[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

net/base/host_resolver_impl.cc

Index: net/base/host_resolver_impl.cc
diff --git a/net/base/host_resolver_impl.cc b/net/base/host_resolver_impl.cc
index d9330e213cebb1405002629e2fda5e6042329fac..02d20617be9bf20b33461cd2747335fe8f53042c 100644
--- a/net/base/host_resolver_impl.cc
+++ b/net/base/host_resolver_impl.cc
@@ -24,12 +24,14 @@
 #include "base/message_loop_proxy.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
+#include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
 #include "base/threading/worker_pool.h"
 #include "base/time.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
+#include "net/base/address_family.h"
 #include "net/base/address_list.h"
 #include "net/base/address_list_net_log_param.h"
 #include "net/base/dns_reloader.h"
@@ -38,6 +40,12 @@
 #include "net/base/net_errors.h"
 #include "net/base/net_log.h"
 #include "net/base/net_util.h"
+#include "net/dns/dns_config_service.h"
+#include "net/dns/dns_protocol.h"
+#include "net/dns/dns_response.h"
+#include "net/dns/dns_session.h"
+#include "net/dns/dns_transaction.h"
+#include "net/socket/client_socket_factory.h"
 
 #if defined(OS_WIN)
 #include "net/base/winsock_init.h"
@@ -54,6 +62,9 @@ const size_t kMaxHostLength = 4096;
 // Default TTL for successful resolutions with ProcTask.
 const unsigned kCacheEntryTTLSeconds = 60;
 
+// Default TTL for unsuccessful resolutions with ProcTask.
+const unsigned kNegativeCacheEntryTTLSeconds = 0;
+
 // Maximum of 8 concurrent resolver threads (excluding retries).
 // Some routers (or resolvers) appear to start to provide host-not-found if
 // too many simultaneous resolutions are pending.  This number needs to be
@@ -66,9 +77,9 @@ static const size_t kDefaultMaxProcTasks = 8u;
 //
 // However since we allocated the AddressList ourselves we can safely
 // do this optimization and avoid reallocating the list.
-void MutableSetPort(int port, AddressList* addrlist) {
+void MutableSetPort(int port, AddressList* addr_list) {
   struct addrinfo* mutable_head =
-      const_cast<struct addrinfo*>(addrlist->head());
+      const_cast<struct addrinfo*>(addr_list->head());
   SetPortForAllAddrinfos(mutable_head, port);
 }
 
@@ -144,22 +155,20 @@ class CallSystemHostResolverProc : public HostResolverProc {
   virtual int Resolve(const std::string& hostname,
                       AddressFamily address_family,
                       HostResolverFlags host_resolver_flags,
-                      AddressList* addrlist,
+                      AddressList* addr_list,
                       int* os_error) OVERRIDE {
     return SystemHostResolverProc(hostname,
                                   address_family,
                                   host_resolver_flags,
-                                  addrlist,
+                                  addr_list,
                                   os_error);
   }
 };
 
 // Extra parameters to attach to the NetLog when the resolve failed.
-class HostResolveFailedParams : public NetLog::EventParameters {
+class ProcTaskFailedParams : public NetLog::EventParameters {
  public:
-  HostResolveFailedParams(uint32 attempt_number,
-                          int net_error,
-                          int os_error)
+  ProcTaskFailedParams(uint32 attempt_number, int net_error, int os_error)
       : attempt_number_(attempt_number),
         net_error_(net_error),
         os_error_(os_error) {
@@ -201,6 +210,26 @@ class HostResolveFailedParams : public NetLog::EventParameters {
   const int os_error_;
 };
 
+// Extra parameters to attach to the NetLog when the DnsTask failed.
+class DnsTaskFailedParams : public NetLog::EventParameters {
+ public:
+  DnsTaskFailedParams(int net_error, int dns_error)
+      : net_error_(net_error), dns_error_(dns_error) {
+  }
+
+  virtual Value* ToValue() const OVERRIDE {
+    DictionaryValue* dict = new DictionaryValue();
+    dict->SetInteger("net_error", net_error_);
+    if (dns_error_)
+      dict->SetInteger("dns_error", dns_error_);
+    return dict;
+  }
+
+ private:
+  const int net_error_;
+  const int dns_error_;
+};
+
 // Parameters representing the information in a RequestInfo object, along with
 // the associated NetLog::Source.
 class RequestInfoParameters : public NetLog::EventParameters {
@@ -229,8 +258,7 @@ class RequestInfoParameters : public NetLog::EventParameters {
   const NetLog::Source source_;
 };
 
