Introduce a FlatMap and FlatSet into WTF

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

Index: third_party/WebKit/Source/platform/scheduler/base/time_domain.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/base/time_domain.cc b/third_party/WebKit/Source/platform/scheduler/base/time_domain.cc
index e84c5c6f46ebbcf6c254ef35aaabc478ed4c0016..cf58f57815ddef18da54a0fb57fe589dac274eb3 100644
--- a/third_party/WebKit/Source/platform/scheduler/base/time_domain.cc
+++ b/third_party/WebKit/Source/platform/scheduler/base/time_domain.cc
@@ -13,6 +13,13 @@
 namespace blink {
 namespace scheduler {
 
+std::ostream& operator<<(
+    std::ostream& os,
+    const std::pair<base::TimeTicks, internal::TaskQueueImpl*>& pair) {
+  os << "[" << pair.first << ", " << pair.second << "]";
+  return os;
+}
+
 TimeDomain::TimeDomain(Observer* observer) : observer_(observer) {}
 
 TimeDomain::~TimeDomain() {
@@ -22,6 +29,8 @@ TimeDomain::~TimeDomain() {
 void TimeDomain::RegisterQueue(internal::TaskQueueImpl* queue) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK_EQ(queue->GetTimeDomain(), this);
+
+  queues_.insert(queue);
 }
 
 void TimeDomain::UnregisterQueue(internal::TaskQueueImpl* queue) {
@@ -29,17 +38,15 @@ void TimeDomain::UnregisterQueue(internal::TaskQueueImpl* queue) {
   DCHECK_EQ(queue->GetTimeDomain(), this);
   UnregisterAsUpdatableTaskQueue(queue);
 
-  // If present remove |task_queue| from delayed_wakeup_multimap_.
-  // O(log n)
-  QueueToDelayedWakeupMultimapIteratorMap::iterator it =
-      queue_to_delayed_wakeup_multimap_iterator_map_.find(queue);
-
-  if (it == queue_to_delayed_wakeup_multimap_iterator_map_.end())
+  // If no wakeup has been requested then bail out.
+  if (queue->time_domain_wakeup().is_null())
     return;
 
-  // O(1) amortized.
-  delayed_wakeup_multimap_.erase(it->second);
-  queue_to_delayed_wakeup_multimap_iterator_map_.erase(it);
+  // O(log n + n / 2)
+  delayed_wakeup_set_.erase(std::make_pair(queue->time_domain_wakeup(), queue));
+  queue->set_time_domain_wakeup(base::TimeTicks());
+
+  queues_.erase(queue);
 }
 
 void TimeDomain::MigrateQueue(internal::TaskQueueImpl* queue,
@@ -53,21 +60,17 @@ void TimeDomain::MigrateQueue(internal::TaskQueueImpl* queue,
   if (UnregisterAsUpdatableTaskQueue(queue))
     destination_time_domain->updatable_queue_set_.insert(queue);
 
-  // If present remove |task_queue| from delayed_wakeup_multimap_.
-  // O(log n)
-  QueueToDelayedWakeupMultimapIteratorMap::iterator it =
-      queue_to_delayed_wakeup_multimap_iterator_map_.find(queue);
-
-  if (it == queue_to_delayed_wakeup_multimap_iterator_map_.end())
+  // If no wakeup has been requested then bail out.
+  if (queue->time_domain_wakeup().is_null())
     return;
 
-  base::TimeTicks destination_now = destination_time_domain->Now();
-  destination_time_domain->ScheduleDelayedWork(queue, it->second->first,
-                                               destination_now);
+  // O(log n + n / 2)
+  delayed_wakeup_set_.erase(std::make_pair(queue->time_domain_wakeup(), queue));
+  queue->set_time_domain_wakeup(base::TimeTicks());
 
-  // O(1) amortized.
-  delayed_wakeup_multimap_.erase(it->second);
-  queue_to_delayed_wakeup_multimap_iterator_map_.erase(it);
+  base::TimeTicks destination_now = destination_time_domain->Now();
+  destination_time_domain->ScheduleDelayedWork(
+      queue, queue->time_domain_wakeup(), destination_now);
 }
 
 void TimeDomain::ScheduleDelayedWork(internal::TaskQueueImpl* queue,
@@ -76,27 +79,20 @@ void TimeDomain::ScheduleDelayedWork(internal::TaskQueueImpl* queue,
   DCHECK(main_thread_checker_.CalledOnValidThread());
   // We only want to store a single wakeup per queue, so we need to remove any
   // previously registered wake up for |queue|.
-  QueueToDelayedWakeupMultimapIteratorMap::iterator it =
-      queue_to_delayed_wakeup_multimap_iterator_map_.find(queue);
-
-  if (it != queue_to_delayed_wakeup_multimap_iterator_map_.end())
-    delayed_wakeup_multimap_.erase(it->second);
+  if (!queue->time_domain_wakeup().is_null()) {
+    delayed_wakeup_set_.erase(
+        std::make_pair(queue->time_domain_wakeup(), queue));
+    queue->set_time_domain_wakeup(base::TimeTicks());
+  }
 
