qfuture.h

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#ifndef QFUTURE_H
#define QFUTURE_H
 
#include <QtCore/qglobal.h>
 
#include <QtCore/qfutureinterface.h>
#include <QtCore/qmetatype.h>
#include <QtCore/qstring.h>
 
#include <QtCore/qfuture_impl.h>
 
#include <type_traits>
 
QT_REQUIRE_CONFIG(future);
 
QT_BEGIN_NAMESPACE
 
template <typename T>
class QFutureWatcher;
 
template <typename T>
class QFuture
{
    static_assert (std::is_move_constructible_v<T>
                   || std::is_same_v<T, void>,
                   "A move-constructible type or type void is required");
public:
    QFuture()
        : d(QFutureInterface<T>::canceledResult())
    { }
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    explicit QFuture(QFutureInterface<T> *p) // internal
        : d(*p)
    { }
 
    template<typename U = T, typename = QtPrivate::EnableForVoid<U>>
    explicit QFuture(QFutureInterfaceBase *p) // internal
        : d(*p)
    {
    }
 
    template<typename U, typename V = T, typename = QtPrivate::EnableForVoid<V>>
    explicit QFuture(const QFuture<U> &other) : d(other.d)
    {
    }
 
    template<typename U, typename V = T, typename = QtPrivate::EnableForVoid<V>>
    QFuture<void> &operator=(const QFuture<U> &other)
    {
        d = other.d;
        return *this;
    }
 
#if defined(Q_QDOC)
    ~QFuture() { }
    QFuture(const QFuture<T> &) { }
    QFuture<T> & operator=(const QFuture<T> &) { }
#endif
 
    void cancel() { d.cancel(); }
    bool isCanceled() const { return d.isCanceled(); }
 
#if QT_DEPRECATED_SINCE(6, 0)
    QT_DEPRECATED_VERSION_X_6_0("Use setSuspended() instead.")
    void setPaused(bool paused) { d.setSuspended(paused); }
 
    QT_DEPRECATED_VERSION_X_6_0("Use isSuspending() or isSuspended() instead.")
    bool isPaused() const
    {
QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
        return d.isPaused();
QT_WARNING_POP
    }
 
    QT_DEPRECATED_VERSION_X_6_0("Use toggleSuspended() instead.")
    void togglePaused() { d.toggleSuspended(); }
 
    QT_DEPRECATED_VERSION_X_6_0("Use suspend() instead.")
    void pause() { suspend(); }
#endif
    bool isSuspending() const { return d.isSuspending(); }
    bool isSuspended() const { return d.isSuspended(); }
    void setSuspended(bool suspend) { d.setSuspended(suspend); }
    void suspend() { setSuspended(true); }
    void resume() { setSuspended(false); }
    void toggleSuspended() { d.toggleSuspended(); }
 
    bool isStarted() const { return d.isStarted(); }
    bool isFinished() const { return d.isFinished(); }
    bool isRunning() const { return d.isRunning(); }
 
    int resultCount() const { return d.resultCount(); }
    int progressValue() const { return d.progressValue(); }
    int progressMinimum() const { return d.progressMinimum(); }
    int progressMaximum() const { return d.progressMaximum(); }
    QString progressText() const { return d.progressText(); }
    void waitForFinished() { d.waitForFinished(); }
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    inline T result() const;
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    inline T resultAt(int index) const;
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    bool isResultReadyAt(int resultIndex) const { return d.isResultReadyAt(resultIndex); }
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    QList<T> results() const { return d.results(); }
 
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    T takeResult() { return d.takeResult(); }
 
#if 0
    // TODO: Enable and make it return a QList, when QList is fixed to support move-only types
    template<typename U = T, typename = QtPrivate::EnableForNonVoid<U>>
    std::vector<T> takeResults() { return d.takeResults(); }
#endif
 
    bool isValid() const { return d.isValid(); }
 
    template<class Function>
    using ResultType = typename QtPrivate::ResultTypeHelper<Function, T>::ResultType;
 
    template<class Function>
    QFuture<ResultType<Function>> then(Function &&function);
 
    template<class Function>
    QFuture<ResultType<Function>> then(QtFuture::Launch policy, Function &&function);
 
    template<class Function>
    QFuture<ResultType<Function>> then(QThreadPool *pool, Function &&function);
 
    template<class Function>
    QFuture<ResultType<Function>> then(QObject *context, Function &&function);
 