-// Parameters associated with the creation of a HostResolverImpl::Job
-// or a HostResolverImpl::ProcTask.
+// Parameters associated with the creation of a HostResolverImpl::Job.
 class JobCreationParameters : public NetLog::EventParameters {
  public:
   JobCreationParameters(const std::string& host,
@@ -290,14 +318,9 @@ void LogStartRequest(const BoundNetLog& source_net_log,
 void LogFinishRequest(const BoundNetLog& source_net_log,
                       const BoundNetLog& request_net_log,
                       const HostResolver::RequestInfo& info,
-                      int net_error,
-                      int os_error) {
-  scoped_refptr<NetLog::EventParameters> params;
-  if (net_error != OK) {
-    params = new HostResolveFailedParams(0, net_error, os_error);
-  }
-
-  request_net_log.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST, params);
+                      int net_error) {
+  request_net_log.EndEventWithNetErrorCode(
+      NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST, net_error);
   source_net_log.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL, NULL);
 }
 
@@ -315,8 +338,8 @@ void LogCancelRequest(const BoundNetLog& source_net_log,
 // Keeps track of the highest priority.
 class PriorityTracker {
  public:
-  PriorityTracker()
-      : highest_priority_(IDLE), total_count_(0) {
+  explicit PriorityTracker(RequestPriority priority)
+      : highest_priority_(priority), total_count_(0) {
     memset(counts_, 0, sizeof(counts_));
   }
 
@@ -361,7 +384,8 @@ class PriorityTracker {
 
 HostResolver* CreateHostResolver(size_t max_concurrent_resolves,
                                  size_t max_retry_attempts,
-                                 bool use_cache,
+                                 HostCache* cache,
+                                 scoped_ptr<DnsConfigService> config_service,
                                  NetLog* net_log) {
   if (max_concurrent_resolves == HostResolver::kDefaultParallelism)
     max_concurrent_resolves = kDefaultMaxProcTasks;
@@ -372,9 +396,10 @@ HostResolver* CreateHostResolver(size_t max_concurrent_resolves,
   PrioritizedDispatcher::Limits limits(NUM_PRIORITIES, max_concurrent_resolves);
 
   HostResolverImpl* resolver = new HostResolverImpl(
-      use_cache ? HostCache::CreateDefaultCache() : NULL,
+      cache,
       limits,
       HostResolverImpl::ProcTaskParams(NULL, max_retry_attempts),
+      config_service.Pass(),
       net_log);
 
   return resolver;
@@ -389,7 +414,8 @@ HostResolver* CreateSystemHostResolver(size_t max_concurrent_resolves,
                                        NetLog* net_log) {
   return CreateHostResolver(max_concurrent_resolves,
                             max_retry_attempts,
-                            true /* use_cache */,
+                            HostCache::CreateDefaultCache(),
+                            scoped_ptr<DnsConfigService>(NULL),
                             net_log);
 }
 
@@ -398,7 +424,21 @@ HostResolver* CreateNonCachingSystemHostResolver(size_t max_concurrent_resolves,
                                                  NetLog* net_log) {
   return CreateHostResolver(max_concurrent_resolves,
                             max_retry_attempts,
-                            false /* use_cache */,
+                            NULL,
+                            scoped_ptr<DnsConfigService>(NULL),
+                            net_log);
+}
+
+HostResolver* CreateAsyncHostResolver(size_t max_concurrent_resolves,
+                                      size_t max_retry_attempts,
+                                      NetLog* net_log) {
+  scoped_ptr<DnsConfigService> config_service =
+      DnsConfigService::CreateSystemService();
+  config_service->Watch();
+  return CreateHostResolver(max_concurrent_resolves,
+                            max_retry_attempts,
+                            HostCache::CreateDefaultCache(),
+                            config_service.Pass(),
                             net_log);
 }
 
@@ -440,9 +480,9 @@ class HostResolverImpl::Request {
   }
 
   // Prepare final AddressList and call completion callback.
-  void OnComplete(int error, const AddressList& addrlist) {
+  void OnComplete(int error, const AddressList& addr_list) {
     if (error == OK)
-      *addresses_ = CreateAddressListUsingPort(addrlist, info_.port());
+      *addresses_ = CreateAddressListUsingPort(addr_list, info_.port());
     CompletionCallback callback = callback_;
     MarkAsCanceled();
     callback.Run(error);
@@ -505,7 +545,8 @@ class HostResolverImpl::Request {
 class HostResolverImpl::ProcTask
     : public base::RefCountedThreadSafe<HostResolverImpl::ProcTask> {
  public:
-  typedef base::Callback<void(int, int, const AddressList&)> Callback;
+  typedef base::Callback<void(int net_error,
+                              const AddressList& addr_list)> Callback;
 