-  if (delayed_wakeup_multimap_.empty() ||
-      delayed_run_time < delayed_wakeup_multimap_.begin()->first) {
+  if (delayed_wakeup_set_.empty() ||
+      delayed_run_time < delayed_wakeup_set_.begin()->first) {
     base::TimeDelta delay = std::max(base::TimeDelta(), delayed_run_time - now);
     RequestWakeup(now, delay);
   }
 
-  if (it != queue_to_delayed_wakeup_multimap_iterator_map_.end()) {
-    // TODO(alexclarke): Use C++17 extract & insert to more efficiently modify
-    // |queue_to_delayed_wakeup_multimap_iterator_map_|.
-    it->second = delayed_wakeup_multimap_.insert({delayed_run_time, queue});
-  } else {
-    // Insert the wakeup and store the map iterator for later convenience.
-    queue_to_delayed_wakeup_multimap_iterator_map_.insert(
-        {queue, delayed_wakeup_multimap_.insert({delayed_run_time, queue})});
-  }
+  delayed_wakeup_set_.insert(std::make_pair(delayed_run_time, queue));
+  queue->set_time_domain_wakeup(delayed_run_time);
 
   if (observer_)
     observer_->OnTimeDomainHasDelayedWork(queue);
@@ -167,38 +163,31 @@ void TimeDomain::WakeupReadyDelayedQueues(LazyNow* lazy_now) {
   // Wake up any queues with pending delayed work.  Note std::multipmap stores
   // the elements sorted by key, so the begin() iterator points to the earliest
   // queue to wakeup.
-  while (!delayed_wakeup_multimap_.empty()) {
-    DelayedWakeupMultimap::iterator next_wakeup =
-        delayed_wakeup_multimap_.begin();
-    if (next_wakeup->first > lazy_now->Now())
-      break;
-
-    internal::TaskQueueImpl* queue = next_wakeup->second;
-
-    // O(1) amortized.
-    delayed_wakeup_multimap_.erase(next_wakeup);
-    // O(log n).
-    queue_to_delayed_wakeup_multimap_iterator_map_.erase(queue);
+  while (!delayed_wakeup_set_.empty() &&
+         delayed_wakeup_set_.begin()->first <= lazy_now->Now()) {
+    internal::TaskQueueImpl* queue = delayed_wakeup_set_.begin()->second;
+    delayed_wakeup_set_.erase(delayed_wakeup_set_.begin());
 
+    queue->set_time_domain_wakeup(base::TimeTicks());
     queue->WakeUpForDelayedWork(lazy_now);
   }
 }
 
 bool TimeDomain::NextScheduledRunTime(base::TimeTicks* out_time) const {
   DCHECK(main_thread_checker_.CalledOnValidThread());
-  if (delayed_wakeup_multimap_.empty())
+  if (delayed_wakeup_set_.empty())
     return false;
 
-  *out_time = delayed_wakeup_multimap_.begin()->first;
+  *out_time = delayed_wakeup_set_.begin()->first;
   return true;
 }
 
 bool TimeDomain::NextScheduledTaskQueue(TaskQueue** out_task_queue) const {
   DCHECK(main_thread_checker_.CalledOnValidThread());
-  if (delayed_wakeup_multimap_.empty())
+  if (delayed_wakeup_set_.empty())
     return false;
 
-  *out_task_queue = delayed_wakeup_multimap_.begin()->second;
+  *out_task_queue = delayed_wakeup_set_.begin()->second;
   return true;
 }
 
@@ -209,9 +198,9 @@ void TimeDomain::AsValueInto(base::trace_event::TracedValue* state) const {
   for (auto* queue : updatable_queue_set_)
     state->AppendString(queue->GetName());
   state->EndArray();
-  state->SetInteger("registered_delay_count", delayed_wakeup_multimap_.size());
-  if (!delayed_wakeup_multimap_.empty()) {
-    base::TimeDelta delay = delayed_wakeup_multimap_.begin()->first - Now();
+  state->SetInteger("registered_delay_count", delayed_wakeup_set_.size());
+  if (!delayed_wakeup_set_.empty()) {
+    base::TimeDelta delay = delayed_wakeup_set_.begin()->first - Now();
     state->SetDouble("next_delay_ms", delay.InMillisecondsF());
   }
   AsValueIntoInternal(state);