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      1 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "net/base/dns_reload_timer.h"
      6 
      7 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
      8 #include "base/lazy_instance.h"
      9 #include "base/threading/thread_local_storage.h"
     10 #include "base/time.h"
     11 
     12 namespace {
     13 
     14 // On Linux/BSD, changes to /etc/resolv.conf can go unnoticed thus resulting
     15 // in DNS queries failing either because nameservers are unknown on startup
     16 // or because nameserver info has changed as a result of e.g. connecting to
     17 // a new network. Some distributions patch glibc to stat /etc/resolv.conf
     18 // to try to automatically detect such changes but these patches are not
     19 // universal and even patched systems such as Jaunty appear to need calls
     20 // to res_ninit to reload the nameserver information in different threads.
     21 //
     22 // We adopt the Mozilla solution here which is to call res_ninit when
     23 // lookups fail and to rate limit the reloading to once per second per
     24 // thread.
     25 //
     26 // OpenBSD does not have thread-safe res_ninit/res_nclose so we can't do
     27 // the same trick there.
     28 
     29 // Keep a timer per calling thread to rate limit the calling of res_ninit.
     30 class DnsReloadTimer {
     31  public:
     32   // Check if the timer for the calling thread has expired. When no
     33   // timer exists for the calling thread, create one.
     34   bool Expired() {
     35     const base::TimeDelta kRetryTime = base::TimeDelta::FromSeconds(1);
     36     base::TimeTicks now = base::TimeTicks::Now();
     37     base::TimeTicks* timer_ptr =
     38       static_cast<base::TimeTicks*>(tls_index_.Get());
     39 
     40     if (!timer_ptr) {
     41       timer_ptr = new base::TimeTicks();
     42       *timer_ptr = base::TimeTicks::Now();
     43       tls_index_.Set(timer_ptr);
     44       // Return true to reload dns info on the first call for each thread.
     45       return true;
     46     } else if (now - *timer_ptr > kRetryTime) {
     47       *timer_ptr = now;
     48       return true;
     49     } else {
     50       return false;
     51     }
     52   }
     53 
     54   // Free the allocated timer.
     55   static void SlotReturnFunction(void* data) {
     56     base::TimeTicks* tls_data = static_cast<base::TimeTicks*>(data);
     57     delete tls_data;
     58   }
     59 
     60  private:
     61   friend struct base::DefaultLazyInstanceTraits<DnsReloadTimer>;
     62 
     63   DnsReloadTimer() {
     64     // During testing the DnsReloadTimer Singleton may be created and destroyed
     65     // multiple times. Initialize the ThreadLocalStorage slot only once.
     66     if (!tls_index_.initialized())
     67       tls_index_.Initialize(SlotReturnFunction);
     68   }
     69 
     70   ~DnsReloadTimer() {
     71   }
     72 
     73   // We use thread local storage to identify which base::TimeTicks to
     74   // interact with.
     75   static base::ThreadLocalStorage::Slot tls_index_ ;
     76 
     77   DISALLOW_COPY_AND_ASSIGN(DnsReloadTimer);
     78 };
     79 
     80 // A TLS slot to the TimeTicks for the current thread.
     81 // static
     82 base::ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(
     83     base::LINKER_INITIALIZED);
     84 
     85 base::LazyInstance<DnsReloadTimer,
     86                    base::LeakyLazyInstanceTraits<DnsReloadTimer> >
     87     g_dns_reload_timer(base::LINKER_INITIALIZED);
     88 
     89 }  // namespace
     90 
     91 namespace net {
     92 
     93 bool DnsReloadTimerHasExpired() {
     94   DnsReloadTimer* dns_timer = g_dns_reload_timer.Pointer();
     95   return dns_timer->Expired();
     96 }
     97 
     98 }  // namespace net
     99 
    100 #endif  // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
    101