Remove after wakeup logic and replace PumpTask with Fences

third_party/WebKit/Source/platform/scheduler/base/work_queue.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_WORK_QUEUE_H_
 #define THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_WORK_QUEUE_H_
 
 #include <stddef.h>
 
 #include <set>
 
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "platform/scheduler/base/enqueue_order.h"
 #include "platform/scheduler/base/task_queue_impl.h"
 
 namespace blink {
 namespace scheduler {
 namespace internal {
 class WorkQueueSets;
 
 // This class keeps track of immediate and delayed tasks which are due to run
 // now. It interfaces deeply with WorkQueueSets which keeps track of which queue
 // (with a given priority) contains the oldest task.
+//
+// If a fence is inserted, WorkQueue behaves normally up until
+// TakeTaskFromWorkQueue reaches or exceeds the fence.  At that point it the
+// API subset used by WorkQueueSets pretends the WorkQueue is empty until the
+// fence is removed.  This functionality is a primitive intended for use by
+// throttling mechanisms.
 class BLINK_PLATFORM_EXPORT WorkQueue {
  public:
   WorkQueue(TaskQueueImpl* task_queue,
             const char* name,
             TaskQueueImpl::Task::ComparatorFn queue_comparator);
   ~WorkQueue();
 
   // Associates this work queue with the given work queue sets. This must be
   // called before any tasks can be inserted into this work queue.
   void AssignToWorkQueueSets(WorkQueueSets* work_queue_sets);
 
   // Assigns the current set index.
   void AssignSetIndex(size_t work_queue_set_index);
 
   void AsValueInto(base::trace_event::TracedValue* state) const;
 
-  // Clears the |work_queue_|.
-  void Clear();
-
-  // returns true if the |work_queue_| is empty.
+  // Returns true if the |work_queue_| is empty. This method ignores any fences.
   bool Empty() const { return work_queue_.empty(); }
 
-  // If the |work_queue_| isn't empty, |enqueue_order| gets set to the enqueue
-  // order of the front task and the function returns true.  Otherwise the
-  // function returns false.
+  // If the |work_queue_| isn't empty and a fence hasn't been reached,
+  // |enqueue_order| gets set to the enqueue order of the front task and the
+  // function returns true.  Otherwise the function returns false.
   bool GetFrontTaskEnqueueOrder(EnqueueOrder* enqueue_order) const;
 
-  // Returns the first task in this queue or null if the queue is empty.
+  // Returns the first task in this queue or null if the queue is empty. This
+  // method ignores any fences.
   const TaskQueueImpl::Task* GetFrontTask() const;
 
-  // Pushes the task onto the |work_queue_| and informs the WorkQueueSets if
-  // the head changed.
+  // Returns the first task in this queue or null if the queue is empty. This
+  // method ignores any fences.
+  const TaskQueueImpl::Task* GetBackTask() const;
+
+  // Pushes the task onto the |work_queue_| and a fence hasn't been reached it
+  // informs the WorkQueueSets if the head changed.
   void Push(TaskQueueImpl::Task task);
 
   // Removes a cancelled task from the |work_queue_|. Note |key| isn't required
   // to be the original task posted, it can be a fake key constructed by
   // TaskQueueImpl::Task::CreateFakeTaskFromHandle.
   bool CancelTask(const TaskQueueImpl::Task& key);
 
   // Returns true if |work_queue_| contains a task matching |key|. Note |key|
   // isn't required to be the original task posted, it can be a fake key
   // constructed by TaskQueueImpl::Task::CreateFakeTaskFromHandle.
   bool IsTaskPending(const TaskQueueImpl::Task& key) const;
 
-  // Swap the |work_queue_| with |incoming_queue| and informs the
-  // WorkQueueSets if the head changed. Assumes |task_queue_->any_thread_lock_|
-  // is locked.
+  // Swap the |work_queue_| with |incoming_queue| and if a fence hasn't been
+  // reached it informs the WorkQueueSets if the head changed. Assumes
+  // |task_queue_->any_thread_lock_| is locked.
   void SwapLocked(TaskQueueImpl::ComparatorQueue& incoming_queue);
 
   size_t Size() const { return work_queue_.size(); }
 
-  // Pulls a task off the |work_queue_| and informs the WorkQueueSets.
+  // Pulls a task off the |work_queue_| and informs the WorkQueueSets.  If the
+  // task removed had an enqueue order >= the current fence than WorkQueue

[Sami, 2016/08/26 14:37:02]

s/than/then/

[Sami, 2016/08/26 16:44:01]

Missed this?

[alex clarke (OOO till 29th), 2016/08/26 16:47:38]

Oops done.

+  // pretends to be empty as far as the WorkQueueSets is concrned.
   TaskQueueImpl::Task TakeTaskFromWorkQueue();
 
   const char* name() const { return name_; }
 
   TaskQueueImpl* task_queue() const { return task_queue_; }
 
   WorkQueueSets* work_queue_sets() const { return work_queue_sets_; }
 
   size_t work_queue_set_index() const { return work_queue_set_index_; }
 
   // Test support function. This should not be used in production code.
   void PopTaskForTest();
 
   // Returns true if the front task in this queue has an older enqueue order
   // than the front task of |other_queue|. Both queue are assumed to be
-  // non-empty.
+  // non-empty. This method ignores any fences.
   bool ShouldRunBefore(const WorkQueue* other_queue) const;
 
+  // If |fence| is zero then WorkQueue will immediately start pretending to be
+  // empty, and returns false.

[Sami, 2016/08/26 14:37:03]

"and this function returns false"?

[alex clarke (OOO till 29th), 2016/08/26 16:33:14]

Done.

+  // If |fence| is non-zero then when TakeTaskFromWorkQueue returns a task whose
+  // enqueue_order is >= |fence| WorkQueue will start pretending to be empty.
+  // Returns true if |fence| unblocked some previously blocked tasks, returns
+  // false otherwise.
+  bool InsertFence(EnqueueOrder fence);

[Sami, 2016/08/26 14:37:03]

The API here feels slightly magical. I wonder if we should just add
set_fence_hit(bool) and have the caller either do a Remove/Insert or a
set_fence_hit(). Alternatively maybe there's a better name we could come up
with.

[alex clarke (OOO till 29th), 2016/08/26 16:33:14]

Done.

+
+  // Removes any fences that where added and if WorkQueue was pretending to be
+  // empty, then the real value is reported to WorkQueueSets. Returns true if
+  // any tasks where unblocked.
+  bool RemoveFence();
+
+  bool fence_hit() const { return fence_hit_; }
+
  private:
   TaskQueueImpl::ComparatorQueue work_queue_;
   WorkQueueSets* work_queue_sets_;  // NOT OWNED.
   TaskQueueImpl* task_queue_;       // NOT OWNED.
   size_t work_queue_set_index_;
   const char* name_;
+  EnqueueOrder fence_;
+  bool fence_hit_;
 
   DISALLOW_COPY_AND_ASSIGN(WorkQueue);
 };
 
 }  // namespace internal
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_SOURCE_PLATFORM_SCHEDULER_BASE_WORK_QUEUE_H_