Mojo: Move waiting APIs to public library

mojo/edk/system/waiter.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_WAITER_H_
-#define MOJO_EDK_SYSTEM_WAITER_H_
-
-#include <stdint.h>
-
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/synchronization/condition_variable.h"
-#include "base/synchronization/lock.h"
-#include "mojo/edk/system/awakable.h"
-#include "mojo/edk/system/system_impl_export.h"
-#include "mojo/public/c/system/types.h"
-
-namespace mojo {
-namespace edk {
-
-// IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
-// under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
-// must never call out to other objects (in particular, |Dispatcher|s). This
-// class is thread-safe.
-class MOJO_SYSTEM_IMPL_EXPORT Waiter final : public Awakable {
- public:
-  Waiter();
-  ~Waiter();
-
-  // A |Waiter| can be used multiple times; |Init()| should be called before
-  // each time it's used.
-  void Init();
-
-  // Waits until a suitable |Awake()| is called. (|context| may be null, in
-  // which case, obviously no context is ever returned.)
-  // Returns:
-  //   - The result given to the first call to |Awake()| (possibly before this
-  //     call to |Wait()|); in this case, |*context| is set to the value passed
-  //     to that call to |Awake()|.
-  //   - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this
-  //     case |*context| is not modified.
-  //
-  // Usually, the context passed to |Awake()| will be the value passed to
-  // |Dispatcher::AddAwakable()|, which is usually the index to the array of
-  // handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|).
-  //
-  // Typical |Awake()| results are:
-  //   - |MOJO_RESULT_OK| if one of the flags passed to
-  //     |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddAwakable()|) was
-  //     satisfied;
-  //   - |MOJO_RESULT_CANCELLED| if a handle (on which
-  //     |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the
-  //     dispatcher closed); and
-  //   - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to
-  //     |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by
-  //     the corresponding handle (e.g., if the other end of a message or data
-  //     pipe is closed).
-  MojoResult Wait(MojoDeadline deadline, uintptr_t* context);
-
-  // Wake the waiter up with the given result and context (or no-op if it's been
-  // woken up already).
-  bool Awake(MojoResult result, uintptr_t context) override;
-
- private:
-  base::Lock lock_;             // Protects the following members.
-  base::ConditionVariable cv_;  // Associated to |lock_|.
-#if DCHECK_IS_ON()
-  bool initialized_;
-#endif
-  bool awoken_;
-  MojoResult awake_result_;
-  uintptr_t awake_context_;
-
-  DISALLOW_COPY_AND_ASSIGN(Waiter);
-};
-
-}  // namespace edk
-}  // namespace mojo
-
-#endif  // MOJO_EDK_SYSTEM_WAITER_H_