Extract Awakable from Waiter

mojo/edk/system/awakable.h

+// Copyright 2013 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.
+
+#ifndef MOJO_EDK_SYSTEM_AWAKABLE_H_
+#define MOJO_EDK_SYSTEM_AWAKABLE_H_
+
+#include <stdint.h>
+
+#include "mojo/public/c/system/types.h"
+
+namespace mojo {
+namespace system {
+
+// An interface that may be waited on |AwakableList|.
+class Awakable {
+ public:
+  // |Awake()| must satisfy the following contract:
+  // * As this is called from any thread, this must be thread-safe.
+  // * As this is called inside a lock, this must not call anything that takes
+  //   "non-terminal" locks, i.e., those which are always safe to take.
+  virtual void Awake(MojoResult result, uintptr_t context) = 0;
+
+ protected:
+  Awakable() {}
+};
+
+}  // namespace system
+}  // namespace mojo
+
+#endif  // MOJO_EDK_SYSTEM_AWAKABLE_H_