver
-// changes, so none of this is needed.
-
-class DnsReloader : public NetworkChangeNotifier::DNSObserver {
- public:
-  struct ReloadState {
-    int resolver_generation;
-  };
-
-  // NetworkChangeNotifier::DNSObserver:
-  void OnDNSChanged() override {
-    DCHECK(base::MessageLoopForIO::IsCurrent());
-    base::AutoLock l(lock_);
-    resolver_generation_++;
-  }
-
-  void MaybeReload() {
-    ReloadState* reload_state = static_cast<ReloadState*>(tls_index_.Get());
-    base::AutoLock l(lock_);
-
-    if (!reload_state) {
-      reload_state = new ReloadState();
-      reload_state->resolver_generation = resolver_generation_;
-      res_ninit(&_res);
-      tls_index_.Set(reload_state);
-    } else if (reload_state->resolver_generation != resolver_generation_) {
-      reload_state->resolver_generation = resolver_generation_;
-      // It is safe to call res_nclose here since we know res_ninit will have
-      // been called above.
-      res_nclose(&_res);
-      res_ninit(&_res);
-    }
-  }
-
-  // Free the allocated state.
-  static void SlotReturnFunction(void* data) {
-    ReloadState* reload_state = static_cast<ReloadState*>(data);
-    if (reload_state)
-      res_nclose(&_res);
-    delete reload_state;
-  }
-
- private:
-  DnsReloader() : resolver_generation_(0) {
-    tls_index_.Initialize(SlotReturnFunction);
-    NetworkChangeNotifier::AddDNSObserver(this);
-  }
-
-  ~DnsReloader() override {
-    NOTREACHED();  // LeakyLazyInstance is not destructed.
-  }
-
-  base::Lock lock_;  // Protects resolver_generation_.
-  int resolver_generation_;
-  friend struct base::DefaultLazyInstanceTraits<DnsReloader>;
-
-  // We use thread local storage to identify which ReloadState to interact with.
-  static base::ThreadLocalStorage::StaticSlot tls_index_;
-
-  DISALLOW_COPY_AND_ASSIGN(DnsReloader);
-};
-
-// A TLS slot to the ReloadState for the current thread.
-// static
-base::ThreadLocalStorage::StaticSlot DnsReloader::tls_index_ = TLS_INITIALIZER;
-
-base::LazyInstance<DnsReloader>::Leaky
-    g_dns_reloader = LAZY_INSTANCE_INITIALIZER;
-
-}  // namespace
-
-void EnsureDnsReloaderInit() {
-  g_dns_reloader.Pointer();
-}
-
-void DnsReloaderMaybeReload() {
-  // This routine can be called by any of the DNS worker threads.
-  DnsReloader* dns_reloader = g_dns_reloader.Pointer();
-  dns_reloader->MaybeReload();
-}
-
-}  // namespace net
-
-#endif  // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) &&
-        // !defined(OS_ANDROID)