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/*! \class QFuture

    \threadsafe

    \brief The QFuture class represents the result of an asynchronous computation.

    \since 4.4

    \ingroup thread

    To start a computation, use one of the APIs in the

    \l {Concurrent Programming}{Qt Concurrent} framework.

    QFuture allows threads to be synchronized against one or more results

    which will be ready at a later point in time. The result can be of any type

    that has a default constructor and a copy constructor. If a result is not

    available at the time of calling the result(), resultAt(), or results()

    functions, QFuture will wait until the result becomes available. You can

    use the isResultReadyAt() function to determine if a result is ready or

    not. For QFuture objects that report more than one result, the

    resultCount() function returns the number of continuous results. This

    means that it is always safe to iterate through the results from 0 to 

    resultCount().

    QFuture provides a \l{Java-style iterators}{Java-style iterator}

    (QFutureIterator) and an \l{STL-style iterators}{STL-style iterator}

    (QFuture::const_iterator). Using these iterators is  another way to access

    results in the future.

    QFuture also offers ways to interact with a runnning computation. For

    instance, the computation can be canceled with the cancel() function. To

    pause the computation, use the setPaused() function or one of the pause(),

    resume(), or togglePaused() convenience functions. Be aware that not all

    asynchronous computations can be canceled or paused. For example, the

    future returned by QtConcurrent::run() cannot be canceled; but the

    future returned by QtConcurrent::mappedReduced() can.

    Progress information is provided by the progressValue(),

    progressMinimum(), progressMaximum(), and progressText() functions. The

    waitForFinished() function causes the calling thread to block and wait for

    the computation to finish, ensuring that all results are available.

    The state of the computation represented by a QFuture can be queried using

    the isCanceled(), isStarted(), isFinished(), isRunning(), or isPaused()

    functions.

    QFuture is a lightweight reference counted class that can be passed by

    value.

    QFuture<void> is specialized to not contain any of the result fetching

    functions. Any QFuture<T> can be assigned or copied into a QFuture<void>

    as well. This is useful if only status or progress information is needed

    - not the actual result data.

    To interact with running tasks using signals and slots, use QFutureWatcher.

    \sa QFutureWatcher, {Concurrent Programming}{Qt Concurrent}

*/

/*! \fn QFuture::QFuture()

    Constructs an empty future.

*/

/*! \fn QFuture::QFuture(const QFuture &other)

    Constructs a copy of \a other.

    \sa operator=()

*/

/*! \fn QFuture::QFuture(QFutureInterface<T> *resultHolder)

    \internal

*/

/*! \fn QFuture::~QFuture()

    Destroys the future.

    Note that this neither waits nor cancels the asynchronous computation. Use

    waitForFinished() or QFutureSynchronizer when you need to ensure that the

    computation is completed before the future is destroyed.

*/

/*! \fn QFuture &QFuture::operator=(const QFuture &other)

     Assigns \a other to this future and returns a reference to this future.

*/

/*! \fn bool QFuture::operator==(const QFuture &other) const

    Returns true if \a other is a copy of this future; otherwise returns false.

*/

/*! \fn bool QFuture::operator!=(const QFuture &other) const

    Returns true if \a other is \e not a copy of this future; otherwise returns

    false.

*/

/*! \fn void QFuture::cancel()

    Cancels the asynchronous computation represented by this future. Note that

    the cancelation is asynchronous. Use waitForFinished() after calling

    cancel() when you need synchronous cancelation.

    Results currently available may still be accessed on a canceled future,

    but new results will \e not become available after calling this function.

    Any QFutureWatcher object that is watching this future will not deliver

    progress and result ready signals on a canceled future.

    Be aware that not all asynchronous computations can be canceled. For

    example, the future returned by QtConcurrent::run() cannot be canceled;

    but the future returned by QtConcurrent::mappedReduced() can.

*/

/*! \fn bool QFuture::isCanceled() const

    Returns true if the asynchronous computation has been canceled with the

    cancel() function; otherwise returns false.

    Be aware that the computation may still be running even though this

    function returns true. See cancel() for more details.

*/

/*! \fn void QFuture::setPaused(bool paused)

    If \a paused is true, this function pauses the asynchronous computation

    represented by the future. If the computation is  already paused, this

    function does nothing. Any QFutureWatcher object that is watching this

    future will stop delivering progress and result ready signals while the

    future is paused. Signal delivery will continue once the future is

    resumed.

    If \a paused is false, this function resumes the asynchronous computation.

    If the computation was not previously paused, this function does nothing.

