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Diffstat (limited to 'src/concurrent/qtconcurrentrun.cpp')
| -rw-r--r-- | src/concurrent/qtconcurrentrun.cpp | 236 |
1 files changed, 96 insertions, 140 deletions
diff --git a/src/concurrent/qtconcurrentrun.cpp b/src/concurrent/qtconcurrentrun.cpp index fecbb484ff..017f2df480 100644 --- a/src/concurrent/qtconcurrentrun.cpp +++ b/src/concurrent/qtconcurrentrun.cpp @@ -1,60 +1,28 @@ -/**************************************************************************** -** -** Copyright (C) 2016 The Qt Company Ltd. -** Contact: https://www.qt.io/licensing/ -** -** This file is part of the QtConcurrent module of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:LGPL$ -** Commercial License Usage -** Licensees holding valid commercial Qt licenses may use this file in -** accordance with the commercial license agreement provided with the -** Software or, alternatively, in accordance with the terms contained in -** a written agreement between you and The Qt Company. For licensing terms -** and conditions see https://www.qt.io/terms-conditions. For further -** information use the contact form at https://www.qt.io/contact-us. -** -** GNU Lesser General Public License Usage -** Alternatively, this file may be used under the terms of the GNU Lesser -** General Public License version 3 as published by the Free Software -** Foundation and appearing in the file LICENSE.LGPL3 included in the -** packaging of this file. Please review the following information to -** ensure the GNU Lesser General Public License version 3 requirements -** will be met: https://www.gnu.org/licenses/lgpl-3.0.html. -** -** GNU General Public License Usage -** Alternatively, this file may be used under the terms of the GNU -** General Public License version 2.0 or (at your option) the GNU General -** Public license version 3 or any later version approved by the KDE Free -** Qt Foundation. The licenses are as published by the Free Software -** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3 -** included in the packaging of this file. Please review the following -** information to ensure the GNU General Public License requirements will -** be met: https://www.gnu.org/licenses/gpl-2.0.html and -** https://www.gnu.org/licenses/gpl-3.0.html. -** -** $QT_END_LICENSE$ -** -****************************************************************************/ +// 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 /*! \page qtconcurrentrun.html - \title Concurrent Run and Run With Promise + \title Concurrent Run + \brief A simple way to run a task in a separate thread. \ingroup thread - The QtConcurrent::run() and QtConcurrent::runWithPromise() - functions run a function in a separate thread. + The QtConcurrent::run() function runs a function in a separate thread. The return value of the function is made available through the QFuture API. - The function passed to QtConcurrent::run() is able to report merely - a single computation result to its caller, while the function passed to - QtConcurrent::runWithPromise() can make use of the additional + + QtConcurrent::run() is an overloaded method. You can think of these overloads as slightly + different \e modes. + In \l {Concurrent Run (basic mode)} {basic mode}, the function passed to QtConcurrent::run() + is able to report merely a single computation result to its caller. + In \l {Concurrent Run With Promise} {run with promise mode}, the function passed to + QtConcurrent::run() can make use of the additional QPromise API, which enables multiple result reporting, progress reporting, suspending the computation when requested by the caller, or stopping the computation on the caller's demand. - These functions are part of the Qt Concurrent framework. + This function is a part of the Qt Concurrent framework. - \section1 Concurrent Run + \section1 Concurrent Run (basic mode) The function passed to QtConcurrent::run() may report the result through its return value. @@ -65,7 +33,7 @@ \snippet code/src_concurrent_qtconcurrentrun.cpp 0 - This will run \e aFunction in a separate thread obtained from the default + This will run \c aFunction in a separate thread obtained from the default QThreadPool. You can use the QFuture and QFutureWatcher classes to monitor the status of the function. @@ -86,12 +54,36 @@ the function. Changes made to the arguments after calling QtConcurrent::run() are \e not visible to the thread. + Note that QtConcurrent::run does not support calling overloaded functions + directly. For example, the code below won't compile: + +//! [run-with-overload-calls] + \snippet code/src_concurrent_qtconcurrentrun.cpp 15 + + The easiest workaround is to call the overloaded function through lambda: + + \snippet code/src_concurrent_qtconcurrentrun.cpp 16 + + Or you can tell the compiler which overload to choose by using a + \c static_cast: + + \snippet code/src_concurrent_qtconcurrentrun.cpp 17 + + Or qOverload: + + \snippet code/src_concurrent_qtconcurrentrun.cpp 18 +//! [run-with-overload-calls] + \section2 Returning Values from the Function Any return value from the function is available via QFuture: \snippet code/src_concurrent_qtconcurrentrun.cpp 2 + If you don't need the result (for example, because the function returns + \c{void}), using the QThreadPool::start() overload taking a function object + is more efficient. + As documented above, passing arguments is done like this: \snippet code/src_concurrent_qtconcurrentrun.cpp 3 @@ -135,8 +127,8 @@ \section1 Concurrent Run With Promise - The QtConcurrent::runWithPromise() enables more control - for the running task comparing to QtConcurrent::run(). + The \e {Run With Promise} mode enables more control for the running + task compared to \e basic mode of QtConcurrent::run(). It allows progress reporting of the running task, reporting multiple results, suspending the execution if it was requested, or canceling the task on caller's @@ -144,18 +136,17 @@ \section2 The mandatory QPromise argument - The function passed to QtConcurrent::runWithPromise() is expected - to have an additional argument of \e {QPromise<T> &} type, where - T is the type of the computation result (it should match the type T - of QFuture<T> returned by the QtConcurrent::runWithPromise()), like e.g.: + The function passed to QtConcurrent::run() in \e {Run With Promise} mode + is expected to have an additional argument of \c {QPromise<T> &} type, where + \c T is the type of the computation result (it should match the type \c T + of QFuture<T> returned by QtConcurrent::run()), like e.g.: \snippet code/src_concurrent_qtconcurrentrun.cpp 9 - The \e promise argument is instantiated inside the - QtConcurrent::runWithPromise() function, and its reference - is passed to the invoked \e aFunction, so the user - doesn't need to instantiate it by himself, nor pass it explicitly - when calling QtConcurrent::runWithPromise(). + The \c promise argument is instantiated inside the QtConcurrent::run() + function, and its reference is passed to the invoked \c aFunction, so the + user doesn't need to instantiate it, nor pass it explicitly + when calling QtConcurrent::run() in this mode. The additional argument of QPromise type always needs to appear as a first argument on function's arguments list, like: @@ -164,33 +155,42 @@ \section2 Reporting results - In contrast to QtConcurrent::run(), the function passed to - QtConcurrent::runWithPromise() is expected to always return void type. + In contrast to \e basic mode of QtConcurrent::run(), the function passed to + QtConcurrent::run() in \e {Run With Promise} mode is expected to always return void type. Result reporting is done through the additional argument of QPromise type. It also enables multiple result reporting, like: \snippet code/src_concurrent_qtconcurrentrun.cpp 11 + \note There's no need to call QPromise::start() and QPromise::finish() to + indicate the beginning and the end of computation (like you would normally do when + using QPromise). QtConcurrent::run() will always call them before starting and + after finishing the execution. + \section2 Suspending and canceling the execution The QPromise API also enables suspending and canceling the computation, if requested: \snippet code/src_concurrent_qtconcurrentrun.cpp 12 - The call to \e future.suspend() requests the running task to + The call to \c future.suspend() requests the running task to hold its execution. After calling this method, the running task - will suspend after the next call to \e promise.suspendIfRequested() + will suspend after the next call to \c promise.suspendIfRequested() in its iteration loop. In this case the running task will - block on a call to \e promise.suspendIfRequested(). The blocked - call will unblock after the \e future.resume() is called. + block on a call to \c promise.suspendIfRequested(). The blocked + call will unblock after the \c future.resume() is called. Note, that internally suspendIfRequested() uses wait condition in order to unblock, so the running thread goes into an idle state instead of wasting its resources when blocked in order to periodically check if the resume request came from the caller's thread. - The call to \e future.cancel() from the last line causes that the next - call to \e promise.isCanceled() will return \c true and - \e aFunction will return immediately without any further result reporting. + The call to \c future.cancel() from the last line causes that the next + call to \c promise.isCanceled() will return \c true and + \c aFunction will return immediately without any further result reporting. + + \note There's no need to call QPromise::finish() to stop the computation + after the cancellation (like you would normally do when using QPromise). + QtConcurrent::run() will always call it after finishing the execution. \section2 Progress reporting @@ -199,17 +199,17 @@ \snippet