   ProcTask(const Key& key,
            const ProcTaskParams& params,
@@ -519,22 +560,14 @@ class HostResolverImpl::ProcTask
         completed_attempt_number_(0),
         completed_attempt_error_(ERR_UNEXPECTED),
         had_non_speculative_request_(false),
-        net_log_(BoundNetLog::Make(
-            job_net_log.net_log(),
-            NetLog::SOURCE_HOST_RESOLVER_IMPL_PROC_TASK)) {
+        net_log_(job_net_log) {
     if (!params_.resolver_proc)
       params_.resolver_proc = HostResolverProc::GetDefault();
     // If default is unset, use the system proc.
     if (!params_.resolver_proc)
       params_.resolver_proc = new CallSystemHostResolverProc();
 
-    job_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CREATE_PROC_TASK,
-                         new NetLogSourceParameter("source_dependency",
-                                                   net_log_.source()));
-
-    net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK,
-                        new JobCreationParameters(key_.hostname,
-                                                  job_net_log.source()));
+    net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK, NULL);
   }
 
   void Start() {
@@ -551,8 +584,6 @@ class HostResolverImpl::ProcTask
     if (was_canceled())
       return;
 
-    net_log_.AddEvent(NetLog::TYPE_CANCELLED, NULL);
-
     callback_.Reset();
 
     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK, NULL);
@@ -621,7 +652,6 @@ class HostResolverImpl::ProcTask
     AddressList results;
     int os_error = 0;
     // Running on the worker thread
-
     int error = params_.resolver_proc->Resolve(key_.hostname,
                                                key_.address_family,
                                                key_.host_resolver_flags,
@@ -657,14 +687,13 @@ class HostResolverImpl::ProcTask
     bool was_retry_attempt = attempt_number > 1;
 
     // Ideally the following code would be part of host_resolver_proc.cc,
-    // however it isn't safe to call NetworkChangeNotifier from worker
-    // threads. So we do it here on the IO thread instead.
+    // however it isn't safe to call NetworkChangeNotifier from worker threads.
+    // So we do it here on the IO thread instead.
     if (error != OK && NetworkChangeNotifier::IsOffline())
       error = ERR_INTERNET_DISCONNECTED;
 
-    // If this is the first attempt that is finishing later, then record
-    // data for the first attempt. Won't contaminate with retry attempt's
-    // data.
+    // If this is the first attempt that is finishing later, then record data
+    // for the first attempt. Won't contaminate with retry attempt's data.
     if (!was_retry_attempt)
       RecordPerformanceHistograms(start_time, error, os_error);
 
@@ -675,7 +704,7 @@ class HostResolverImpl::ProcTask
 
     scoped_refptr<NetLog::EventParameters> params;
     if (error != OK) {
-      params = new HostResolveFailedParams(attempt_number, error, os_error);
+      params = new ProcTaskFailedParams(attempt_number, error, os_error);
     } else {
       params = new NetLogIntegerParameter("attempt_number", attempt_number);
     }
@@ -696,13 +725,13 @@ class HostResolverImpl::ProcTask
     }
 
     if (error != OK) {
-      params = new HostResolveFailedParams(0, error, os_error);
+      params = new ProcTaskFailedParams(0, error, os_error);
     } else {
       params = new AddressListNetLogParam(results_);
     }
     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK, params);
 
-    callback_.Run(error, os_error, results_);
+    callback_.Run(error, results_);
   }
 
   void RecordPerformanceHistograms(const base::TimeTicks& start_time,
@@ -891,6 +920,8 @@ class HostResolverImpl::ProcTask
 //-----------------------------------------------------------------------------
 
 // Represents a request to the worker pool for a "probe for IPv6 support" call.
+//
+// TODO(szym): This could also be replaced with PostTaskAndReply and Callbacks.
 class HostResolverImpl::IPv6ProbeJob
     : public base::RefCountedThreadSafe<HostResolverImpl::IPv6ProbeJob> {
  public:
@@ -958,61 +989,130 @@ class HostResolverImpl::IPv6ProbeJob
 