    Be aware that not all computations can be paused. For example, the future

    returned by QtConcurrent::run() cannot be paused; but the future returned

    by QtConcurrent::mappedReduced() can.

    \sa pause(), resume(), togglePaused()

*/

/*! \fn bool QFuture::isPaused() const

    Returns true if the asynchronous computation has been paused with the

    pause() function; otherwise returns false.

    Be aware that the computation may still be running even though this

    function returns true. See setPaused() for more details.

    \sa setPaused(), togglePaused()

*/

/*! \fn void QFuture::pause()

    Pauses the asynchronous computation represented by this future. This is a

    convenience method that simply calls setPaused(true).

    \sa resume()

*/

/*! \fn void QFuture::resume()

    Resumes the asynchronous computation represented by this future. This is a

    convenience method that simply calls setPaused(false).

    \sa pause()

*/

/*! \fn void QFuture::togglePaused()

    Toggles the paused state of the asynchronous computation. In other words,

    if the computation is currently paused, calling this function resumes it;

    if the computation is running, it is paused. This is a convenience method

    for calling setPaused(!isPaused()).

    \sa setPaused(), pause(), resume()

*/

/*! \fn bool QFuture::isStarted() const

    Returns true if the asynchronous computation represented by this future

    has been started; otherwise returns false.

*/

/*! \fn bool QFuture::isFinished() const

    Returns true if the asynchronous computation represented by this future

    has finished; otherwise returns false.

*/

/*! \fn bool QFuture::isRunning() const

    Returns true if the asynchronous computation represented by this future is

    currently running; otherwise returns false.

*/

/*! \fn int QFuture::resultCount() const

    Returns the number of continuous results available in this future. The real

    number of results stored might be different from this value, due to gaps

    in the result set. It is always safe to iterate through the results from 0

    to resultCount().

    \sa result(), resultAt(), results()

*/

/*! \fn int QFuture::progressValue() const

    Returns the current progress value, which is between the progressMinimum()

    and progressMaximum().

    \sa progressMinimum(), progressMaximum()

*/

/*! \fn int QFuture::progressMinimum() const

    Returns the minimum progressValue().

    \sa progressValue(), progressMaximum()

*/

/*! \fn int QFuture::progressMaximum() const

    Returns the maximum progressValue().

    \sa progressValue(), progressMinimum()

*/

/*! \fn QString QFuture::progressText() const

    Returns the (optional) textual representation of the progress as reported

    by the asynchronous computation.

    Be aware that not all computations provide a textual representation of the

    progress, and as such, this function may return an empty string.

*/

/*! \fn void QFuture::waitForFinished()

    Waits for the asynchronous computation to finish (including cancel()ed

    computations).

*/

/*! \fn T QFuture::result() const

    Returns the first result in the future. If the result is not immediately

    available, this function will block and wait for the result to become

    available. This is a convenience method for calling resultAt(0).

    \sa resultAt(), results()

*/

/*! \fn T QFuture::resultAt(int index) const

    Returns the result at \a index in the future. If the result is not

    immediately available, this function will block and wait for the result to

    become available.

    \sa result(), results(), resultCount()

*/

/*! \fn bool QFuture::isResultReadyAt(int index) const

    Returns true if the result at \a index is immediately available; otherwise

    returns false.

    \sa resultAt(), resultCount()

*/

/*! \fn QFuture::operator T() const

    Returns the first result in the future. If the result is not immediately

    available, this function will block and wait for the result to become

    available. This is a convenience method for calling result() or

    resultAt(0).

    \sa result(), resultAt(), results()

*/

/*! \fn QList<T> QFuture::results() const

    Returns all results from the future. If the results are not immediately

    available, this function will block and wait for them to become available.

    \sa result(), resultAt(), resultCount()

*/

/*! \fn QFuture::const_iterator QFuture::begin() const

    Returns a const \l{STL-style iterator} pointing to the first result in the

    future.

    \sa constBegin(), end()

*/

/*! \fn QFuture::const_iterator QFuture::end() const

    Returns a const \l{STL-style iterator} pointing to the imaginary result

    after the last result in the future.

    \sa begin(), constEnd()

*/

/*! \fn QFuture::const_iterator QFuture::constBegin() const

    Returns a const \l{STL-style iterator} pointing to the first result in the

    future.

    \sa begin(), constEnd()

*/

/*! \fn QFuture::const_iterator QFuture::constEnd() const

    Returns a const \l{STL-style iterator} pointing to the imaginary result

    after the last result in the future.

    \sa constBegin(), end()

*/

/*! \class QFuture::const_iterator

    \reentrant

    \since 4.4

    \brief The QFuture::const_iterator class provides an STL-style const

    iterator for QFuture.

