Introduce TraceLog::AsyncEnabledStateObserver

base/trace_event/trace_log.cc

 // Copyright 2015 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/trace_event/trace_log.h"
 
 #include <algorithm>
 #include <cmath>
 #include <memory>
 #include <utility>
@@ skipping 315 matching lines @@
 
   trace_log_->lock_.AssertAcquired();
   if (trace_log_->CheckGeneration(generation_)) {
     // Return the chunk to the buffer only if the generation matches.
     trace_log_->logged_events_->ReturnChunk(chunk_index_, std::move(chunk_));
   }
   // Otherwise this method may be called from the destructor, or TraceLog will
   // find the generation mismatch and delete this buffer soon.
 }
 
+struct TraceLog::RegisteredThreadSafeObserver {
+  RegisteredThreadSafeObserver(WeakPtr<ThreadSafeEnabledStateObserver> observer)
+      : observer_(observer), task_runner_(ThreadTaskRunnerHandle::Get()) {}
+
+  ~RegisteredThreadSafeObserver() {}
+
+  WeakPtr<ThreadSafeEnabledStateObserver> observer_;

[Primiano Tucci (use gerrit), 2016/05/09 17:18:29]

nit since this is an internal struct, and you are directly using its fields
(makes sense) these names should be without final underscore.

From [1] "Data members of structs, both static and non-static, are named like
ordinary nonmember variables. They do not have the trailing underscores that
data members in classes have."

[1] https://google.github.io/styleguide/cppguide.html#Variable_Names

[Xiaocheng, 2016/05/10 09:33:33]

Done.

+  scoped_refptr<TaskRunner> task_runner_;

[Primiano Tucci (use gerrit), 2016/05/09 17:18:29]

Can you s/TaskRunner/SequencedTaskRunner/. It will not make any practical
difference in this CL. It's purely for documentation/reasoning purposes: you
need a sequencing TR if you want to guarantee that you can't race on
destruction.

[Xiaocheng, 2016/05/10 09:33:33]

Done.

+};
+
 TraceLogStatus::TraceLogStatus() : event_capacity(0), event_count(0) {}
 
 TraceLogStatus::~TraceLogStatus() {}
 
 // static
 TraceLog* TraceLog::GetInstance() {
   return Singleton<TraceLog, LeakySingletonTraits<TraceLog>>::get();
 }
 
 TraceLog::TraceLog()
@@ skipping 279 matching lines @@
           Bind(&TraceSamplingThread::DefaultSamplingCallback));
       sampling_thread_->RegisterSampleBucket(
           &g_trace_state[2], "bucket2",
           Bind(&TraceSamplingThread::DefaultSamplingCallback));
       if (!PlatformThread::Create(0, sampling_thread_.get(),
                                   &sampling_thread_handle_)) {
         DCHECK(false) << "failed to create thread";
       }
     }
 
+    for (auto it = thread_safe_observers_.begin();

[Primiano Tucci (use gerrit), 2016/05/09 17:18:29]

I think you can more concisely:
for (const auto& it : thread_safe_observers_)
which saves one precious line and improves readability a tiny bit

[Xiaocheng, 2016/05/10 09:33:33]

Done.

+         it != thread_safe_observers_.end(); ++it)
+      it->second.task_runner_->PostTask(
+          FROM_HERE, Bind(&ThreadSafeEnabledStateObserver::OnTraceLogEnabled,
+                          it->second.observer_));
+
     dispatching_to_observer_list_ = true;
     observer_list = enabled_state_observer_list_;
   }
   // Notify observers outside the lock in case they trigger trace events.
   for (size_t i = 0; i < observer_list.size(); ++i)
     observer_list[i]->OnTraceLogEnabled();
 
   {
     AutoLock lock(lock_);
     dispatching_to_observer_list_ = false;
@@ skipping 64 matching lines @@
 
   trace_config_.Clear();
   subtle::NoBarrier_Store(&watch_category_, 0);
   watch_event_name_ = "";
   UpdateCategoryGroupEnabledFlags();
   AddMetadataEventsWhileLocked();
 
   // Remove metadata events so they will not get added to a subsequent trace.
   metadata_events_.clear();
 
+  for (auto it = thread_safe_observers_.begin();
+       it != thread_safe_observers_.end(); ++it)
+    it->second.task_runner_->PostTask(
+        FROM_HERE, Bind(&ThreadSafeEnabledStateObserver::OnTraceLogDisabled,
+                        it->second.observer_));
+
   dispatching_to_observer_list_ = true;
   std::vector<EnabledStateObserver*> observer_list =
       enabled_state_observer_list_;
 
   {
     // Dispatch to observers outside the lock in case the observer triggers a
     // trace event.
     AutoUnlock unlock(lock_);
     for (size_t i = 0; i < observer_list.size(); ++i)
       observer_list[i]->OnTraceLogDisabled();
@@ skipping 974 matching lines @@
     }
   }
 }
 #endif  // defined(OS_WIN)
 
 void ConvertableToTraceFormat::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
   overhead->Add("ConvertableToTraceFormat(Unknown)", sizeof(*this));
 }
 
+int TraceLog::AddThreadSafeEnabledStateObserver(
+    WeakPtr<ThreadSafeEnabledStateObserver> listener) {
+  AutoLock lock(lock_);
+  int id = thread_safe_observers_.empty()

[Primiano Tucci (use gerrit), 2016/05/09 17:18:29]

Yeah I think we don't need this ID logic. Just use listener.get() as a key.

[Xiaocheng, 2016/05/10 09:33:33]

Done.

+               ? 1
+               : thread_safe_observers_.rbegin()->first + 1;
+  thread_safe_observers_.insert(
+      std::make_pair(id, RegisteredThreadSafeObserver(listener)));
+  return id;
+}
+
+void TraceLog::RemoveThreadSafeEnabledStateObserver(int listener_id) {
+  AutoLock lock(lock_);
+  thread_safe_observers_.erase(listener_id);
+}
+
+bool TraceLog::HasThreadSafeEnabledStateObserver(int listener_id) const {
+  AutoLock lock(lock_);
+  return thread_safe_observers_.find(listener_id) !=
+         thread_safe_observers_.end();
+}
+
+size_t TraceLog::GetThreadSafeObserverCountForTest() const {
+  AutoLock lock(lock_);
+  return thread_safe_observers_.size();
+}
+
 }  // namespace trace_event
 }  // namespace base
 
 namespace trace_event_internal {
 
 ScopedTraceBinaryEfficient::ScopedTraceBinaryEfficient(
     const char* category_group,
     const char* name) {
   // The single atom works because for now the category_group can only be "gpu".
   DCHECK_EQ(strcmp(category_group, "gpu"), 0);
@@ skipping 21 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_, name_,
                                                 event_handle_);
   }
 }
 
 }  // namespace trace_event_internal