#ifndef QT_NO_EXCEPTIONS
    template<class Function,
             typename = std::enable_if_t<!QtPrivate::ArgResolver<Function>::HasExtraArgs>>
    QFuture<T> onFailed(Function &&handler);
 
    template<class Function,
             typename = std::enable_if_t<!QtPrivate::ArgResolver<Function>::HasExtraArgs>>
    QFuture<T> onFailed(QObject *context, Function &&handler);
#endif
 
    template<class Function, typename = std::enable_if_t<std::is_invocable_r_v<T, Function>>>
    QFuture<T> onCanceled(Function &&handler);
 
    template<class Function, typename = std::enable_if_t<std::is_invocable_r_v<T, Function>>>
    QFuture<T> onCanceled(QObject *context, Function &&handler);
 
#if !defined(Q_QDOC)
    template<class U = T, typename = std::enable_if_t<QtPrivate::isQFutureV<U>>>
    auto unwrap();
#else
    template<class U>
    QFuture<U> unwrap();
#endif
 
    class const_iterator
    {
    public:
        static_assert(!std::is_same_v<T, void>,
                      "It isn't possible to define QFuture<void>::const_iterator");
 
        typedef std::bidirectional_iterator_tag iterator_category;
        typedef qptrdiff difference_type;
        typedef T value_type;
        typedef const T *pointer;
        typedef const T &reference;
 
        inline const_iterator() {}
        inline const_iterator(QFuture const * const _future, int _index)
        : future(_future), index(advanceIndex(_index, 0)) { }
        inline const_iterator(const const_iterator &o) : future(o.future), index(o.index)  {}
        inline const_iterator &operator=(const const_iterator &o)
        { future = o.future; index = o.index; return *this; }
        inline const T &operator*() const { return future->d.resultReference(index); }
        inline const T *operator->() const { return future->d.resultPointer(index); }
        inline const_iterator &operator++()
        { index = advanceIndex(index, 1); return *this; }
        inline const_iterator &operator--()
        { index = advanceIndex(index, -1); return *this; }
        inline const_iterator operator++(int)
        {
            const_iterator r = *this;
            index = advanceIndex(index, 1);
            return r;
        }
        inline const_iterator operator--(int)
        {
            const_iterator r = *this;
            index = advanceIndex(index, -1);
            return r;
        }
        inline const_iterator operator+(int j) const
        { return const_iterator(future, advanceIndex(index, j)); }
        inline const_iterator operator-(int j) const
        { return const_iterator(future, advanceIndex(index, -j)); }
        inline const_iterator &operator+=(int j)
        { index = advanceIndex(index, j); return *this; }
        inline const_iterator &operator-=(int j)
        { index = advanceIndex(index, -j); return *this; }
        friend inline const_iterator operator+(int j, const_iterator k)
        { return const_iterator(k.future, k.advanceIndex(k.index, j)); }
 
    private:
        friend bool comparesEqual(const const_iterator &lhs, const const_iterator &rhs) noexcept
        {
            return lhs.index == rhs.index;
        }
        Q_DECLARE_EQUALITY_COMPARABLE(const_iterator)
 
        
        int advanceIndex(int idx, int n) const
        {
            // The end iterator can be decremented, leave as-is for other cases
            if (idx == -1 && n >= 0)
                return idx;
 
            // Special case for decrementing the end iterator: wait for
            // finished to get the total result count.
            if (idx == -1 && future->isRunning())
                future->d.waitForFinished();
 
            // Wait for result at target index
            const int targetIndex = (idx == -1) ? future->resultCount() + n : idx + n;
            future->d.waitForResult(targetIndex);
 
            // After waiting there is either a result or the end was reached
            return (targetIndex < future->resultCount()) ? targetIndex : -1;
        }
 
        QFuture const * future;
        int index;
    };
    friend class const_iterator;
    typedef const_iterator ConstIterator;
 
    template<class U = T, typename = QtPrivate::EnableForNonVoid<U>>
    const_iterator begin() const { return  const_iterator(this, 0); }
 
    template<class U = T, typename = QtPrivate::EnableForNonVoid<U>>
    const_iterator constBegin() const { return  const_iterator(this, 0); }
 
    template<class U = T, typename = QtPrivate::EnableForNonVoid<U>>
    const_iterator end() const { return const_iterator(this, -1); }
 
    template<class U = T, typename = QtPrivate::EnableForNonVoid<U>>
    const_iterator constEnd() const { return const_iterator(this, -1); }
 
private:
    friend class QFutureWatcher<T>;
 
    template<class U>
    friend class QFuture;
 
    friend class QFutureInterfaceBase;
 
    template<class Function, class ResultType, class ParentResultType>
    friend class QtPrivate::Continuation;
 
    template<class Function, class ResultType>
    friend class QtPrivate::CanceledHandler;
 
