net: Move dns_reloader.* into dns directory.
It is DNS specific so it makes more sense to have it in net/dns rather
than in the generic net/base directory.
BUG=None
[email protected]
Review URL: https://codereview.chromium.org/1392943003
Cr-Commit-Position: refs/heads/master@{#352967}
diff --git a/net/dns/dns_reloader.cc b/net/dns/dns_reloader.cc
new file mode 100644
index 0000000..8298c78
--- /dev/null
+++ b/net/dns/dns_reloader.cc
@@ -0,0 +1,125 @@
+// 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_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)
