Introduce a FlatMap and FlatSet into WTF

third_party/WebKit/Source/platform/scheduler/base/time_domain.h

 // 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.
 
 #ifndef THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TIME_DOMAIN_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TIME_DOMAIN_H_
 
 #include <map>
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "platform/scheduler/base/lazy_now.h"
 #include "platform/scheduler/base/task_queue_impl.h"
+#include "wtf/FlatSet.h"
 
 namespace blink {
 namespace scheduler {
 namespace internal {
 class TaskQueueImpl;
 }  // internal
 class TaskQueueManager;
 class TaskQueueManagerDelegate;
 
+std::ostream& operator<<(
+    std::ostream& os,
+    const std::pair<base::TimeTicks, internal::TaskQueueImpl*>& pair);
+
 // The TimeDomain's job is to wake task queues up when their next delayed tasks
 // are due to fire. TaskQueues request a wake up via ScheduleDelayedWork, when
 // the wake up is due the TimeDomain calls TaskQueue::WakeUpForDelayedWork.
 // The TimeDomain communicates with the TaskQueueManager to actually schedule
 // the wake-ups on the underlying base::MessageLoop. Various levels of de-duping
 // are employed to prevent unnecessary posting of TaskQueueManager::DoWork.
 //
 // Note the TimeDomain only knows about the first wakeup per queue, it's the
 // responsibility of TaskQueueImpl to keep the time domain up to date if this
 // changes.
@@ skipping 90 matching lines @@
   virtual void AsValueIntoInternal(
       base::trace_event::TracedValue* state) const = 0;
 
   // Call TaskQueueImpl::UpdateDelayedWorkQueue for each queue where the delay
   // has elapsed.
   void WakeupReadyDelayedQueues(LazyNow* lazy_now);
 
  private:
   void MoveNewlyUpdatableQueuesIntoUpdatableQueueSet();
 
-  using DelayedWakeupMultimap =
-      std::multimap<base::TimeTicks, internal::TaskQueueImpl*>;
+  using DelayedWakeupSet =
+      WTF::FlatSet<std::pair<base::TimeTicks, internal::TaskQueueImpl*>>;
 
-  DelayedWakeupMultimap delayed_wakeup_multimap_;
-
-  // This map makes it easy to remove a queue from |delayed_wakeup_multimap_|.
-  // NOTE inserting or removing elements from a std::map does not invalidate any
-  // iterators.
-  using QueueToDelayedWakeupMultimapIteratorMap =
-      std::unordered_map<internal::TaskQueueImpl*,
-                         DelayedWakeupMultimap::iterator>;
-
-  QueueToDelayedWakeupMultimapIteratorMap
-      queue_to_delayed_wakeup_multimap_iterator_map_;
+  DelayedWakeupSet delayed_wakeup_set_;
 
   // This lock guards only |newly_updatable_|.  It's not expected to be heavily
   // contended.
   base::Lock newly_updatable_lock_;
   std::vector<internal::TaskQueueImpl*> newly_updatable_;
 
   // Set of task queues with avaliable work on the incoming queue.  This should
   // only be accessed from the main thread.
   std::set<internal::TaskQueueImpl*> updatable_queue_set_;
 
+  std::set<internal::TaskQueueImpl*> queues_;
+
   Observer* observer_;  // NOT OWNED.
 
   base::ThreadChecker main_thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(TimeDomain);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_TIME_DOMAIN_H_