Record field-trial information in stability file for crash analysis.

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"
 #include "base/build_time.h"
 #include "base/command_line.h"
+#include "base/debug/activity_tracker.h"
 #include "base/logging.h"
 #include "base/metrics/field_trial_param_associator.h"
 #include "base/process/memory.h"
 #include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 
 // On POSIX, the fd is shared using the mapping in GlobalDescriptors.
@@ skipping 952 matching lines @@
       return;
     field_trial->group_reported_ = true;
 
     if (!field_trial->enable_field_trial_)
       return;
 
     if (kUseSharedMemoryForFieldTrials)
       ActivateFieldTrialEntryWhileLocked(field_trial);
   }
 
+  // Recording for stability debugging has to be done inline as a task posted
+  // to an observer may not get executed before a crash.

[Alexei Svitkine (slow), 2017/02/06 17:46:12]

While you're changing this, how about setting crash_keys from the same place?
This way, the problem will also be fixed there too.

[manzagop (departed), 2017/02/06 18:38:16]

IIUC the problem with crash keys is the update leads to querying for all active
experiments, hashing them, and formatting them, which is deemed too expensive to
be inline experiment activation?

[bcwhite, 2017/02/07 15:58:58]

Happy to do it, if it's desired, but I'll do it as a separate CL so if there is
a problem and it has to be reverted, it won't affect the rest.

+  base::debug::GlobalActivityTracker::RecordFieldTrial(

[Alexei Svitkine (slow), 2017/02/06 17:46:12]

Is this API thread safe? Because this can be called from any thread....

If it is, please document it in the API's function comment.

[bcwhite, 2017/02/07 15:58:59]

Yes.  Done.

+      field_trial->trial_name(), field_trial->group_name_internal());
+
   global_->observer_list_->Notify(
       FROM_HERE, &FieldTrialList::Observer::OnFieldTrialGroupFinalized,
       field_trial->trial_name(), field_trial->group_name_internal());
 }
 
 // static
 size_t FieldTrialList::GetFieldTrialCount() {
   if (!global_)
     return 0;
   AutoLock auto_lock(global_->lock_);
@@ skipping 352 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