TaskScheduler [3/9] Task and Sequence

base/task_scheduler/sequence.cc

Index: base/task_scheduler/sequence.cc
diff --git a/base/task_scheduler/sequence.cc b/base/task_scheduler/sequence.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0a1202a9e6f14a5b75b0ef5ca95e8291fc23fa4c
--- /dev/null
+++ b/base/task_scheduler/sequence.cc
@@ -0,0 +1,65 @@
+// 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"
+
+namespace base {
+namespace internal {
+
+Sequence::Sequence() = default;
+
+bool Sequence::PushTask(scoped_ptr<Task> task) {
+  AutoSchedulerLock auto_lock(lock_);
+
+  ++num_tasks_per_priority_[static_cast<TaskPriorityUnderlyingType>(
+      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() {
+  AutoSchedulerLock auto_lock(lock_);
+
+  if (queue_.empty())
+    return nullptr;
+
+  return queue_.front().get();
+}
+
+bool Sequence::PopTask() {
+  AutoSchedulerLock auto_lock(lock_);
+  DCHECK(!queue_.empty());
+
+  --num_tasks_per_priority_[static_cast<TaskPriorityUnderlyingType>(
+      queue_.front()->traits.priority())];
+  queue_.pop();
+  return queue_.empty();
+}
+
+SequenceSortKey Sequence::GetSortKey() {
+  AutoSchedulerLock auto_lock(lock_);
+  DCHECK(!queue_.empty());
+
+  // Find the highest task priority in the sequence.
+  TaskPriority priority = TaskPriority::BACKGROUND;

[gab, 2016/02/18 20:22:34]

One way to avoid the signed int below would be to add TaskPriority::LOWEST. Then
since the default value here is initialized to TaskPriority::LOWEST we can loop
only until i > TaskPriority::LOWEST :-)

Also avoids having this code depend on a specific TaskPriority which is better
if we change values later.

WDYT?

[fdoray, 2016/02/18 20:52:04]

Done.

+  for (int i = kNumTaskPriorities - 1; i >= 0; --i) {

[gab, 2016/02/18 20:22:34]

Ah nice, that's actually nicer too, I used to think it was weird to use
TaskPriorityUnderlyingType as the type of kNumTaskPriorities. Using size_t for
it and int here is nicer IMO :-).

[fdoray, 2016/02/18 20:52:04]

Done.

+    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