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_);
+
+  const TaskPriorityUnderlyingType priority_index =
+      static_cast<TaskPriorityUnderlyingType>(task->traits.priority());
+  ++num_tasks_per_priority_[priority_index];
+
+  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 TaskPriorityUnderlyingType priority_index =
+      static_cast<TaskPriorityUnderlyingType>(
+          queue_.front()->traits.priority());
+  --num_tasks_per_priority_[priority_index];
+
+  queue_.pop();
+  return queue_.empty();
+}
+
+SequenceSortKey Sequence::GetSortKey() const {
+  AutoSchedulerLock auto_lock(lock_);
+  DCHECK(!queue_.empty());
+
+  // Find the highest task priority in the sequence.

[robliao, 2016/02/22 21:34:12]

We should add a static_assert here
static_assert(TaskPriority::HIGHEST == kNumTaskPriorities - 1)

[gab, 2016/02/22 21:40:24]

There was one, but removed per my request. Ref:
https://codereview.chromium.org/1705253002/diff/160001/base/task_scheduler/se...

[robliao, 2016/02/22 21:45:48]

Ah, missed that. The reason why a static_assert would be appropriate is that
SequenceSortKey takes advantage of an implementation detail of how TaskPriority
is defined. This file depends on that definition, and so a static_assert would
be helpful in pointing that out.

[fdoray, 2016/02/23 13:38:36]

Done. static_assert is back as we discussed yesterday.

+  TaskPriority priority = TaskPriority::LOWEST;
+  for (TaskPriorityUnderlyingType i =
+           static_cast<TaskPriorityUnderlyingType>(TaskPriority::HIGHEST);
+       i > static_cast<TaskPriorityUnderlyingType>(TaskPriority::LOWEST); --i) {
+    if (num_tasks_per_priority_[i] > 0) {
+      priority = static_cast<TaskPriority>(i);
+      break;
+    }
+  }
+
+  return SequenceSortKey(priority, queue_.front()->sequenced_time);
+}
+
+Sequence::~Sequence() = default;
+
+}  // namespace internal
+}  // namespace base