Remove after wakeup logic and replace PumpTask with Fences

third_party/WebKit/Source/platform/scheduler/renderer/throttling_helper.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 "platform/scheduler/renderer/throttling_helper.h"
 
 #include "base/logging.h"
 #include "platform/scheduler/base/real_time_domain.h"
 #include "platform/scheduler/child/scheduler_tqm_delegate.h"
 #include "platform/scheduler/renderer/auto_advancing_virtual_time_domain.h"
 #include "platform/scheduler/renderer/renderer_scheduler_impl.h"
 #include "platform/scheduler/renderer/throttled_time_domain.h"
 #include "platform/scheduler/renderer/web_frame_scheduler_impl.h"
 #include "public/platform/WebFrameScheduler.h"
 
 namespace blink {
 namespace scheduler {
 
 ThrottlingHelper::ThrottlingHelper(RendererSchedulerImpl* renderer_scheduler,
                                    const char* tracing_category)
     : task_runner_(renderer_scheduler->ControlTaskRunner()),
       renderer_scheduler_(renderer_scheduler),
       tick_clock_(renderer_scheduler->tick_clock()),
       tracing_category_(tracing_category),
       time_domain_(new ThrottledTimeDomain(this, tracing_category)),
       virtual_time_(false),
+      ignore_incoming_immediate_work_(false),
       weak_factory_(this) {
   pump_throttled_tasks_closure_.Reset(base::Bind(
       &ThrottlingHelper::PumpThrottledTasks, weak_factory_.GetWeakPtr()));
   forward_immediate_work_closure_ =
       base::Bind(&ThrottlingHelper::OnTimeDomainHasImmediateWork,
                  weak_factory_.GetWeakPtr());
 
   renderer_scheduler_->RegisterTimeDomain(time_domain_.get());
 }
 
 ThrottlingHelper::~ThrottlingHelper() {
   // It's possible for queues to be still throttled, so we need to tidy up
   // before unregistering the time domain.
   for (const TaskQueueMap::value_type& map_entry : throttled_queues_) {
     TaskQueue* task_queue = map_entry.first;
     task_queue->SetTimeDomain(renderer_scheduler_->real_time_domain());
-    task_queue->SetPumpPolicy(TaskQueue::PumpPolicy::AUTO);
   }
 
   renderer_scheduler_->UnregisterTimeDomain(time_domain_.get());
 }
 
 void ThrottlingHelper::SetQueueEnabled(TaskQueue* task_queue, bool enabled) {
   TaskQueueMap::iterator find_it = throttled_queues_.find(task_queue);
 
   if (find_it == throttled_queues_.end()) {
     task_queue->SetQueueEnabled(enabled);
@@ skipping 15 matching lines @@
   if (virtual_time_)
     return;
 
   std::pair<TaskQueueMap::iterator, bool> insert_result =
       throttled_queues_.insert(std::make_pair(
           task_queue, Metadata(1, task_queue->IsQueueEnabled())));
 
   if (insert_result.second) {
     // The insert was succesful so we need to throttle the queue.
     task_queue->SetTimeDomain(time_domain_.get());
-    task_queue->SetPumpPolicy(TaskQueue::PumpPolicy::MANUAL);
     task_queue->SetQueueEnabled(false);
 
     if (!task_queue->IsEmpty()) {
       if (task_queue->HasPendingImmediateWork()) {
         OnTimeDomainHasImmediateWork();
       } else {
         OnTimeDomainHasDelayedWork();
       }
     }
   } else {
     // An entry already existed in the map so we need to increment the refcount.
     insert_result.first->second.throttling_ref_count++;
   }
 }
 
 void ThrottlingHelper::DecreaseThrottleRefCount(TaskQueue* task_queue) {
   if (virtual_time_)
     return;
 
   TaskQueueMap::iterator iter = throttled_queues_.find(task_queue);
 
   if (iter != throttled_queues_.end() &&
       --iter->second.throttling_ref_count == 0) {
     bool enabled = iter->second.enabled;
     // The refcount has become zero, we need to unthrottle the queue.
     throttled_queues_.erase(iter);
 
     task_queue->SetTimeDomain(renderer_scheduler_->real_time_domain());
-    task_queue->SetPumpPolicy(TaskQueue::PumpPolicy::AUTO);
     task_queue->SetQueueEnabled(enabled);
   }
 }
 
+bool ThrottlingHelper::IsThrottled(TaskQueue* task_queue) const {
+  return throttled_queues_.find(task_queue) != throttled_queues_.end();
+}
+
 void ThrottlingHelper::UnregisterTaskQueue(TaskQueue* task_queue) {
   throttled_queues_.erase(task_queue);
 }
 
 void ThrottlingHelper::OnTimeDomainHasImmediateWork() {
   // Forward to the main thread if called from another thread.
   if (!task_runner_->RunsTasksOnCurrentThread()) {
     task_runner_->PostTask(FROM_HERE, forward_immediate_work_closure_);
     return;
   }
+  // Posting ThrottlingHelper::MaybeDisableQueue doesn't count!

[Sami, 2016/08/25 15:54:13]

Isn't OnTimeDomainHasImmediateWork is only called when an empty queue becomes
non-empty? Since we only post MaybeDisableQueue on non-empty queues, this
shouldn't get called -- or did I miss something?

[alex clarke (OOO till 29th), 2016/08/26 13:29:09]

This has gone away.

