Reduce frequency of IPv6 probes in HostResolverImpl.

net/dns/host_resolver_impl.cc

Index: net/dns/host_resolver_impl.cc
diff --git a/net/dns/host_resolver_impl.cc b/net/dns/host_resolver_impl.cc
index bd6e43198dca94319fe32227f5bc89475634f90a..a93d460de24dc0e1f6858f30afb2f97396c049b8 100644
--- a/net/dns/host_resolver_impl.cc
+++ b/net/dns/host_resolver_impl.cc
@@ -74,6 +74,10 @@ const unsigned kMinimumTTLSeconds = kCacheEntryTTLSeconds;
 
 const char kLocalhost[] = "localhost.";
 
+// Time between IPv6 probes, i.e. for how long results of each IPv6 probe are
+// cached.
+const int kIpv6ProbePeriodMs = 1000;
+
 // We use a separate histogram name for each platform to facilitate the
 // display of error codes by their symbolic name (since each platform has
 // different mappings).
@@ -1815,6 +1819,7 @@ HostResolverImpl::HostResolverImpl(const Options& options, NetLog* net_log)
       num_dns_failures_(0),
       probe_ipv6_support_(true),
       use_local_ipv6_(false),
+      last_ipv6_probe_result_(false),
       resolved_known_ipv6_hostname_(false),
       additional_resolver_flags_(0),
       fallback_to_proctask_(true),
@@ -2167,7 +2172,7 @@ void HostResolverImpl::SetHaveOnlyLoopbackAddresses(bool result) {
 HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
     const RequestInfo& info,
     const IPAddressNumber* ip_number,
-    const BoundNetLog& net_log) const {
+    const BoundNetLog& net_log) {
   HostResolverFlags effective_flags =
       info.host_resolver_flags() | additional_resolver_flags_;
   AddressFamily effective_address_family = info.address_family();
@@ -2183,19 +2188,13 @@ HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
         // set) so the code requesting the resolution should be amenable to
         // receiving a IPv6 resolution.
         ip_number == nullptr) {
-      // Google DNS address.
-      const uint8 kIPv6Address[] =
-          { 0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00,
-            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88 };
-      IPAddressNumber address(kIPv6Address,
-                              kIPv6Address + arraysize(kIPv6Address));
-      bool rv6 = IsGloballyReachable(address, net_log);
-      net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_IPV6_REACHABILITY_CHECK,
-                       NetLog::BoolCallback("ipv6_available", rv6));
-      if (!rv6) {
+      bool ipv6_available = ProbeIpv6SupportCached(net_log);
+      if (!ipv6_available) {
         effective_address_family = ADDRESS_FAMILY_IPV4;
         effective_flags |= HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
       }
+      net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_IPV6_REACHABILITY_CHECK,
+                       NetLog::BoolCallback("ipv6_available", ipv6_available));

[mmenke, 2015/05/12 14:39:59]

Think this makes more sense in ProbeIpv6SupportCached - maybe also log if the
result was cached or not?

[Sergey Ulanov, 2015/05/12 19:22:24]

Done.

     } else {
       effective_address_family = default_address_family_;
     }
@@ -2210,6 +2209,20 @@ HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
   return Key(hostname, effective_address_family, effective_flags);
 }
 
+bool HostResolverImpl::ProbeIpv6SupportCached(const BoundNetLog& net_log) {

[mmenke, 2015/05/12 14:39:59]

Think this method name is a little weird.  Maybe IsIpv6Reachable?

[Sergey Ulanov, 2015/05/12 19:22:24]

Done. Thanks for suggesting a better name!

+  base::TimeTicks now = base::TimeTicks::Now();
+
+  if ((now - last_ipv6_probe_time_).InMilliseconds() > kIpv6ProbePeriodMs) {
+    // Google DNS address.
+    IPAddressNumber address =
+        { 0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00,
+          0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88 };
+    last_ipv6_probe_result_ = IsGloballyReachable(address, net_log);
+    last_ipv6_probe_time_ = now;
+  }
+  return last_ipv6_probe_result_;
+}
+
 void HostResolverImpl::AbortAllInProgressJobs() {
   // In Abort, a Request callback could spawn new Jobs with matching keys, so
   // first collect and remove all running jobs from |jobs_|.
@@ -2279,6 +2292,7 @@ void HostResolverImpl::TryServingAllJobsFromHosts() {
 
 void HostResolverImpl::OnIPAddressChanged() {
   resolved_known_ipv6_hostname_ = false;
+  last_ipv6_probe_time_ = base::TimeTicks();
   // Abandon all ProbeJobs.
   probe_weak_ptr_factory_.InvalidateWeakPtrs();
   if (cache_.get())