TaskScheduler: Add internal::GetTaskPriorityForCurrentThread().

base/task_scheduler/task_priority_for_current_thread.cc

Index: base/task_scheduler/task_priority_for_current_thread.cc
diff --git a/base/task_scheduler/task_priority_for_current_thread.cc b/base/task_scheduler/task_priority_for_current_thread.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c63326f9d94db89a92e22d123b24924f7a99f6eb
--- /dev/null
+++ b/base/task_scheduler/task_priority_for_current_thread.cc
@@ -0,0 +1,41 @@
+// 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/task_priority_for_current_thread.h"
+
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/threading/thread_local.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+
+LazyInstance<ThreadLocalPointer<const TaskPriority>>::Leaky

[robliao, 2016/12/01 19:27:27]

Would ThreadLocalStorage::StaticSlot tls... = TLS_INITIALIZER work better here?

[fdoray, 2016/12/01 19:41:07]

I doubt it.

1. I don't need more direct control of the slot
https://cs.chromium.org/chromium/src/base/threading/thread_local_storage.h?sq...
2. I would need to initialize the slot myself
https://cs.chromium.org/chromium/src/base/threading/thread_local_storage.h?sq...
. LazyInstance+ThreadLocalPointer handles that for me.

[robliao, 2016/12/01 20:08:57]

sgtm.

+    tls_task_priority_for_current_thread = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+ScopedSetTaskPriorityForCurrentThread::ScopedSetTaskPriorityForCurrentThread(
+    TaskPriority priority)
+    : priority_(priority) {
+  DCHECK(!tls_task_priority_for_current_thread.Get().Get());
+  tls_task_priority_for_current_thread.Get().Set(&priority_);
+}
+
+ScopedSetTaskPriorityForCurrentThread::
+    ~ScopedSetTaskPriorityForCurrentThread() {
+  DCHECK_EQ(&priority_, tls_task_priority_for_current_thread.Get().Get());
+  tls_task_priority_for_current_thread.Get().Set(nullptr);
+}
+
+TaskPriority GetTaskPriorityForCurrentThread() {
+  const TaskPriority* priority =
+      tls_task_priority_for_current_thread.Get().Get();
+  return priority ? *priority : TaskPriority::USER_VISIBLE;
+}
+
+}  // namespace internal
+}  // namespace base