+  if (ignore_incoming_immediate_work_)
+    return;
   TRACE_EVENT0(tracing_category_,
                "ThrottlingHelper::OnTimeDomainHasImmediateWork");
   base::TimeTicks now = tick_clock_->NowTicks();
   MaybeSchedulePumpThrottledTasksLocked(FROM_HERE, now, now);
 }
 
 void ThrottlingHelper::OnTimeDomainHasDelayedWork() {
   TRACE_EVENT0(tracing_category_,
                "ThrottlingHelper::OnTimeDomainHasDelayedWork");
   base::TimeTicks next_scheduled_delayed_task;
   bool has_delayed_task =
       time_domain_->NextScheduledRunTime(&next_scheduled_delayed_task);
   DCHECK(has_delayed_task);
   base::TimeTicks now = tick_clock_->NowTicks();
   MaybeSchedulePumpThrottledTasksLocked(FROM_HERE, now,
                                         next_scheduled_delayed_task);
 }
 
 void ThrottlingHelper::PumpThrottledTasks() {
   TRACE_EVENT0(tracing_category_, "ThrottlingHelper::PumpThrottledTasks");
   pending_pump_throttled_tasks_runtime_ = base::TimeTicks();
 
   LazyNow lazy_low(tick_clock_);
+  // Make sure posting MaybeDisableQueue doesn't trigger another pump.
+  ignore_incoming_immediate_work_ = true;

[Sami, 2016/08/25 15:54:13]

nit: base::AutoReset?

[alex clarke (OOO till 29th), 2016/08/26 13:29:08]

This has gone away.

   for (const TaskQueueMap::value_type& map_entry : throttled_queues_) {
     TaskQueue* task_queue = map_entry.first;
-    if (task_queue->IsEmpty())
+    if (task_queue->IsEmpty() || !map_entry.second.enabled) {

[Sami, 2016/08/25 15:54:13]

nit: might want to short-circuit .enabled first since IsEmpty() potentially
takes a lock.

[alex clarke (OOO till 29th), 2016/08/26 13:29:09]

Done.

       continue;
+    }
 
-    task_queue->SetQueueEnabled(map_entry.second.enabled);
-    task_queue->PumpQueue(&lazy_low, false);
+    // Post a task to disable |task_queue|, which ensures that no tasks posted
+    // after this point will be run until next time.
+    task_queue->PostTask(FROM_HERE,

[Sami, 2016/08/25 15:54:13]

Could IsEmpty() above get fooled by this task that we're posting here, causing
us to post another disable task here? For example if we had two throttled task
queues A and B and A is starving B, then B will incrementally get more of these
tasks posted on it.

(Maybe IsEmpty() isn't the issue but rather our knowledge of whether there are
tasks other than MaybeDisableQueue in the queue.)

[alex clarke (OOO till 29th), 2016/08/26 13:29:09]

This has gone away.

+                         base::Bind(&ThrottlingHelper::MaybeDisableQueue,
+                                    weak_factory_.GetWeakPtr(), task_queue));
+    task_queue->SetQueueEnabled(true);
   }
+  ignore_incoming_immediate_work_ = false;
+
   // Make sure NextScheduledRunTime gives us an up-to date result.
   time_domain_->ClearExpiredWakeups();
 
   base::TimeTicks next_scheduled_delayed_task;
   // Maybe schedule a call to ThrottlingHelper::PumpThrottledTasks if there is
   // a pending delayed task. NOTE posting a non-delayed task in the future will
   // result in ThrottlingHelper::OnTimeDomainHasImmediateWork being called.
   if (time_domain_->NextScheduledRunTime(&next_scheduled_delayed_task)) {
     MaybeSchedulePumpThrottledTasksLocked(FROM_HERE, lazy_low.Now(),
                                           next_scheduled_delayed_task);
   }
 }
 
+void ThrottlingHelper::MaybeDisableQueue(TaskQueue* task_queue) {
+  // It's quite possible the queue is no longer throttled in which case we
+  // should bail out.
+  if (throttled_queues_.find(task_queue) == throttled_queues_.end())

[Sami, 2016/08/25 15:54:13]

nit: Could call IsThrottled()

[alex clarke (OOO till 29th), 2016/08/26 13:29:09]

This has gone away.

+    return;
+
+  task_queue->SetQueueEnabled(false);
+
+  // Normally ThrottlingHelper::OnTimeDomainHasImmediateWork would detect
+  // extra work, but that call only happens if the queue was empty. So
+  // We need an extra check here to determine if there's more work to do.
+  if (task_queue->HasPendingImmediateWork()) {
+    base::TimeTicks now = tick_clock_->NowTicks();
+    MaybeSchedulePumpThrottledTasksLocked(FROM_HERE, now, now);
+  }
+}
+
 /* static */
 base::TimeTicks ThrottlingHelper::ThrottledRunTime(
     base::TimeTicks unthrottled_runtime) {
   const base::TimeDelta one_second = base::TimeDelta::FromSeconds(1);
   return unthrottled_runtime + one_second -
          ((unthrottled_runtime - base::TimeTicks()) % one_second);
 }
 
 void ThrottlingHelper::MaybeSchedulePumpThrottledTasksLocked(
     const tracked_objects::Location& from_here,
@@ skipping 28 matching lines @@
 
   pump_throttled_tasks_closure_.Cancel();
 
   while (!throttled_queues_.empty()) {
     TaskQueue* task_queue = throttled_queues_.begin()->first;
     bool enabled = throttled_queues_.begin()->second.enabled;
 
     throttled_queues_.erase(throttled_queues_.begin());
 
     task_queue->SetTimeDomain(renderer_scheduler_->GetVirtualTimeDomain());
-    task_queue->SetPumpPolicy(TaskQueue::PumpPolicy::AUTO);
     task_queue->SetQueueEnabled(enabled);
   }
 }
 
 }  // namespace scheduler
 }  // namespace blink