Make tasks cancellable inside the blink scheduler.

third_party/WebKit/Source/platform/scheduler/base/work_queue.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/base/work_queue.h"
 
 #include "platform/scheduler/base/work_queue_sets.h"
 
 namespace blink {
 namespace scheduler {
 namespace internal {
 
-WorkQueue::WorkQueue(TaskQueueImpl* task_queue, const char* name)
-    : work_queue_sets_(nullptr),
+WorkQueue::WorkQueue(TaskQueueImpl* task_queue,
+                     const char* name,
+                     TaskQueueImpl::Task::ComparatorFn comparator)
+    : work_queue_(comparator),
+      work_queue_sets_(nullptr),
       task_queue_(task_queue),
       work_queue_set_index_(0),
       name_(name) {}
 
 void WorkQueue::AsValueInto(base::trace_event::TracedValue* state) const {
-  // Remove const to search |work_queue_| in the destructive manner. Restore the
-  // content from |visited| later.
-  std::queue<TaskQueueImpl::Task>* mutable_queue =
-      const_cast<std::queue<TaskQueueImpl::Task>*>(&work_queue_);
-  std::queue<TaskQueueImpl::Task> visited;
-  while (!mutable_queue->empty()) {
-    TaskQueueImpl::TaskAsValueInto(mutable_queue->front(), state);
-    visited.push(std::move(mutable_queue->front()));
-    mutable_queue->pop();
+  for (const TaskQueueImpl::Task& task : work_queue_) {
+    TaskQueueImpl::TaskAsValueInto(task, state);
   }
-  *mutable_queue = std::move(visited);
 }
 
 WorkQueue::~WorkQueue() {
   DCHECK(!work_queue_sets_) << task_queue_->GetName() << " : "
                             << work_queue_sets_->name() << " : " << name_;
 }
 
 const TaskQueueImpl::Task* WorkQueue::GetFrontTask() const {
   if (work_queue_.empty())
     return nullptr;
-  return &work_queue_.front();
+  return &*work_queue_.begin();
 }
 
 bool WorkQueue::GetFrontTaskEnqueueOrder(EnqueueOrder* enqueue_order) const {
   if (work_queue_.empty())
     return false;
-  *enqueue_order = work_queue_.front().enqueue_order();
+  // Quick sanity check.
+  DCHECK_LE(work_queue_.begin()->enqueue_order(),
+            work_queue_.rbegin()->enqueue_order())
+      << task_queue_->GetName() << " : "
+      << work_queue_sets_->name() << " : " << name_;
+  *enqueue_order = work_queue_.begin()->enqueue_order();
   return true;
 }
 
 void WorkQueue::Push(TaskQueueImpl::Task task) {
   bool was_empty = work_queue_.empty();
-  work_queue_.push(std::move(task));
-  if (was_empty && work_queue_sets_)
+#ifndef NDEBUG
+  DCHECK(task.enqueue_order_set());
+#endif
+
+  // We expect |task| to be inserted at the end. Amoritized O(1).
+  work_queue_.insert(work_queue_.rbegin().base(), std::move(task));
+  DCHECK_EQ(task.enqueue_order(), work_queue_.rbegin()->enqueue_order())
+      << task_queue_->GetName() << " : "
+      << work_queue_sets_->name() << " : " << name_
+      << "task [scheduled_run_time_" << task.delayed_run_time << ", "
+      << task.sequence_num <<
+      "] rbegin() [" << work_queue_.rbegin()->delayed_run_time << ", "
+      << work_queue_.rbegin()->sequence_num << "]";
+
+  if (was_empty && work_queue_sets_) {
     work_queue_sets_->OnPushQueue(this);
+  }
 }
 
-void WorkQueue::PushAndSetEnqueueOrder(TaskQueueImpl::Task task,
-                                       EnqueueOrder enqueue_order) {
-  bool was_empty = work_queue_.empty();
-  work_queue_.push(std::move(task));
-  work_queue_.back().set_enqueue_order(enqueue_order);
+bool WorkQueue::CancelTask(const TaskQueueImpl::Task& key) {
+  TaskQueueImpl::ComparatorQueue::iterator it = work_queue_.find(key);
+  if (it == work_queue_.end())
+    return false;
 
-  if (was_empty && work_queue_sets_)
-    work_queue_sets_->OnPushQueue(this);
+  if (it == work_queue_.begin()) {
+    EnqueueOrder erased_task_enqueue_order = it->enqueue_order();
+    work_queue_.erase(it);
+    // We can't guarantee this WorkQueue is the lowest value in the WorkQueueSet
+    // so we need to use OnQueueHeadChanged instead of OnPopQueue for
+    // correctness.
+    work_queue_sets_->OnQueueHeadChanged(this, erased_task_enqueue_order);
+  } else {
+    work_queue_.erase(it);
+  }
+  task_queue_->TraceQueueSize(false);
+  return true;
+}
+
+bool WorkQueue::IsTaskPending(const TaskQueueImpl::Task& key) const {
+  return work_queue_.find(key) != work_queue_.end();
 }
 
 void WorkQueue::PopTaskForTest() {
-  work_queue_.pop();
+  if (work_queue_.empty())
+    return;
+  work_queue_.erase(work_queue_.begin());
 }
 
-void WorkQueue::SwapLocked(std::queue<TaskQueueImpl::Task>& incoming_queue) {
+void WorkQueue::SwapLocked(TaskQueueImpl::ComparatorQueue& incoming_queue) {
+  DCHECK(work_queue_.empty());
   std::swap(work_queue_, incoming_queue);
-
   if (!work_queue_.empty() && work_queue_sets_)
     work_queue_sets_->OnPushQueue(this);
   task_queue_->TraceQueueSize(true);
 }
 
 TaskQueueImpl::Task WorkQueue::TakeTaskFromWorkQueue() {
   DCHECK(work_queue_sets_);
   DCHECK(!work_queue_.empty());
-  TaskQueueImpl::Task pending_task = std::move(work_queue_.front());
-  work_queue_.pop();
+  TaskQueueImpl::ComparatorQueue::iterator it = work_queue_.begin();
+  TaskQueueImpl::Task pending_task =
+      std::move(const_cast<TaskQueueImpl::Task&>(*it));
+  work_queue_.erase(it);
   work_queue_sets_->OnPopQueue(this);
   task_queue_->TraceQueueSize(false);
   return pending_task;
 }
 
 void WorkQueue::AssignToWorkQueueSets(WorkQueueSets* work_queue_sets) {
   work_queue_sets_ = work_queue_sets;
 }
 
 void WorkQueue::AssignSetIndex(size_t work_queue_set_index) {
   work_queue_set_index_ = work_queue_set_index;
 }
 
 bool WorkQueue::ShouldRunBefore(const WorkQueue* other_queue) const {
   DCHECK(!work_queue_.empty());
   DCHECK(!other_queue->work_queue_.empty());
   EnqueueOrder enqueue_order = 0;
   EnqueueOrder other_enqueue_order = 0;
   bool have_task = GetFrontTaskEnqueueOrder(&enqueue_order);
   bool have_other_task =
       other_queue->GetFrontTaskEnqueueOrder(&other_enqueue_order);
   DCHECK(have_task);
   DCHECK(have_other_task);
   return enqueue_order < other_enqueue_order;
 }
 
 }  // namespace internal
 }  // namespace scheduler
 }  // namespace blink