 //-----------------------------------------------------------------------------
 
+// Resolves the hostname using DnsTransaction.
+// TODO(szym): This could be moved to separate source file as well.
+class HostResolverImpl::DnsTask {
+ public:
+  typedef base::Callback<void(int net_error,
+                              const AddressList& addr_list,
+                              base::TimeDelta ttl)> Callback;
+
+  DnsTask(DnsTransactionFactory* factory,
+          const Key& key,
+          const Callback& callback,
+          const BoundNetLog& job_net_log)
+      : callback_(callback), net_log_(job_net_log) {
+    DCHECK(factory);
+    DCHECK(!callback.is_null());
+
+    // For now we treat ADDRESS_FAMILY_UNSPEC as if it was IPV4.
+    uint16 qtype = (key.address_family == ADDRESS_FAMILY_IPV6)
+                   ? dns_protocol::kTypeAAAA
+                   : dns_protocol::kTypeA;
+    // TODO(szym): Implement "happy eyeballs".
+    transaction_ = factory->CreateTransaction(
+        key.hostname,
+        qtype,
+        base::Bind(&DnsTask::OnTransactionComplete, base::Unretained(this)),
+        net_log_);
+    DCHECK(transaction_.get());
+  }
+
+  int Start() {
+    net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK, NULL);
+    return transaction_->Start();
+  }
+
+  void OnTransactionComplete(DnsTransaction* transaction,
+                             int net_error,
+                             const DnsResponse* response) {
+    // TODO(szym): Record performance histograms.
+    // Run |callback_| last since the owning Job will then delete this DnsTask.
+    DnsResponse::Result result = DnsResponse::DNS_SUCCESS;
+    if (net_error == OK) {
+      AddressList addr_list;
+      base::TimeDelta ttl;
+      result = response->ParseToAddressList(&addr_list, &ttl);
+      if (result == DnsResponse::DNS_SUCCESS) {
+        net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
+                          new AddressListNetLogParam(addr_list));
+        callback_.Run(net_error, addr_list, ttl);
+        return;
+      }
+      net_error = ERR_DNS_MALFORMED_RESPONSE;
+    }
+    net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
+                      new DnsTaskFailedParams(net_error, result));
+    callback_.Run(net_error, AddressList(), base::TimeDelta());
+  }
+
+ private:
+  // The listener to the results of this DnsTask.
+  Callback callback_;
+
+  const BoundNetLog net_log_;
+
+  scoped_ptr<DnsTransaction> transaction_;
+};
+
+//-----------------------------------------------------------------------------
+
 // Aggregates all Requests for the same Key. Dispatched via PriorityDispatch.
-// Spawns ProcTask when started.
 class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
  public:
   // Creates new job for |key| where |request_net_log| is bound to the
-  // request that spawned it.
+  // request that spawned it and |priority| is the initial priority.
   Job(HostResolverImpl* resolver,
       const Key& key,
-      const BoundNetLog& request_net_log)
+      const BoundNetLog& request_net_log,
+      RequestPriority priority)
       : resolver_(resolver->AsWeakPtr()),
         key_(key),
+        priority_tracker_(priority),
         had_non_speculative_request_(false),
         net_log_(BoundNetLog::Make(request_net_log.net_log(),
-                                   NetLog::SOURCE_HOST_RESOLVER_IMPL_JOB)),
-        net_error_(ERR_IO_PENDING),
-        os_error_(0) {
+                                   NetLog::SOURCE_HOST_RESOLVER_IMPL_JOB)) {
     request_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CREATE_JOB, NULL);
 
     net_log_.BeginEvent(
         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
         make_scoped_refptr(new JobCreationParameters(
             key_.hostname, request_net_log.source())));
+
+    handle_ = resolver_->dispatcher_.Add(this, priority);
   }
 
   virtual ~Job() {
-    if (net_error_ == ERR_IO_PENDING) {
-      if (is_running()) {
-        DCHECK_EQ(ERR_IO_PENDING, net_error_);
+    if (is_running()) {
+      // |resolver_| was destroyed with this Job still in flight.
+      // Clean-up, record in the log, but don't run any callbacks.
+      if (is_proc_running()) {
         proc_task_->Cancel();
         proc_task_ = NULL;
-        net_error_ = ERR_ABORTED;
-      } else {
-        net_log_.AddEvent(NetLog::TYPE_CANCELLED, NULL);
-        net_error_ = OK;  // For NetLog.
       }
+      net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
+                                        ERR_ABORTED);
+    } else if (is_queued()) {
+      // This Job was cancelled without running.
+      // TODO(szym): is there's any benefit in having this distinction?
+      net_log_.AddEvent(NetLog::TYPE_CANCELLED, NULL);
+      net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB, NULL);
+    }
+    // else CompleteRequests logged EndEvent.
 
-      for (RequestsList::const_iterator it = requests_.begin();
-           it != requests_.end(); ++it) {
-        Request* req = *it;
-        if (req->was_canceled())
-          continue;
-        DCHECK_EQ(this, req->job());
-        LogCancelRequest(req->source_net_log(), req->request_net_log(),
-                         req->info());
-      }
+    // Log any remaining Requests as cancelled.
+    for (RequestsList::const_iterator it = requests_.begin();
+         it != requests_.end(); ++it) {
+      Request* req = *it;
+      if (req->was_canceled())
+        continue;
+      DCHECK_EQ(this, req->job());
+      LogCancelRequest(req->source_net_log(), req->request_net_log(),
+                       req->info());
     }
-    net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
-                                      net_error_);
     STLDeleteElements(&requests_);
   }
 
