net/dns/host_resolver.cc

   1 // Copyright (c) 2012 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/dns/host_resolver.h"
   6
   7 #include "base/logging.h"
   8 #include "base/metrics/field_trial.h"
   9 #include "base/strings/string_number_conversions.h"
  10 #include "base/strings/string_split.h"
  11 #include "net/dns/dns_client.h"
  12 #include "net/dns/dns_config_service.h"
  13 #include "net/dns/host_cache.h"
  14 #include "net/dns/host_resolver_impl.h"
  15
  16 namespace net {
  17
  18 namespace {
  19
  20 // Maximum of 6 concurrent resolver threads (excluding retries).
  21 // Some routers (or resolvers) appear to start to provide host-not-found if
  22 // too many simultaneous resolutions are pending.  This number needs to be
  23 // further optimized, but 8 is what FF currently does. We found some routers
  24 // that limit this to 6, so we're temporarily holding it at that level.
  25 const size_t kDefaultMaxProcTasks = 6u;
  26
  27 }  // namespace
  28
  29 PrioritizedDispatcher::Limits HostResolver::Options::GetDispatcherLimits()
  30     const {
  31   PrioritizedDispatcher::Limits limits(NUM_PRIORITIES, max_concurrent_resolves);
  32
  33   // If not using default, do not use the field trial.
  34   if (limits.total_jobs != HostResolver::kDefaultParallelism)
  35     return limits;
  36
  37   // Default, without trial is no reserved slots.
  38   limits.total_jobs = kDefaultMaxProcTasks;
  39
  40   // Parallelism is determined by the field trial.
  41   std::string group = base::FieldTrialList::FindFullName(
  42       "HostResolverDispatch");
  43
  44   if (group.empty())
  45     return limits;
  46
  47   // The format of the group name is a list of non-negative integers separated
  48   // by ':'. Each of the elements in the list corresponds to an element in
  49   // |reserved_slots|, except the last one which is the |total_jobs|.
  50
  51   std::vector<std::string> group_parts;
  52   base::SplitString(group, ':', &group_parts);
  53   if (group_parts.size() != NUM_PRIORITIES + 1) {
  54     NOTREACHED();
  55     return limits;
  56   }
  57
  58   std::vector<size_t> parsed(group_parts.size());
  59   size_t total_reserved_slots = 0;
  60
  61   for (size_t i = 0; i < group_parts.size(); ++i) {
  62     if (!base::StringToSizeT(group_parts[i], &parsed[i])) {
  63       NOTREACHED();
  64       return limits;
  65     }
  66   }
  67
  68   size_t total_jobs = parsed.back();
  69   parsed.pop_back();
  70   for (size_t i = 0; i < parsed.size(); ++i) {
  71     total_reserved_slots += parsed[i];
  72   }
  73
  74   // There must be some unreserved slots available for the all priorities.
  75   if (total_reserved_slots > total_jobs ||
  76       (total_reserved_slots == total_jobs && parsed[MINIMUM_PRIORITY] == 0)) {
  77     NOTREACHED();
  78     return limits;
  79   }
  80
  81   limits.total_jobs = total_jobs;
  82   limits.reserved_slots = parsed;
  83   return limits;
  84 }
  85
  86 HostResolver::Options::Options()
  87     : max_concurrent_resolves(kDefaultParallelism),
  88       max_retry_attempts(kDefaultRetryAttempts),
  89       enable_caching(true) {
  90 }
  91
  92 HostResolver::RequestInfo::RequestInfo(const HostPortPair& host_port_pair)
  93     : host_port_pair_(host_port_pair),
  94       address_family_(ADDRESS_FAMILY_UNSPECIFIED),
  95       host_resolver_flags_(0),
  96       allow_cached_response_(true),
  97       is_speculative_(false),
  98       is_my_ip_address_(false) {}
  99
 100 HostResolver::~HostResolver() {
 101 }
 102
 103 void HostResolver::SetDnsClientEnabled(bool enabled) {
 104 }
 105
 106 HostCache* HostResolver::GetHostCache() {
 107   return NULL;
 108 }
 109
 110 base::Value* HostResolver::GetDnsConfigAsValue() const {
 111   return NULL;
 112 }
 113
 114 // static
 115 scoped_ptr<HostResolver> HostResolver::CreateSystemResolver(
 116     const Options& options,
 117     NetLog* net_log) {
 118   return scoped_ptr<HostResolver>(new HostResolverImpl(options, net_log));
 119 }
 120
 121 // static
 122 scoped_ptr<HostResolver> HostResolver::CreateDefaultResolver(NetLog* net_log) {
 123   return scoped_ptr<HostResolver>(new HostResolverImpl(Options(), net_log));
 124 }
 125
 126 HostResolver::HostResolver() {
 127 }
 128
 129 }  // namespace net