#ifndef QT_NO_EXCEPTIONS
    template<class Function, class ResultType>
    friend class QtPrivate::FailureHandler;
#endif
 
    template<typename ResultType>
    friend struct QtPrivate::WhenAnyContext;
 
    friend struct QtPrivate::UnwrapHandler;
 
    using QFuturePrivate =
            std::conditional_t<std::is_same_v<T, void>, QFutureInterfaceBase, QFutureInterface<T>>;
 
#ifdef QFUTURE_TEST
public:
#endif
    mutable QFuturePrivate d;
};
 
template<typename T>
template<typename U, typename>
inline T QFuture<T>::result() const
{
    d.waitForResult(0);
    return d.resultReference(0);
}
 
template<typename T>
template<typename U, typename>
inline T QFuture<T>::resultAt(int index) const
{
    d.waitForResult(index);
    return d.resultReference(index);
}
 
template <typename T>
inline QFuture<T> QFutureInterface<T>::future()
{
    return QFuture<T>(this);
}
 
template<class T>
template<class Function>
QFuture<typename QFuture<T>::template ResultType<Function>> QFuture<T>::then(Function &&function)
{
    return then(QtFuture::Launch::Sync, std::forward<Function>(function));
}
 
template<class T>
template<class Function>
QFuture<typename QFuture<T>::template ResultType<Function>>
QFuture<T>::then(QtFuture::Launch policy, Function &&function)
{
    QFutureInterface<ResultType<Function>> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::Continuation<std::decay_t<Function>, ResultType<Function>, T>::create(
            std::forward<Function>(function), this, promise, policy);
    return promise.future();
}
 
template<class T>
template<class Function>
QFuture<typename QFuture<T>::template ResultType<Function>> QFuture<T>::then(QThreadPool *pool,
                                                                             Function &&function)
{
    QFutureInterface<ResultType<Function>> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::Continuation<std::decay_t<Function>, ResultType<Function>, T>::create(
            std::forward<Function>(function), this, promise, pool);
    return promise.future();
}
 
template<class T>
template<class Function>
QFuture<typename QFuture<T>::template ResultType<Function>> QFuture<T>::then(QObject *context,
                                                                             Function &&function)
{
    QFutureInterface<ResultType<Function>> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::Continuation<std::decay_t<Function>, ResultType<Function>, T>::create(
            std::forward<Function>(function), this, promise, context);
    return promise.future();
}
 
#ifndef QT_NO_EXCEPTIONS
template<class T>
template<class Function, typename>
QFuture<T> QFuture<T>::onFailed(Function &&handler)
{
    QFutureInterface<T> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::FailureHandler<std::decay_t<Function>, T>::create(std::forward<Function>(handler),
                                                                 this, promise);
    return promise.future();
}
 
template<class T>
template<class Function, typename>
QFuture<T> QFuture<T>::onFailed(QObject *context, Function &&handler)
{
    QFutureInterface<T> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::FailureHandler<std::decay_t<Function>, T>::create(std::forward<Function>(handler),
                                                                 this, promise, context);
    return promise.future();
}
 
#endif
 
template<class T>
template<class Function, typename>
QFuture<T> QFuture<T>::onCanceled(Function &&handler)
{
    QFutureInterface<T> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::CanceledHandler<std::decay_t<Function>, T>::create(std::forward<Function>(handler),
                                                                  this, promise);
    return promise.future();
}
 
template<class T>
template<class Function, typename>
QFuture<T> QFuture<T>::onCanceled(QObject *context, Function &&handler)
{
    QFutureInterface<T> promise(QFutureInterfaceBase::State::Pending);
    QtPrivate::CanceledHandler<std::decay_t<Function>, T>::create(std::forward<Function>(handler),
                                                                  this, promise, context);
    return promise.future();
}
 
template<class T>
template<class U, typename>
auto QFuture<T>::unwrap()
{
    if constexpr (QtPrivate::isQFutureV<typename QtPrivate::Future<T>::type>)
        return QtPrivate::UnwrapHandler::unwrapImpl(this).unwrap();
    else
        return QtPrivate::UnwrapHandler::unwrapImpl(this);
}
 
inline QFuture<void> QFutureInterface<void>::future()
{
    return QFuture<void>(this);
}
 
template<typename T>
QFutureInterfaceBase QFutureInterfaceBase::get(const QFuture<T> &future)
{
    return future.d;
}
 
namespace QtPrivate
{
 
template<typename T>
struct MetaTypeQFutureHelper<QFuture<T>>
{
    static bool registerConverter() {
        if constexpr (std::is_same_v<T, void>)
            return false;
 
        return QMetaType::registerConverter<QFuture<T>, QFuture<void>>(
                [](const QFuture<T> &future) { return QFuture<void>(future); });
    }
};
 
