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. Expired()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. SlotReturnFunction(void * data)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 DnsReloadTimer()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 ~DnsReloadTimer()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 DnsReloadTimerHasExpired()93bool 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