// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page qtconcurrent-index.html
    \title Qt Concurrent

    \brief The Qt Concurrent module contains functionality to support concurrent execution of program code.


    The Qt Concurrent module provides high-level APIs that make it
    possible to write multi-threaded programs without using low-level
    threading primitives such as mutexes, read-write locks, wait
    conditions, or semaphores. Programs written with Qt Concurrent
    automatically adjust the number of threads used according to the
    number of processor cores available. This means that applications
    written today will continue to scale when deployed on multi-core
    systems in the future.

    Qt Concurrent includes functional programming style APIs for
    parallel list processing, including a MapReduce and FilterReduce
    implementation for shared-memory (non-distributed) systems, and
    classes for managing asynchronous computations in GUI
    applications:

    \list
    \li \l {Concurrent Map and Map-Reduce}
        \list
            \li \l {QtConcurrent::map}{QtConcurrent::map()} applies a function
                to every item in a container, modifying the items in-place.
            \li \l {QtConcurrent::mapped}{QtConcurrent::mapped()} is like
                map(), except that it returns a new container with the
                modifications.
            \li \l {QtConcurrent::mappedReduced}{QtConcurrent::mappedReduced()}
                is like mapped(), except that the modified results are reduced
                or folded into a single result.
        \endlist

    \li \l {Concurrent Filter and Filter-Reduce}
    \list
        \li \l {QtConcurrent::filter}{QtConcurrent::filter()} removes all items
            from a container based on the result of a filter function.
        \li \l {QtConcurrent::filtered}{QtConcurrent::filtered()} is like
            filter(), except that it returns a new container with the filtered
            results.
        \li \l {QtConcurrent::filteredReduced}{QtConcurrent::filteredReduced()}
            is like filtered(), except that the filtered results are reduced or
            folded into a single result.
    \endlist

    \li \l {Concurrent Run}
    \list
        \li \l {QtConcurrent::run}{QtConcurrent::run()} runs a function in
            another thread.
    \endlist

    \li \l {Concurrent Task}
    \list
        \li \l {QtConcurrent::task}{QtConcurrent::task()} creates an instance
            of QtConcurrent::QTaskBuilder. This object can be used for adjusting
            parameters and for kicking off a task in a separate thread.
    \endlist

    \li QFuture represents the result of an asynchronous computation.

    \li QFutureIterator allows iterating through results available via QFuture.

    \li QFutureWatcher allows monitoring a QFuture using signals-and-slots.

    \li QFutureSynchronizer is a convenience class that automatically
    synchronizes several QFutures.

    \li QPromise provides a way to report progress and results of the
    asynchronous computation to QFuture. Allows suspending or canceling the task
    when requested by QFuture.

    \endlist

    Qt Concurrent supports several STL-compatible container and iterator types,
    but works best with Qt containers that have random-access iterators, such as
    QList. The map and filter functions accept both containers and begin/end
    iterators.

    STL Iterator support overview:

    \table
    \header
        \li Iterator Type
        \li Example classes
        \li Support status
    \row
        \li Input Iterator
        \li
        \li Not Supported
    \row
        \li Output Iterator
        \li
        \li Not Supported
    \row
        \li Forward Iterator
        \li std::slist
        \li Supported
    \row
        \li Bidirectional Iterator
        \li std::list
        \li Supported
    \row
        \li Random Access Iterator
        \li QList, std::vector
        \li Supported and Recommended
    \endtable

    Random access iterators can be faster in cases where Qt Concurrent is
    iterating over a large number of lightweight items, since they allow
    skipping to any point in the container. In addition, using random access
    iterators allows Qt Concurrent to provide progress information through
     QFuture::progressValue() and QFutureWatcher::progressValueChanged().

    The non in-place modifying functions such as mapped() and filtered() makes a
    copy of the container when called. If you are using STL containers this copy
    operation might take some time, in this case we recommend specifying the
    begin and end iterators for the container instead.


    \include module-use.qdocinc using qt module
    \snippet snippets/CMakeLists.txt cmake_use

    See also the \l {Build with CMake} overview.

    \include module-use.qdocinc building with qmake
    \snippet snippets/snippets.pro qmake_use

    \section1 Module Evolution
    \l{Changes to Qt Concurrent} lists important changes in the module API
    and functionality that were done for the Qt 6 series of Qt.

    \section1 Licenses

    The Qt Concurrent module is available under commercial licenses from
    \l{The Qt Company}.
    In addition, it is available under free software licenses:
    The \l{GNU Lesser General Public License, version 3}, or
    the \l{GNU General Public License, version 2}.
    See \l{Qt Licensing} for further details.
*/
