Actually update FieldTrialEntry's activated field

base/metrics/field_trial.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/field_trial.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/base_switches.h"
@@ skipping 291 matching lines @@
     : trial_name_(trial_name),
       divisor_(total_probability),
       default_group_name_(default_group_name),
       random_(GetGroupBoundaryValue(total_probability, entropy_value)),
       accumulated_group_probability_(0),
       next_group_number_(kDefaultGroupNumber + 1),
       group_(kNotFinalized),
       enable_field_trial_(true),
       forced_(false),
       group_reported_(false),
-      trial_registered_(false) {
+      trial_registered_(false),
+      ref_(SharedPersistentMemoryAllocator::kReferenceNull) {
   DCHECK_GT(total_probability, 0);
   DCHECK(!trial_name_.empty());
   DCHECK(!default_group_name_.empty());
 }
 
 FieldTrial::~FieldTrial() {}
 
 void FieldTrial::SetTrialRegistered() {
   DCHECK_EQ(kNotFinalized, group_);
   DCHECK(!trial_registered_);
@@ skipping 10 matching lines @@
 }
 
 void FieldTrial::FinalizeGroupChoice() {
   if (group_ != kNotFinalized)
     return;
   accumulated_group_probability_ = divisor_;
   // Here it's OK to use |kDefaultGroupNumber| since we can't be forced and not
   // finalized.
   DCHECK(!forced_);
   SetGroupChoice(default_group_name_, kDefaultGroupNumber);
+
+  // Add the field trial to shared memory.
+  if (kUseSharedMemoryForFieldTrials) {
+    SharedPersistentMemoryAllocator* allocator =
+        FieldTrialList::GetFieldTrialAllocator();

[Alexei Svitkine (slow), 2016/10/25 19:18:53]

I'm not a fan of having a public getter for the allocator - since that means
anyone can get it and mess with it.

So, to avoid this, let's turn add a static function on FieldTrialList for it.

Note: It can be a wrapper around AddToAllocatorWhileLocked() since that function
requires the caller to hold the lock (which I think you currently don't and so
need to fix anyway) and then it can just access the allocator.

[lawrencewu, 2016/10/25 20:27:33]

I moved the AddToAllocatorWhileLocked function to be a static function on
FieldTrialList, and it now holds its own lock.

+    this->AddToAllocatorWhileLocked(allocator);
+  }
 }
 
 bool FieldTrial::GetActiveGroup(ActiveGroup* active_group) const {
   if (!group_reported_ || !enable_field_trial_)
     return false;
   DCHECK_NE(group_, kNotFinalized);
   active_group->trial_name = trial_name_;
   active_group->group_name = group_name_;
   return true;
 }
@@ skipping 426 matching lines @@
   {
     AutoLock auto_lock(global_->lock_);
     if (field_trial->group_reported_)
       return;
     field_trial->group_reported_ = true;
 
     if (!field_trial->enable_field_trial_)
       return;
 
     if (kUseSharedMemoryForFieldTrials) {
-      field_trial->AddToAllocatorWhileLocked(
-          global_->field_trial_allocator_.get());
+      SharedPersistentMemoryAllocator* allocator =

[Alexei Svitkine (slow), 2016/10/25 19:18:53]

Nit: Please make a helper function for this block of code.

[lawrencewu, 2016/10/25 20:27:33]

Done.

+          global_->field_trial_allocator_.get();
+      SharedPersistentMemoryAllocator::Reference ref = field_trial->ref_;
+      if (ref == SharedPersistentMemoryAllocator::kReferenceNull) {
+        // It's fine to do this even if the allocator hasn't been instantiated
+        // yet -- it'll just return early.
+        field_trial->AddToAllocatorWhileLocked(allocator);
+      } else {
+        FieldTrialEntry* entry =
+            allocator->GetAsObject<FieldTrialEntry>(ref, kFieldTrialType);
+        entry->activated = true;
+      }
     }
   }
 
   global_->observer_list_->Notify(
       FROM_HERE, &FieldTrialList::Observer::OnFieldTrialGroupFinalized,
       field_trial->trial_name(), field_trial->group_name_internal());
 }
 
 #if !defined(OS_NACL)
 // static
@@ skipping 27 matching lines @@
 #endif
 }
 #endif
 
 void FieldTrial::AddToAllocatorWhileLocked(
     SharedPersistentMemoryAllocator* allocator) {
   // Don't do anything if the allocator hasn't been instantiated yet.
   if (allocator == nullptr)
     return;
 
+  // Or if we've already added it.
+  if (ref_ != SharedPersistentMemoryAllocator::kReferenceNull)
+    return;
+
   State trial_state;
   if (!GetState(&trial_state))
     return;
 
   size_t trial_name_size = trial_state.trial_name.size() + 1;
   size_t group_name_size = trial_state.group_name.size() + 1;
   size_t size = sizeof(FieldTrialEntry) + trial_name_size + group_name_size;
 
   // Allocate just enough memory to fit the FieldTrialEntry struct, trial name,
   // and group name.
@@ skipping 14 matching lines @@
   char* trial_name = reinterpret_cast<char*>(entry) + trial_name_offset;
   char* group_name = reinterpret_cast<char*>(entry) + group_name_offset;
   memcpy(trial_name, trial_state.trial_name.data(), trial_name_size);
   memcpy(group_name, trial_state.group_name.data(), group_name_size);
 
   // Null terminate the strings.
   trial_name[trial_state.trial_name.size()] = '\0';
   group_name[trial_state.group_name.size()] = '\0';
 
   allocator->MakeIterable(ref);
+  ref_ = ref;
 }
 
 // static
 size_t FieldTrialList::GetFieldTrialCount() {
   if (!global_)
     return 0;
   AutoLock auto_lock(global_->lock_);
   return global_->registered_.size();
 }
 
 // static
+SharedPersistentMemoryAllocator* FieldTrialList::GetFieldTrialAllocator() {
+  return global_->field_trial_allocator_.get();
+}
+
+// static
 const FieldTrial::EntropyProvider*
     FieldTrialList::GetEntropyProviderForOneTimeRandomization() {
   if (!global_) {
     used_without_global_ = true;
     return NULL;
   }
 
   return global_->entropy_provider_.get();
 }
 
@@ skipping 11 matching lines @@
     return;
   }
   AutoLock auto_lock(global_->lock_);
   CHECK(!global_->PreLockedFind(trial->trial_name())) << trial->trial_name();
   trial->AddRef();
   trial->SetTrialRegistered();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base