}  // namespace QtPrivate
 
namespace QtFuture {
 
#ifndef Q_QDOC
 
template<typename OutputSequence, typename InputIt,
         typename ValueType = typename std::iterator_traits<InputIt>::value_type,
         std::enable_if_t<std::conjunction_v<QtPrivate::IsForwardIterable<InputIt>,
                                             QtPrivate::IsRandomAccessible<OutputSequence>,
                                             QtPrivate::isQFuture<ValueType>>,
                          int> = 0>
QFuture<OutputSequence> whenAll(InputIt first, InputIt last)
{
    return QtPrivate::whenAllImpl<OutputSequence, InputIt, ValueType>(first, last);
}
 
template<typename InputIt, typename ValueType = typename std::iterator_traits<InputIt>::value_type,
         std::enable_if_t<std::conjunction_v<QtPrivate::IsForwardIterable<InputIt>,
                                             QtPrivate::isQFuture<ValueType>>,
                          int> = 0>
QFuture<QList<ValueType>> whenAll(InputIt first, InputIt last)
{
    return QtPrivate::whenAllImpl<QList<ValueType>, InputIt, ValueType>(first, last);
}
 
template<typename OutputSequence, typename... Futures,
         std::enable_if_t<std::conjunction_v<QtPrivate::IsRandomAccessible<OutputSequence>,
                                             QtPrivate::NotEmpty<Futures...>,
                                             QtPrivate::isQFuture<std::decay_t<Futures>>...>,
                          int> = 0>
QFuture<OutputSequence> whenAll(Futures &&... futures)
{
    return QtPrivate::whenAllImpl<OutputSequence, Futures...>(std::forward<Futures>(futures)...);
}
 
template<typename... Futures,
         std::enable_if_t<std::conjunction_v<QtPrivate::NotEmpty<Futures...>,
                                             QtPrivate::isQFuture<std::decay_t<Futures>>...>,
                          int> = 0>
QFuture<QList<std::variant<std::decay_t<Futures>...>>> whenAll(Futures &&... futures)
{
    return QtPrivate::whenAllImpl<QList<std::variant<std::decay_t<Futures>...>>, Futures...>(
            std::forward<Futures>(futures)...);
}
 
template<typename InputIt, typename ValueType = typename std::iterator_traits<InputIt>::value_type,
         std::enable_if_t<std::conjunction_v<QtPrivate::IsForwardIterable<InputIt>,
                                             QtPrivate::isQFuture<ValueType>>,
                          int> = 0>
QFuture<WhenAnyResult<typename QtPrivate::Future<ValueType>::type>> whenAny(InputIt first,
                                                                            InputIt last)
{
    return QtPrivate::whenAnyImpl<InputIt, ValueType>(first, last);
}
 
template<typename... Futures,
         std::enable_if_t<std::conjunction_v<QtPrivate::NotEmpty<Futures...>,
                                             QtPrivate::isQFuture<std::decay_t<Futures>>...>,
                          int> = 0>
QFuture<std::variant<std::decay_t<Futures>...>> whenAny(Futures &&... futures)
{
    return QtPrivate::whenAnyImpl(std::forward<Futures>(futures)...);
}
 
#else
 
template<typename OutputSequence, typename InputIt>
QFuture<OutputSequence> whenAll(InputIt first, InputIt last);
 
template<typename OutputSequence, typename... Futures>
QFuture<OutputSequence> whenAll(Futures &&... futures);
 
template<typename T, typename InputIt>
QFuture<QtFuture::WhenAnyResult<T>> whenAny(InputIt first, InputIt last);
 
template<typename... Futures>
QFuture<std::variant<std::decay_t<Futures>...>> whenAny(Futures &&... futures);
 
#endif // Q_QDOC
 
#if QT_DEPRECATED_SINCE(6, 10)
#if defined(Q_QDOC)
static QFuture<void> makeReadyFuture()
#else
template<typename T = void>
QT_DEPRECATED_VERSION_X(6, 10, "Use makeReadyVoidFuture() instead.")
static QFuture<T> makeReadyFuture()
#endif
{
    return makeReadyVoidFuture();
}
#endif // QT_DEPRECATED_SINCE(6, 10)
 
} // namespace QtFuture
 
Q_DECLARE_SEQUENTIAL_ITERATOR(Future)
 
QT_END_NAMESPACE
 
Q_DECLARE_METATYPE_TEMPLATE_1ARG(QFuture)
 
#endif // QFUTURE_H