chromium之tracked_objects

// For each thread, we have a ThreadData that stores all tracking info generated
// on this thread.  This prevents the need for locking as data accumulates.

该文件用到了chromium之ThreadLocalStorage

看看头文件

class ThreadData {
 public:
  typedef std::map<Location, Births*> BirthMap;
  typedef std::map<const Births*, DeathData> DeathMap;
 
  ThreadData();
 
  // Using Thread Local Store, find the current instance for collecting data.
  // If an instance does not exist, construct one (and remember it for use on
  // this thread.
  // If shutdown has already started, and we don't yet have an instance, then
  // return null.
  static ThreadData* current();
 
  // For a given about:objects URL, develop resulting HTML, and append to
  // output.
  static void WriteHTML(const std::string& query, std::string* output);
 
  // For a given accumulated array of results, use the comparator to sort and
  // subtotal, writing the results to the output.
  static void WriteHTMLTotalAndSubtotals(
      const DataCollector::Collection& match_array,
      const Comparator& comparator, std::string* output);
 
  // In this thread's data, find a place to record a new birth.
  Births* FindLifetime(const Location& location);
 
  // Find a place to record a death on this thread.
  void TallyADeath(const Births& lifetimes, const base::TimeDelta& duration);
 
  // (Thread safe) Get start of list of instances.
  static ThreadData* first();
  // Iterate through the null terminated list of instances.
  ThreadData* next() const { return next_; }
 
  MessageLoop* message_loop() const { return message_loop_; }
  const std::string ThreadName() const;
 
  // Using our lock, make a copy of the specified maps.  These calls may arrive
  // from non-local threads.
  void SnapshotBirthMap(BirthMap *output) const;
  void SnapshotDeathMap(DeathMap *output) const;
 
  static void RunOnAllThreads(void (*Func)());
 
  // Set internal status_ to either become ACTIVE, or later, to be SHUTDOWN,
  // based on argument being true or false respectively.
  // IF tracking is not compiled in, this function will return false.
  static bool StartTracking(bool status);
  static bool IsActive();
 
#ifdef OS_WIN
  // WARNING: ONLY call this function when all MessageLoops are still intact for
  // all registered threads.  IF you call it later, you will crash.
  // Note: You don't need to call it at all, and you can wait till you are
  // single threaded (again) to do the cleanup via
  // ShutdownSingleThreadedCleanup().
  // Start the teardown (shutdown) process in a multi-thread mode by disabling
  // further additions to thread database on all threads.  First it makes a
  // local (locked) change to prevent any more threads from registering.  Then
  // it Posts a Task to all registered threads to be sure they are aware that no
  // more accumulation can take place.
  static void ShutdownMultiThreadTracking();
#endif
 
  // WARNING: ONLY call this function when you are running single threaded
  // (again) and all message loops and threads have terminated.  Until that
  // point some threads may still attempt to write into our data structures.
  // Delete recursively all data structures, starting with the list of
  // ThreadData instances.
  static void ShutdownSingleThreadedCleanup();

大致想想怎么用

1. 开始

开始运行，

StartTracking(true)

2. 结束，并输出

StartTracking(false)

WriteHTML(...)
 
有个测试用例，可以看看

TEST_F(TrackedObjectsTest, MinimalStartupShutdown) {
  // Minimal test doesn't even create any tasks.
  if (!ThreadData::StartTracking(true))
    return;
 
  EXPECT_FALSE(ThreadData::first());  // No activity even on this thread.
  ThreadData* data = ThreadData::current();
  EXPECT_TRUE(ThreadData::first());  // Now class was constructed.
  EXPECT_TRUE(data);
  EXPECT_TRUE(!data->next());
  EXPECT_EQ(data, ThreadData::current());
  ThreadData::BirthMap birth_map;
  data->SnapshotBirthMap(&birth_map); // Get all birth data
  EXPECT_EQ(0u, birth_map.size());
  ThreadData::DeathMap death_map;
  data->SnapshotDeathMap(&death_map);
  EXPECT_EQ(0u, death_map.size());
  ThreadData::ShutdownSingleThreadedCleanup();
 
  // Do it again, just to be sure we reset state completely.
  ThreadData::StartTracking(true);
  EXPECT_FALSE(ThreadData::first());  // No activity even on this thread.
  data = ThreadData::current();
  EXPECT_TRUE(ThreadData::first());  // Now class was constructed.
  EXPECT_TRUE(data);
  EXPECT_TRUE(!data->next());
  EXPECT_EQ(data, ThreadData::current());
  birth_map.clear();
  data->SnapshotBirthMap(&birth_map);
  EXPECT_EQ(0u, birth_map.size());
  death_map.clear();
  data->SnapshotDeathMap(&death_map);
  EXPECT_EQ(0u, death_map.size());
  ThreadData::ShutdownSingleThreadedCleanup();
}