Change HostResolver::Resolve() to take an std::unique_ptr<Request>* rather than a RequestHandle*

net/proxy/proxy_resolver_v8_tracing.cc

Index: net/proxy/proxy_resolver_v8_tracing.cc
diff --git a/net/proxy/proxy_resolver_v8_tracing.cc b/net/proxy/proxy_resolver_v8_tracing.cc
index ef25fc80ece4bdbfa1fff4cf64a88c313bc5bb75..6bee71dec16a0b405b30f7386b81e22840a03a6e 100644
--- a/net/proxy/proxy_resolver_v8_tracing.cc
+++ b/net/proxy/proxy_resolver_v8_tracing.cc
@@ -284,7 +284,7 @@ class Job : public base::RefCountedThreadSafe<Job>,
   // Handle to the outstanding request in the HostResolver, or NULL.
   // This is mutated and used on the origin thread, however it may be read by
   // the worker thread for some DCHECKS().
-  HostResolver::RequestHandle pending_dns_;
+  std::unique_ptr<HostResolver::Request> pending_dns_;

[jochen (gone - plz use gerrit), 2017/03/08 15:22:10]

std::unique_ptr cannot be read atomically, and given that we read it lock-less
from workers while writing (in Job::Cancel) from the foreground thread, this now
introduces a data race

 
   // Indicates if the outstanding DNS request completed synchronously. Written
   // on the origin thread, and read by the worker thread.
@@ -338,8 +338,7 @@ Job::Job(const Job::Params* params,
       bindings_(std::move(bindings)),
       event_(base::WaitableEvent::ResetPolicy::MANUAL,
              base::WaitableEvent::InitialState::NOT_SIGNALED),
-      last_num_dns_(0),
-      pending_dns_(NULL) {
+      last_num_dns_(0) {
   CheckIsOnOriginThread();
 }
 
@@ -394,10 +393,7 @@ void Job::Cancel() {
 
   ReleaseCallback();
 
-  if (pending_dns_) {
-    host_resolver()->CancelRequest(pending_dns_);
-    pending_dns_ = NULL;
-  }
+  pending_dns_.reset();
 
   // The worker thread might be blocked waiting for DNS.
   event_.Signal();
@@ -710,7 +706,7 @@ void Job::DoDnsOperation() {
   if (cancelled_.IsSet())
     return;
 
-  HostResolver::RequestHandle dns_request = NULL;
+  std::unique_ptr<HostResolver::Request> dns_request;
   int result = host_resolver()->Resolve(
       MakeDnsRequestInfo(pending_dns_host_, pending_dns_op_), DEFAULT_PRIORITY,
       &pending_dns_addresses_, base::Bind(&Job::OnDnsOperationComplete, this),
@@ -728,7 +724,7 @@ void Job::DoDnsOperation() {
     OnDnsOperationComplete(result);
   } else {
     DCHECK(dns_request);
-    pending_dns_ = dns_request;
+    pending_dns_ = std::move(dns_request);
     // OnDnsOperationComplete() will be called by host resolver on completion.
   }
 
@@ -747,7 +743,7 @@ void Job::OnDnsOperationComplete(int result) {
 
   SaveDnsToLocalCache(pending_dns_host_, pending_dns_op_, result,
                       pending_dns_addresses_);
-  pending_dns_ = NULL;
+  pending_dns_.reset();
 
   if (blocking_dns_) {
     event_.Signal();