-  HostResolverImpl* resolver() const {
-    return resolver_;
-  }
-
   RequestPriority priority() const {
     return priority_tracker_.highest_priority();
   }
@@ -1026,26 +1126,14 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
     return key_;
   }
 
-  int net_error() const {
-    return net_error_;
-  }
-
-  // Used by HostResolverImpl with |dispatcher_|.
-  const PrioritizedDispatcher::Handle& handle() const {
-    return handle_;
-  }
-
-  void set_handle(const PrioritizedDispatcher::Handle& handle) {
-    handle_ = handle;
+  bool is_queued() const {
+    return !handle_.is_null();
   }
 
-  // The Job will own |req| and destroy it in ~Job.
-  void AddRequest(Request* req) {
+  void AddRequest(scoped_ptr<Request> req) {
     DCHECK_EQ(key_.hostname, req->info().hostname());
 
     req->set_job(this);
-    requests_.push_back(req);
-
     priority_tracker_.Add(req->info().priority());
 
     req->request_net_log().AddEvent(
@@ -1064,6 +1152,11 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
       if (proc_task_)
         proc_task_->set_had_non_speculative_request();
     }
+
+    requests_.push_back(req.release());
+
+    if (!handle_.is_null())
+      handle_ = resolver_->dispatcher_.ChangePriority(handle_, priority());
   }
 
   void CancelRequest(Request* req) {
@@ -1078,44 +1171,80 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_REQUEST_DETACH,
         make_scoped_refptr(new JobAttachParameters(
             req->request_net_log().source(), priority())));
+
+    if (!handle_.is_null()) {
+      if (num_active_requests() > 0) {
+        handle_ = resolver_->dispatcher_.ChangePriority(handle_, priority());
+      } else {
+        resolver_->dispatcher_.Cancel(handle_);
+        handle_.Reset();
+      }
+    }
   }
 
   // Aborts and destroys the job, completes all requests as aborted.
+  // The caller should clean up.
   void Abort() {
     // Job should only be aborted if it's running.
     DCHECK(is_running());
-    proc_task_->Cancel();
-    proc_task_ = NULL;
-    net_error_ = ERR_ABORTED;
-    os_error_ = 0;
-    CompleteRequests(AddressList());
+    if (is_proc_running()) {
+      proc_task_->Cancel();
+      proc_task_ = NULL;
+    }
+    dns_task_.reset();
+    CompleteRequests(ERR_ABORTED, AddressList(), base::TimeDelta());
   }
 
-  bool is_running() const {
+  bool is_dns_running() const {
+    return dns_task_.get() != NULL;
+  }
+
+  bool is_proc_running() const {
     return proc_task_.get() != NULL;
   }
 
+  bool is_running() const {
+    return is_dns_running() || is_proc_running();
+  }
+
   // Called by HostResolverImpl when this job is evicted due to queue overflow.
   void OnEvicted() {
     // Must not be running.
     DCHECK(!is_running());
-    handle_ = PrioritizedDispatcher::Handle();
+    handle_.Reset();
 
     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_EVICTED, NULL);
 
+    scoped_ptr<Job> self_deleter(this);
+    resolver_->RemoveJob(this);
+
     // This signals to CompleteRequests that this job never ran.
-    net_error_ = ERR_HOST_RESOLVER_QUEUE_TOO_LARGE;
-    os_error_ = 0;
-    CompleteRequests(AddressList());
+    CompleteRequests(ERR_HOST_RESOLVER_QUEUE_TOO_LARGE,
+                     AddressList(),
+                     base::TimeDelta());
   }
 
   // PriorityDispatch::Job interface.
   virtual void Start() OVERRIDE {
     DCHECK(!is_running());
-    handle_ = PrioritizedDispatcher::Handle();
+    handle_.Reset();
 
     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_STARTED, NULL);
 
+    if (resolver_->dns_transaction_factory_.get()) {
+      StartDnsTask();
+    } else {
+      StartProcTask();
+    }
+  }
+
+ private:
+  // TODO(szym): Since DnsTransaction does not consume threads, we can increase
+  // the limits on |dispatcher_|. But in order to keep the number of WorkerPool
+  // threads low, we will need to use an "inner" PrioritizedDispatcher with
+  // tighter limits.
+  void StartProcTask() {
+    DCHECK(!dns_task_.get());
     proc_task_ = new ProcTask(
         key_,
         resolver_->proc_params_,
@@ -1129,33 +1258,82 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
     proc_task_->Start();
   }
 
