Initial implementation for sharing field trial state (win)

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 46 matching lines @@
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
+#include "base/command_line.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/shared_memory.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/strings/string_piece.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class FieldTrialList;
 
 class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
@@ skipping 377 matching lines @@
   // used in a non-browser process, to carry randomly selected state in a
   // browser process into this non-browser process, but could also be invoked
   // through a command line argument to the browser process. Created field
   // trials will be marked "used" for the purposes of active trial reporting
   // if they are prefixed with |kActivationMarker|. Trial names in
   // |ignored_trial_names| are ignored when parsing |trials_string|.
   static bool CreateTrialsFromString(
       const std::string& trials_string,
       const std::set<std::string>& ignored_trial_names);
 
+  // If using shared memory to pass around the list of field trials, then

[Alexei Svitkine (slow), 2016/10/06 13:45:30]

The first sentence should describe what the function does. Then, you can go into
details of how the args work.

[lawrencewu, 2016/10/06 20:14:57]

Done.

+  // expects |field_trial_handle_switch| argument to
+  // contain the shared memory handle, and it opens the handle, reads the memory
+  // and creates the trials.
+  // If not, then create the trials as before (using the kForceFieldTrials
+  // switch). Needs the |field_trial_handle_switch| argument to be passed in
+  // since base/ can't depend on content.
+  static void CreateTrialsFromCommandLine(
+      const base::CommandLine cmd_line,

[Alexei Svitkine (slow), 2016/10/06 13:45:30]

Pass by const& - otherwise you're copying the object. Here and in the .cc file.

[lawrencewu, 2016/10/06 20:14:57]

Done.

+      const char* field_trial_handle_switch);
+
+  // Adds a switch to the command line containing the field trial state as a
+  // string (if not using shared memory to share field trial state), or the
+  // shared memory handle + length.
+  // Needs the |field_trial_handle_switch| argument to be passed in since base/
+  // can't depend on content.
+  static std::unique_ptr<base::SharedMemory> CopyFieldTrialStateToSharedMemory(
+      base::CommandLine* cmd_line,
+      const char* field_trial_handle_switch);
+
   // Create a FieldTrial with the given |name| and using 100% probability for
   // the FieldTrial, force FieldTrial to have the same group string as
   // |group_name|. This is commonly used in a non-browser process, to carry
   // randomly selected state in a browser process into this non-browser process.
   // It returns NULL if there is a FieldTrial that is already registered with
   // the same |name| but has different finalized group string (|group_name|).
   static FieldTrial* CreateFieldTrial(const std::string& name,
                                       const std::string& group_name);
 
   // Add an observer to be notified when a field trial is irrevocably committed
@@ skipping 47 matching lines @@
 
   // List of observers to be notified when a group is selected for a FieldTrial.
   scoped_refptr<ObserverListThreadSafe<Observer> > observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_FIELD_TRIAL_H_