    QFuture provides both \l{STL-style iterators} and \l{Java-style iterators}.

    The STL-style iterators are more low-level and more cumbersome to use; on

    the other hand, they are slightly faster and, for developers who already

    know STL, have the advantage of familiarity.

    The default QFuture::const_iterator constructor creates an uninitialized

    iterator. You must initialize it using a QFuture function like

    QFuture::constBegin() or QFuture::constEnd() before you start iterating.

    Here's a typical loop that prints all the results available in a future:

    \snippet doc/src/snippets/code/src_corelib_concurrent_qfuture.cpp 0

    \sa QFutureIterator, QFuture

*/

/*! \typedef QFuture::const_iterator::iterator_category

    Typedef for std::bidirectional_iterator_tag. Provided for STL compatibility.

*/

/*! \typedef QFuture::const_iterator::difference_type

    Typedef for ptrdiff_t. Provided for STL compatibility.

*/

/*! \typedef QFuture::const_iterator::value_type

    Typedef for T. Provided for STL compatibility.

*/

/*! \typedef QFuture::const_iterator::pointer

    Typedef for const T *. Provided for STL compatibility.

*/

/*! \typedef QFuture::const_iterator::reference

    Typedef for const T &. Provided for STL compatibility.

*/

/*! \fn QFuture::const_iterator::const_iterator()

    Constructs an uninitialized iterator.

    Functions like operator*() and operator++() should not be called on an

    uninitialized iterartor. Use operator=() to assign a value to it before

    using it.

    \sa QFuture::constBegin() QFuture::constEnd()

*/

/*! \fn QFuture::const_iterator::const_iterator(QFuture const * const future, int index)

    \internal

*/

/*! \fn QFuture::const_iterator::const_iterator(const const_iterator &other)

    Constructs a copy of \a other.

*/

/*! \fn QFuture::const_iterator &QFuture::const_iterator::operator=(const const_iterator &other)

    Assigns \a other to this iterator.

*/

/*! \fn const T &QFuture::const_iterator::operator*() const

    Returns the current result.

*/

/*! \fn const T *QFuture::const_iterator::operator->() const

    Returns a pointer to the current result.

*/

/*! \fn bool QFuture::const_iterator::operator!=(const const_iterator &other) const

    Returns true if \a other points to a different result than this iterator;

    otherwise returns false.

    \sa operator==()

*/

/*! \fn bool QFuture::const_iterator::operator==(const const_iterator &other) const

    Returns true if \a other points to the same result as this iterator;

    otherwise returns false.

    \sa operator!=()

*/

/*! \fn QFuture::const_iterator &QFuture::const_iterator::operator++()

    The prefix ++ operator (\c{++it}) advances the iterator to the next result

    in the future and returns an iterator to the new current result.

    Calling this function on QFuture::constEnd() leads to undefined results.

    \sa operator--()

*/

/*! \fn QFuture::const_iterator QFuture::const_iterator::operator++(int)

    \overload

    The postfix ++ operator (\c{it++}) advances the iterator to the next

    result in the future and returns an iterator to the previously current

    result.

*/

/*! \fn QFuture::const_iterator &QFuture::const_iterator::operator--()

    The prefix -- operator (\c{--it}) makes the preceding result current and

    returns an iterator to the new current result.

    Calling this function on QFuture::constBegin() leads to undefined results.

    \sa operator++()

*/

/*! \fn QFuture::const_iterator QFuture::const_iterator::operator--(int)

    \overload

    The postfix -- operator (\c{it--}) makes the preceding result current and

    returns an iterator to the previously current result.

*/

/*! \fn QFuture::const_iterator &QFuture::const_iterator::operator+=(int j)

    Advances the iterator by \a j results. (If \a j is negative, the iterator

    goes backward.)

    \sa operator-=(), operator+()

*/

/*! \fn QFuture::const_iterator &QFuture::const_iterator::operator-=(int j)

    Makes the iterator go back by \a j results. (If \a j is negative, the

    iterator goes forward.)

    \sa operator+=(), operator-()

*/

/*! \fn QFuture::const_iterator QFuture::const_iterator::operator+(int j) const

    Returns an iterator to the results at \a j positions forward from this

    iterator. (If \a j is negative, the iterator goes backward.)

    \sa operator-(), operator+=()

*/

/*! \fn QFuture::const_iterator QFuture::const_iterator::operator-(int j) const

    Returns an iterator to the result at \a j positions backward from this

    iterator. (If \a j is negative, the iterator goes forward.)

    \sa operator+(), operator-=()

*/

/*! \typedef QFuture::ConstIterator