TaskScheduler [3/9] Task and Sequence

base/task_scheduler/sequence.cc

+// Copyright 2016 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 "base/task_scheduler/sequence.h"
+
+#include <utility>
+
+#include "base/logging.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace internal {
+
+Sequence::Sequence() = default;
+
+bool Sequence::PushTask(scoped_ptr<Task> task) {
+  DCHECK(task->sequenced_time.is_null());
+  task->sequenced_time = base::TimeTicks::Now();
+
+  AutoSchedulerLock auto_lock(lock_);
+  ++num_tasks_per_priority_[static_cast<int>(task->traits.priority())];
+  queue_.push(std::move(task));
+
+  // Return true if the sequence was empty before the push.
+  return queue_.size() == 1;
+}
+
+const Task* Sequence::PeekTask() const {
+  AutoSchedulerLock auto_lock(lock_);
+
+  if (queue_.empty())
+    return nullptr;
+
+  return queue_.front().get();
+}
+
+bool Sequence::PopTask() {
+  AutoSchedulerLock auto_lock(lock_);
+  DCHECK(!queue_.empty());
+
+  const int priority_index =
+      static_cast<int>(queue_.front()->traits.priority());
+  DCHECK_GT(num_tasks_per_priority_[priority_index], 0U);
+  --num_tasks_per_priority_[priority_index];
+
+  queue_.pop();
+  return queue_.empty();
+}
+
+SequenceSortKey Sequence::GetSortKey() const {
+  TaskPriority priority = TaskPriority::LOWEST;
+  base::TimeTicks next_task_sequenced_time;
+
+  {
+    AutoSchedulerLock auto_lock(lock_);
+    DCHECK(!queue_.empty());
+
+    // Find the highest task priority in the sequence.
+    const int highest_priority_index = static_cast<int>(TaskPriority::HIGHEST);
+    const int lowest_priority_index = static_cast<int>(TaskPriority::LOWEST);
+    for (int i = highest_priority_index; i > lowest_priority_index; --i) {
+      if (num_tasks_per_priority_[i] > 0) {
+        priority = static_cast<TaskPriority>(i);
+        break;
+      }
+    }
+
+    // Save the sequenced time of the next task in the sequence.
+    next_task_sequenced_time = queue_.front()->sequenced_time;
+  }
+
+  return SequenceSortKey(priority, next_task_sequenced_time);
+}
+
+Sequence::~Sequence() = default;
+
+}  // namespace internal
+}  // namespace base