1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
|
// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef dap_future_h
#define dap_future_h
#include <condition_variable>
#include <memory>
#include <mutex>
namespace dap {
// internal functionality
namespace detail {
template <typename T>
struct promise_state {
T val;
std::mutex mutex;
std::condition_variable cv;
bool hasVal = false;
};
} // namespace detail
// forward declaration
template <typename T>
class promise;
// future_status is the enumeration returned by future::wait_for and
// future::wait_until.
enum class future_status {
ready,
timeout,
};
// future is a minimal reimplementation of std::future, that does not suffer
// from TSAN false positives. See:
// https://gcc.gnu.org/bugzilla//show_bug.cgi?id=69204
template <typename T>
class future {
public:
using State = detail::promise_state<T>;
// constructors
inline future() = default;
inline future(future&&) = default;
// valid() returns true if the future has an internal state.
bool valid() const;
// get() blocks until the future has a valid result, and returns it.
// The future must have a valid internal state to call this method.
inline T get();
// wait() blocks until the future has a valid result.
// The future must have a valid internal state to call this method.
void wait() const;
// wait_for() blocks until the future has a valid result, or the timeout is
// reached.
// The future must have a valid internal state to call this method.
template <class Rep, class Period>
future_status wait_for(
const std::chrono::duration<Rep, Period>& timeout) const;
// wait_until() blocks until the future has a valid result, or the timeout is
// reached.
// The future must have a valid internal state to call this method.
template <class Clock, class Duration>
future_status wait_until(
const std::chrono::time_point<Clock, Duration>& timeout) const;
private:
friend promise<T>;
future(const future&) = delete;
inline future(const std::shared_ptr<State>& state);
std::shared_ptr<State> state = std::make_shared<State>();
};
template <typename T>
future<T>::future(const std::shared_ptr<State>& s) : state(s) {}
template <typename T>
bool future<T>::valid() const {
return static_cast<bool>(state);
}
template <typename T>
T future<T>::get() {
std::unique_lock<std::mutex> lock(state->mutex);
state->cv.wait(lock, [&] { return state->hasVal; });
return state->val;
}
template <typename T>
void future<T>::wait() const {
std::unique_lock<std::mutex> lock(state->mutex);
state->cv.wait(lock, [&] { return state->hasVal; });
}
template <typename T>
template <class Rep, class Period>
future_status future<T>::wait_for(
const std::chrono::duration<Rep, Period>& timeout) const {
std::unique_lock<std::mutex> lock(state->mutex);
return state->cv.wait_for(lock, timeout, [&] { return state->hasVal; })
? future_status::ready
: future_status::timeout;
}
template <typename T>
template <class Clock, class Duration>
future_status future<T>::wait_until(
const std::chrono::time_point<Clock, Duration>& timeout) const {
std::unique_lock<std::mutex> lock(state->mutex);
return state->cv.wait_until(lock, timeout, [&] { return state->hasVal; })
? future_status::ready
: future_status::timeout;
}
// promise is a minimal reimplementation of std::promise, that does not suffer
// from TSAN false positives. See:
// https://gcc.gnu.org/bugzilla//show_bug.cgi?id=69204
template <typename T>
class promise {
public:
// constructors
inline promise() = default;
inline promise(promise&& other) = default;
inline promise(const promise& other) = default;
// set_value() stores value to the shared state.
// set_value() must only be called once.
inline void set_value(const T& value) const;
inline void set_value(T&& value) const;
// get_future() returns a future sharing this promise's state.
future<T> get_future();
private:
using State = detail::promise_state<T>;
std::shared_ptr<State> state = std::make_shared<State>();
};
template <typename T>
future<T> promise<T>::get_future() {
return future<T>(state);
}
template <typename T>
void promise<T>::set_value(const T& value) const {
std::unique_lock<std::mutex> lock(state->mutex);
state->val = value;
state->hasVal = true;
state->cv.notify_all();
}
template <typename T>
void promise<T>::set_value(T&& value) const {
std::unique_lock<std::mutex> lock(state->mutex);
state->val = std::move(value);
state->hasVal = true;
state->cv.notify_all();
}
} // namespace dap
#endif // dap_future_h
|
