Hold allocator lock while fetching 'used' count.

base/debug/activity_tracker_unittest.cc

 // Copyright 2016 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/debug/activity_tracker.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/files/file.h"
@@ skipping 56 matching lines @@
     if (!global_tracker)
       return 0;
     return global_tracker->thread_tracker_count_.load(
         std::memory_order_relaxed);
   }
 
   size_t GetGlobalInactiveTrackerCount() {
     GlobalActivityTracker* global_tracker = GlobalActivityTracker::Get();
     if (!global_tracker)
       return 0;
+    base::AutoLock autolock(global_tracker->thread_tracker_allocator_lock_);
     return global_tracker->thread_tracker_allocator_.cache_used();
   }
 
   static void DoNothing() {}
 };
 
 TEST_F(ActivityTrackerTest, PushPopTest) {
   std::unique_ptr<ThreadActivityTracker> tracker = CreateActivityTracker();
   ActivitySnapshot snapshot;
 
@@ skipping 194 matching lines @@
   EXPECT_EQ(starting_inactive, GetGlobalInactiveTrackerCount());
 
   t2.Exit();
   t2.Join();
   EXPECT_EQ(starting_active, GetGlobalActiveTrackerCount());
   EXPECT_EQ(starting_inactive + 1, GetGlobalInactiveTrackerCount());
 }
 
 }  // namespace debug
 }  // namespace base