- private:
   // Called by ProcTask when it completes.
-  void OnProcTaskComplete(int net_error, int os_error,
-                          const AddressList& addrlist) {
-    DCHECK(is_running());
+  void OnProcTaskComplete(int net_error, const AddressList& addr_list) {
+    DCHECK(is_proc_running());
+    // |addr_list| will be destroyed once we destroy |proc_task_|.
+    AddressList list = addr_list;
     proc_task_ = NULL;
-    net_error_ = net_error;
-    os_error_ = os_error;
 
-    // We are the only consumer of |addrlist|, so we can safely change the port
-    // without copy-on-write. This pays off, when job has only one request.
-    AddressList list = addrlist;
-    if (net_error == OK && !requests_.empty())
-      MutableSetPort(requests_.front()->info().port(), &list);
-    CompleteRequests(list);
-  }
-
-  // Completes all Requests. Calls OnJobFinished and deletes self.
-  void CompleteRequests(const AddressList& addrlist) {
-    CHECK(resolver_);
+    base::TimeDelta ttl = base::TimeDelta::FromSeconds(
+        kNegativeCacheEntryTTLSeconds);
+    if (net_error == OK)
+      ttl = base::TimeDelta::FromSeconds(kCacheEntryTTLSeconds);
 
     // This job must be removed from resolver's |jobs_| now to make room for a
     // new job with the same key in case one of the OnComplete callbacks decides
     // to spawn one. Consequently, the job deletes itself when CompleteRequests
     // is done.
     scoped_ptr<Job> self_deleter(this);
-    resolver_->OnJobFinished(this, addrlist);
+    resolver_->OnJobFinished(this, net_error, list, ttl);
+
+    CompleteRequests(net_error, list, ttl);
+  }
+
+  void StartDnsTask() {
+    dns_task_.reset(new DnsTask(
+        resolver_->dns_transaction_factory_.get(),
+        key_,
+        base::Bind(&Job::OnDnsTaskComplete, base::Unretained(this)),
+        net_log_));
+
+    int rv = dns_task_->Start();
+    if (rv != ERR_IO_PENDING) {
+      DCHECK_NE(OK, rv);
+      dns_task_.reset();
+      StartProcTask();
+    }
+  }
+
+  // Called by DnsTask when it completes.
+  void OnDnsTaskComplete(int net_error,
+                         const AddressList& addr_list,
+                         base::TimeDelta ttl) {
+    DCHECK(is_dns_running());
+    // |addr_list| will be destroyed once we destroy |dns_task_|.
+    AddressList list = addr_list;
+    dns_task_.reset();
+
+    if (net_error != OK) {
+      // TODO(szym): Some net errors indicate lack of connectivity. Starting
+      // ProcTask in that case is a waste of time.
+      StartProcTask();
+      return;
+    }
+
+    // As in OnProcTaskComplete
+    scoped_ptr<Job> self_deleter(this);
+    resolver_->OnJobFinished(this, net_error, list, ttl);
+
+    CompleteRequests(net_error, list, ttl);
+  }
+
+  // Completes all Requests. Calls OnJobFinished and deletes self.
+  void CompleteRequests(int net_error,
+                        const AddressList& addr_list,
+                        base::TimeDelta ttl) {
+    CHECK(resolver_);
+    DCHECK(!is_running());
+    DCHECK(!is_queued());
+
+    // We are the only consumer of |addr_list|, so we can safely change the port
+    // without copy-on-write. This pays off, when job has only one request.
+    AddressList list = addr_list;
+    if (net_error == OK && !requests_.empty())
+      MutableSetPort(requests_.front()->info().port(), &list);
+
+    net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
+                                      net_error);
 
     // Complete all of the requests that were attached to the job.
     for (RequestsList::const_iterator it = requests_.begin();
@@ -1168,9 +1346,9 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
       DCHECK_EQ(this, req->job());
       // Update the net log and notify registered observers.
       LogFinishRequest(req->source_net_log(), req->request_net_log(),
-                       req->info(), net_error_, os_error_);
+                       req->info(), net_error);
 
-      req->OnComplete(net_error_, addrlist);
+      req->OnComplete(net_error, list);
 
       // Check if the resolver was destroyed as a result of running the
       // callback. If it was, we could continue, but we choose to bail.
@@ -1179,7 +1357,7 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
     }
   }
 
-  // Used to call OnJobFinished and RemoveJob.
+  // Used to call OnJobFinished.
   base::WeakPtr<HostResolverImpl> resolver_;
 
   Key key_;
@@ -1191,17 +1369,16 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
 
   BoundNetLog net_log_;
 
-  // Store result here in case the job fails fast in Resolve().
-  int net_error_;
-  int os_error_;
-
-  // A ProcTask created and started when this Job is dispatched..
+  // Resolves the host using a HostResolverProc.
   scoped_refptr<ProcTask> proc_task_;
 
