Split off the DNS reload timer

net/base/dns_reload_timer.cc

+// Copyright (c) 2010 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_reload_timer.h"
+
+#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+#include "base/singleton.h"
+#include "base/thread_local_storage.h"
+#include "base/time.h"
+
+namespace net {
+
+// 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.
+//
+// We adopt the Mozilla solution here which is to call res_ninit when
+// lookups fail and to rate limit the reloading to once per second per
+// thread.
+//
+// OpenBSD does not have thread-safe res_ninit/res_nclose so we can't do
+// the same trick there.
+
+// Keep a timer per calling thread to rate limit the calling of res_ninit.
+class DnsReloadTimer {
+ public:
+  // Check if the timer for the calling thread has expired. When no
+  // timer exists for the calling thread, create one.
+  bool Expired() {
+    const base::TimeDelta kRetryTime = base::TimeDelta::FromSeconds(1);
+    base::TimeTicks now = base::TimeTicks::Now();
+    base::TimeTicks* timer_ptr =
+      static_cast<base::TimeTicks*>(tls_index_.Get());
+
+    if (!timer_ptr) {
+      timer_ptr = new base::TimeTicks();
+      *timer_ptr = base::TimeTicks::Now();
+      tls_index_.Set(timer_ptr);
+      // Return true to reload dns info on the first call for each thread.
+      return true;
+    } else if (now - *timer_ptr > kRetryTime) {
+      *timer_ptr = now;
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  // Free the allocated timer.
+  static void SlotReturnFunction(void* data) {
+    base::TimeTicks* tls_data = static_cast<base::TimeTicks*>(data);
+    delete tls_data;
+  }
+
+ private:
+  friend struct DefaultSingletonTraits<DnsReloadTimer>;
+
+  DnsReloadTimer() {
+    // During testing the DnsReloadTimer Singleton may be created and destroyed
+    // multiple times. Initialize the ThreadLocalStorage slot only once.
+    if (!tls_index_.initialized())
+      tls_index_.Initialize(SlotReturnFunction);
+  }
+
+  ~DnsReloadTimer() {
+  }
+
+  // We use thread local storage to identify which base::TimeTicks to
+  // interact with.
+  static ThreadLocalStorage::Slot tls_index_ ;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsReloadTimer);
+};
+
+// A TLS slot to the TimeTicks for the current thread.
+// static
+ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(base::LINKER_INITIALIZED);
+
+bool DnsReloadTimerHasExpired() {
+  DnsReloadTimer* dns_timer = Singleton<DnsReloadTimer>::get();
+  return dns_timer->Expired();
+}
+
+}  // namespace net
+
+#endif  // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)