Fix deadlock issue with AllStatesToString

base/metrics/field_trial.h

 // 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.
 
 // FieldTrial is a class for handling details of statistical experiments
 // performed by actual users in the field (i.e., in a shipped or beta product).
 // All code is called exclusively on the UI thread currently.
 //
 // The simplest example is an experiment to see whether one of two options
 // produces "better" results across our user population.  In that scenario, UMA
@@ skipping 233 matching lines @@
   void SetTrialRegistered();
 
   // Sets the chosen group name and number.
   void SetGroupChoice(const std::string& group_name, int number);
 
   // Ensures that a group is chosen, if it hasn't yet been. The field trial
   // might yet be disabled, so this call will *not* notify observers of the
   // status.
   void FinalizeGroupChoice();
 
+  // Implements FinalizeGroupChoice() with the added flexibility of being
+  // deadlock-free if |is_locked| is true and the caller is holding a lock.
+  void FinalizeGroupChoiceImpl(bool is_locked);
+
   // Returns the trial name and selected group name for this field trial via
   // the output parameter |active_group|, but only if the group has already
   // been chosen and has been externally observed via |group()| and the trial
   // has not been disabled. In that case, true is returned and |active_group|
   // is filled in; otherwise, the result is false and |active_group| is left
   // untouched.
   bool GetActiveGroup(ActiveGroup* active_group) const;
 
   // Returns the trial name and selected group name for this field trial via
   // the output parameter |field_trial_state|, but only if the trial has not
   // been disabled. In that case, true is returned and |field_trial_state| is
   // filled in; otherwise, the result is false and |field_trial_state| is left
   // untouched.
   bool GetState(State* field_trial_state);
 
+  // Does the same thing as above, but is deadlock-free if the caller is holding
+  // a lock.
+  bool GetStateWhileLocked(State* field_trial_state);
+
   // Returns the group_name. A winner need not have been chosen.
   std::string group_name_internal() const { return group_name_; }
 
   // The name of the field trial, as can be found via the FieldTrialList.
   const std::string trial_name_;
 
   // The maximum sum of all probabilities supplied, which corresponds to 100%.
   // This is the scaling factor used to adjust supplied probabilities.
   const Probability divisor_;
 
@@ skipping 231 matching lines @@
                                       const std::string& group_name);
 
   // Add an observer to be notified when a field trial is irrevocably committed
   // to being part of some specific field_group (and hence the group_name is
   // also finalized for that field_trial).
   static void AddObserver(Observer* observer);
 
   // Remove an observer.
   static void RemoveObserver(Observer* observer);
 
-  // Grabs the lock and adds the field trial to the allocator. This should only
-  // be called from FinalizeGroupChoice().
-  static void OnGroupFinalized(FieldTrial* field_trial);
+  // Grabs the lock if necessary and adds the field trial to the allocator. This
+  // should only be called from FinalizeGroupChoice().
+  static void OnGroupFinalized(bool is_locked, FieldTrial* field_trial);
 
   // Notify all observers that a group has been finalized for |field_trial|.
   static void NotifyFieldTrialGroupSelection(FieldTrial* field_trial);
 
   // Return the number of active field trials.
   static size_t GetFieldTrialCount();
 
  private:
   // Allow tests to access our innards for testing purposes.
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, InstantiateAllocator);
@@ skipping 67 matching lines @@
   // AppendFieldTrialHandleIfNeeded().
   HANDLE readonly_allocator_handle_ = nullptr;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_FIELD_TRIAL_H_