+  // Resolves the host using a DnsTransaction.
+  scoped_ptr<DnsTask> dns_task_;
+
   // All Requests waiting for the result of this Job. Some can be canceled.
   RequestsList requests_;
 
-  // A handle used by HostResolverImpl in |dispatcher_|.
+  // A handle used by |HostResolverImpl::dispatcher_|.
   PrioritizedDispatcher::Handle handle_;
 };
 
@@ -1222,12 +1399,14 @@ HostResolverImpl::HostResolverImpl(
     HostCache* cache,
     const PrioritizedDispatcher::Limits& job_limits,
     const ProcTaskParams& proc_params,
+    scoped_ptr<DnsConfigService> dns_config_service,
     NetLog* net_log)
     : cache_(cache),
       dispatcher_(job_limits),
       max_queued_jobs_(job_limits.total_jobs * 100u),
       proc_params_(proc_params),
       default_address_family_(ADDRESS_FAMILY_UNSPECIFIED),
+      dns_config_service_(dns_config_service.Pass()),
       ipv6_probe_monitoring_(false),
       additional_resolver_flags_(0),
       net_log_(net_log) {
@@ -1254,6 +1433,9 @@ HostResolverImpl::HostResolverImpl(
 #endif
   NetworkChangeNotifier::AddDNSObserver(this);
 #endif
+
+  if (dns_config_service_.get())
+    dns_config_service_->AddObserver(this);
 }
 
 HostResolverImpl::~HostResolverImpl() {
@@ -1295,8 +1477,7 @@ int HostResolverImpl::Resolve(const RequestInfo& info,
 
   int rv = ResolveHelper(key, info, addresses, request_net_log);
   if (rv != ERR_DNS_CACHE_MISS) {
-    LogFinishRequest(source_net_log, request_net_log, info, rv,
-                     0  /* os_error (unknown since from cache) */);
+    LogFinishRequest(source_net_log, request_net_log, info, rv);
     return rv;
   }
 
@@ -1307,8 +1488,7 @@ int HostResolverImpl::Resolve(const RequestInfo& info,
   Job* job;
   if (jobit == jobs_.end()) {
     // Create new Job.
-    job = new Job(this, key, request_net_log);
-    job->set_handle(dispatcher_.Add(job, info.priority()));
+    job = new Job(this, key, request_net_log, info.priority());
 
     // Check for queue overflow.
     if (dispatcher_.num_queued_jobs() > max_queued_jobs_) {
@@ -1317,27 +1497,26 @@ int HostResolverImpl::Resolve(const RequestInfo& info,
       if (evicted == job) {
         delete job;
         rv = ERR_HOST_RESOLVER_QUEUE_TOO_LARGE;
-        LogFinishRequest(source_net_log, request_net_log, info, rv, 0);
+        LogFinishRequest(source_net_log, request_net_log, info, rv);
         return rv;
       }
       evicted->OnEvicted();  // Deletes |evicted|.
     }
-
     jobs_.insert(jobit, std::make_pair(key, job));
   } else {
     job = jobit->second;
   }
 
   // Can't complete synchronously. Create and attach request.
-  Request* req = new Request(source_net_log, request_net_log, info, callback,
-                             addresses);
-  job->AddRequest(req);
-  if (!job->handle().is_null())
-    job->set_handle(dispatcher_.ChangePriority(job->handle(), job->priority()));
+  scoped_ptr<Request> req(new Request(source_net_log,
+                                      request_net_log,
+                                      info,
+                                      callback,
+                                      addresses));
   if (out_req)
-    *out_req = reinterpret_cast<RequestHandle>(req);
+    *out_req = reinterpret_cast<RequestHandle>(req.get());
 
-  DCHECK_EQ(ERR_IO_PENDING, job->net_error());
+  job->AddRequest(req.Pass());
   // Completion happens during Job::CompleteRequests().
   return ERR_IO_PENDING;
 }
@@ -1376,8 +1555,7 @@ int HostResolverImpl::ResolveFromCache(const RequestInfo& info,
   Key key = GetEffectiveKeyForRequest(info);
 
   int rv = ResolveHelper(key, info, addresses, request_net_log);
-  LogFinishRequest(source_net_log, request_net_log, info, rv,
-                   0  /* os_error (unknown since from cache) */);
+  LogFinishRequest(source_net_log, request_net_log, info, rv);
   return rv;
 }
 
@@ -1391,23 +1569,14 @@ void HostResolverImpl::CancelRequest(RequestHandle req_handle) {
 
   job->CancelRequest(req);
 
