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
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
// SPDX-FileCopyrightText: 2022 Linus Jahn <lnj@kaidan.im>
// SPDX-FileCopyrightText: 2022 Jonah Brüchert <jbb@kaidan.im>
//
// SPDX-License-Identifier: LGPL-2.1-or-later
#ifndef QXMPPTASK_H
#define QXMPPTASK_H
#include "qxmpp_export.h"
#include <functional>
#include <memory>
#include <optional>
#include <QFuture>
#include <QPointer>
template<typename T>
class QXmppPromise;
namespace QXmpp::Private {
struct TaskData;
class QXMPP_EXPORT TaskPrivate
{
public:
TaskPrivate(void (*freeResult)(void *));
~TaskPrivate();
bool isFinished() const;
void setFinished(bool);
bool isContextAlive();
void setContext(QObject *);
void *result() const;
void setResult(void *);
void resetResult() { setResult(nullptr); }
const std::function<void(TaskPrivate &, void *)> continuation() const;
void setContinuation(std::function<void(TaskPrivate &, void *)> &&);
void invokeContinuation(void *result);
private:
std::shared_ptr<TaskData> d;
};
} // namespace QXmpp::Private
///
/// Handle for an ongoing operation that finishes in the future.
///
/// Tasks are generated by QXmppPromise and can be handled using QXmppTask::then().
///
/// Unlike QFuture, this is not thread-safe. This avoids the need to do mutex locking at every
/// access though.
///
/// \ingroup Core classes
///
/// \since QXmpp 1.5
///
template<typename T>
class QXmppTask
{
public:
~QXmppTask() = default;
///
/// Registers a function that will be called with the result as parameter when the asynchronous
/// operation finishes.
///
/// If the task is already finished when calling this (and still has a result), the function
/// will be called immediately.
///
/// If another function was previously registered using .then(), the old function will be
/// replaced, and only the new one will be called.
///
/// Example usage:
/// ```
/// QXmppTask<QString> generateSomething();
///
/// void Manager::generate()
/// {
/// generateSomething().then(this, [](QString &&result) {
/// // runs as soon as the result is finished
/// qDebug() << "Generating finished:" << result;
/// });
///
/// // The generation could still be in progress here and the lambda might not
/// // have been executed yet.
/// }
///
/// // Manager is derived from QObject.
/// ```
///
/// \param context QObject used for unregistering the handler function when the object is
/// deleted. This way your lambda will never be executed after your object has been deleted.
/// \param continuation A function accepting a result in the form of `T &&`.
///
#ifndef QXMPP_DOC
template<typename Continuation>
#endif
void then(QObject *context, Continuation continuation)
{
if constexpr (!std::is_void_v<T>) {
static_assert(std::is_invocable_v<Continuation, T &&>, "Function needs to be invocable with T &&.");
} else {
static_assert(std::is_invocable_v<Continuation>, "Function needs to be invocable without arguments.");
}
using namespace QXmpp::Private;
if (d.isFinished()) {
if constexpr (std::is_void_v<T>) {
continuation();
} else {
// when calling then() after finished value could be empty
if (hasResult()) {
continuation(std::move(*reinterpret_cast<T *>(d.result())));
d.resetResult();
}
}
} else {
d.setContext(context);
d.setContinuation([f = std::forward<Continuation>(continuation)](TaskPrivate &d, void *result) mutable {
if (d.isContextAlive()) {
if constexpr (std::is_void_v<T>) {
f();
} else {
f(std::move(*reinterpret_cast<T *>(result)));
}
}
// clear continuation to avoid "deadlocks" in case the user captured this QXmppTask
d.setContinuation({});
});
}
}
///
/// Whether the asynchronous operation is already finished.
///
/// This does not mean that the result is still stored, it might have been taken using
/// takeResult() or handled using then().
///
[[nodiscard]] bool isFinished() const { return d.isFinished(); }
///
/// Returns whether the task is finished and the value has not been taken yet.
///
#ifndef QXMPP_DOC
template<typename U = T, std::enable_if_t<(!std::is_void_v<U>)> * = nullptr>
#endif
[[nodiscard]] bool hasResult() const
{
return d.result() != nullptr;
}
///
/// The result of the operation.
///
/// \warning This can only be used once the operation is finished.
///
#ifdef QXMPP_DOC
[[nodiscard]] const T &result() const
#else
template<typename U = T, std::enable_if_t<(!std::is_void_v<U>)> * = nullptr>
[[nodiscard]] const U &result() const
#endif
{
Q_ASSERT(isFinished());
Q_ASSERT(hasResult());
return *reinterpret_cast<U *>(d.result());
}
///
/// Moves the result of the operation out of the task.
///
/// \warning This can only be used once and only after the operation has finished.
///
#ifdef QXMPP_DOC
[[nodiscard]] T takeResult()
#else
template<typename U = T, std::enable_if_t<(!std::is_void_v<U>)> * = nullptr>
[[nodiscard]] U takeResult()
#endif
{
Q_ASSERT(isFinished());
Q_ASSERT(hasResult());
U result = std::move(*reinterpret_cast<U *>(d.result()));
d.resetResult();
return result;
}
///
/// Converts the Task into a QFuture. Afterwards the QXmppTask object is invalid.
///
QFuture<T> toFuture(QObject *context)
{
QFutureInterface<T> interface;
if constexpr (std::is_same_v<T, void>) {
then(context, [interface]() mutable {
interface.reportFinished();
});
} else {
then(context, [interface](T &&val) mutable {
interface.reportResult(val);
interface.reportFinished();
});
}
return interface.future();
}
private:
friend class QXmppPromise<T>;
explicit QXmppTask(QXmpp::Private::TaskPrivate data)
: d(std::move(data))
{
}
QXmpp::Private::TaskPrivate d;
};
#endif // QXMPPTASK_H
|
