1// Copyright 2013 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef MOJO_SYSTEM_WAITER_H_
6#define MOJO_SYSTEM_WAITER_H_
7
8#include "base/basictypes.h"
9#include "base/synchronization/condition_variable.h"
10#include "base/synchronization/lock.h"
11#include "mojo/public/system/core.h"
12#include "mojo/system/system_impl_export.h"
13
14namespace mojo {
15namespace system {
16
17// IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
18// under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
19// must never call out to other objects (in particular, |Dispatcher|s). This
20// class is thread-safe.
21class MOJO_SYSTEM_IMPL_EXPORT Waiter {
22 public:
23  Waiter();
24  ~Waiter();
25
26  // A |Waiter| can be used multiple times; |Init()| should be called before
27  // each time it's used.
28  void Init();
29
30  // Waits until a suitable |Awake()| is called.
31  // Returns:
32  //  - The |wake_result| passed to |Dispatcher::AddWaiter()| if it was woken up
33  //    by that dispatcher for the reason specified by |flags| (in the call to
34  //    |AddWaiter()|).
35  //  - |MOJO_RESULT_CANCELLED| if a handle (on which |MojoWait()| was called)
36  //    was closed; and
37  //  - |MOJO_RESULT_FAILED_PRECONDITION| if the reasons for being awoken given
38  //    by |flags| cannot (or can no longer) be satisfied (e.g., if the other
39  //    end of a pipe is closed).
40  MojoResult Wait(MojoDeadline deadline);
41
42  // Wake the waiter up with the given result (or no-op if it's been woken up
43  // already).
44  void Awake(MojoResult wait_result);
45
46 private:
47  base::ConditionVariable cv_;  // Associated to |lock_|.
48  base::Lock lock_;  // Protects the following members.
49#ifndef NDEBUG
50  bool initialized_;
51#endif
52  bool awoken_;
53  MojoResult wait_result_;
54
55  DISALLOW_COPY_AND_ASSIGN(Waiter);
56};
57
58}  // namespace system
59}  // namespace mojo
60
61#endif  // MOJO_SYSTEM_WAITER_H_
62