-  if (!job->handle().is_null()) {
-    // Still in queue.
-    if (job->num_active_requests()) {
-      job->set_handle(dispatcher_.ChangePriority(job->handle(),
-                                                 job->priority()));
-    } else {
-      dispatcher_.Cancel(job->handle());
-      RemoveJob(job);
-      delete job;
-    }
-  } else {
-    // Job is running (and could be in CompleteRequests right now).
-    // But to be in Request::OnComplete we would have to have a non-canceled
-    // request. So it is safe to Abort it if it has no more active requests.
-    if (!job->num_active_requests()) {
+  if (job->num_active_requests() == 0) {
+    // If we were called from a Requests' callback within Job::CompleteRequests,
+    // that Request could not have been cancelled, so job->num_active_requests()
+    // could not be 0. Therefore, we are not in Job::CompleteRequests().
+    RemoveJob(job);
+    if (job->is_running())
       job->Abort();
-    }
+    delete job;
   }
 }
 
@@ -1482,23 +1651,21 @@ bool HostResolverImpl::ServeFromCache(const Key& key,
   return true;
 }
 
-void HostResolverImpl::OnJobFinished(Job* job, const AddressList& addrlist) {
+void HostResolverImpl::OnJobFinished(Job* job,
+                                     int net_error,
+                                     const AddressList& addr_list,
+                                     base::TimeDelta ttl) {
   DCHECK(job);
-  DCHECK(job->handle().is_null());
-  RemoveJob(job);
-  if (job->net_error() == ERR_HOST_RESOLVER_QUEUE_TOO_LARGE)
-    return;
+  DCHECK(!job->is_queued());
+  DCHECK_NE(ERR_HOST_RESOLVER_QUEUE_TOO_LARGE, net_error);
+  DCHECK_NE(ERR_ABORTED, net_error);
 
+  RemoveJob(job);
   // Signal dispatcher that a slot has opened.
   dispatcher_.OnJobFinished();
-  if (job->net_error() == ERR_ABORTED)
-    return;
   // Write result to the cache.
   if (cache_.get()) {
-    base::TimeDelta ttl = base::TimeDelta::FromSeconds(0);
-    if (job->net_error() == OK)
-      ttl = base::TimeDelta::FromSeconds(kCacheEntryTTLSeconds);
-    cache_->Set(job->key(), job->net_error(), addrlist,
+    cache_->Set(job->key(), net_error, addr_list,
                 base::TimeTicks::Now(), ttl);
   }
 }
@@ -1545,21 +1712,26 @@ HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
 
 void HostResolverImpl::AbortAllInProgressJobs() {
   base::WeakPtr<HostResolverImpl> self = AsWeakPtr();
-  // Scan |jobs_| for running jobs and abort them.
+  // In Abort, a Request callback could spawn new Jobs with matching keys, so
+  // first collect and remove all running jobs from |jobs_|.
+  std::vector<Job*> jobs_to_abort;
   for (JobMap::iterator it = jobs_.begin(); it != jobs_.end(); ) {
     Job* job = it->second;
-    // Advance the iterator before we might erase it.
-    ++it;
     if (job->is_running()) {
-      job->Abort();
-      // Check if resolver was deleted in a request callback.
-      if (!self)
-        return;
+      jobs_to_abort.push_back(job);
+      jobs_.erase(it++);
     } else {
-      // Keep it in |dispatch_|.
-      DCHECK(!job->handle().is_null());
+      DCHECK(job->is_queued());
+      ++it;
     }
   }
+
+  // Then Abort them and dispatch new Jobs.
+  for (size_t i = 0; i < jobs_to_abort.size(); ++i) {
+    jobs_to_abort[i]->Abort();
+    dispatcher_.OnJobFinished();
+  }
+  STLDeleteElements(&jobs_to_abort);
 }
 
 void HostResolverImpl::OnIPAddressChanged() {
@@ -1594,4 +1766,23 @@ void HostResolverImpl::OnDNSChanged() {
   // |this| may be deleted inside AbortAllInProgressJobs().
 }
 
+void HostResolverImpl::OnConfigChanged(const DnsConfig& dns_config) {
+  // We want a new factory in place, before we Abort running Jobs, so that the
+  // newly started jobs use the new factory.
+  bool had_factory = (dns_transaction_factory_.get() != NULL);
+  if (dns_config.IsValid()) {
+    dns_transaction_factory_ = DnsTransactionFactory::CreateFactory(
+        new DnsSession(dns_config,
+                       ClientSocketFactory::GetDefaultFactory(),
+                       base::Bind(&base::RandInt),
+                       net_log_));
+  } else {
+    dns_transaction_factory_.reset();
+  }
+  // Don't Abort running Jobs unless they were running on DnsTransaction.
+  // TODO(szym): This will change once http://crbug.com/114827 is fixed.
+  if (had_factory)
+    OnDNSChanged();
+}
+
 }  // namespace net