code/src_concurrent_qtconcurrentrun.cpp 13 - The caller installs the \e QFutureWatcher for the \e QFuture - returned by QtConcurrent::runWithPromise() in order to - connect to its \e progressValueChanged() signal and update + The caller installs the \c QFutureWatcher for the \c QFuture + returned by QtConcurrent::run() in order to + connect to its \c progressValueChanged() signal and update e.g. the graphical user interface accordingly. \section2 Invoking functions with overloaded operator()() - By default, QtConcurrent::runWithPromise() doesn't support functors with - overloaded operator()(). In case of overloaded functors the user - needs to explicitly specify the result type - as a template parameter passed to runWithPromise, like: + By default, QtConcurrent::run() doesn't support functors with + overloaded operator()() in \e {Run With Promise} mode. In case of overloaded + functors the user needs to explicitly specify the result type + as a template parameter passed to QtConcurrent::run(), like: \snippet code/src_concurrent_qtconcurrentrun.cpp 14 */ @@ -224,7 +224,7 @@ */ /*! - \fn QFuture<T> QtConcurrent::run(Function function, ...); + \fn template <typename T> QFuture<T> QtConcurrent::run(Function function, ...); Equivalent to \code @@ -235,81 +235,37 @@ QThreadPool. Note that \a function may not run immediately; \a function will only be run once a thread becomes available. - T is the same type as the return value of \a function. Non-void return - values can be accessed via the QFuture::result() function. +//! [run-description] + In \l {Concurrent Run (basic mode)} {basic mode} T is the same type as the return value + of \a function. Non-void return values can be accessed via the QFuture::result() function. - \note The QFuture returned can only be used to query for the - running/finished status and the return value of the function. In particular, + In \l {Concurrent Run (basic mode)} {basic mode} the QFuture returned can only be used to + query for the running/finished status and the return value of the function. In particular, canceling or pausing can be issued only if the computations behind the future has not been started. - \sa {Concurrent Run} -*/ - -/*! - \since 5.4 - \fn QFuture<T> QtConcurrent::run(QThreadPool *pool, Function function, ...); - - Runs \a function in a separate thread. The thread is taken from the - QThreadPool \a pool. Note that \a function may not run immediately; \a function - will only be run once a thread becomes available. - - T is the same type as the return value of \a function. Non-void return - values can be accessed via the QFuture::result() function. - - \note The QFuture returned can only be used to query for the - running/finished status and the return value of the function. In particular, - canceling or pausing can be issued only if the computations behind the future - has not been started. - - \sa {Concurrent Run} -*/ - -/*! - \since 6.0 - \fn QFuture<T> QtConcurrent::runWithPromise(Function function, ...); - - Equivalent to - \code - QtConcurrent::runWithPromise(QThreadPool::globalInstance(), function, ...); - \endcode - - Runs \a function in a separate thread. The thread is taken from the global - QThreadPool. Note that \a function may not run immediately; \a function - will only be run once a thread becomes available. - - The \a function is expected to return void - and must take an additional argument of \e {QPromise<T> &} type, + In \l {Concurrent Run With Promise} {run with promise mode}, the \a function is expected + to return void and must take an additional argument of \c {QPromise<T> &} type, placed as a first argument in function's argument list. T is the result type - and it is the same for the returned \e QFuture<T>. + and it is the same for the returned \c QFuture<T>. - Similar to QtConcurrent::run(), the QFuture returned can be used to query for the - running/finished status and the value reported by the function. In addition, - it may be used for suspending or canceling the running task, fetching - multiple results from the called /a function or monitoring progress - reported by the \a function. + In \l {Concurrent Run With Promise} {run with promise mode}, similar to \e basic mode, the + QFuture returned can be used to query for the running/finished status and the value reported + by the function. In addition, it may be used for suspending or canceling the + running task, fetching multiple results from the called \a function or + monitoring progress reported by the \a function. - \sa {Concurrent Run With Promise} + \sa {Concurrent Run (basic mode)}, {Concurrent Run With Promise}, QThreadPool::start() +//! [run-description] */ /*! - \since 6.0 - \fn QFuture<T> QtConcurrent::runWithPromise(QThreadPool *pool, Function function, ...); - - Runs \a function in a separate thread. The thread is taken from the - QThreadPool \a pool. Note that \a function may not run immediately; \a function - will only be run once a thread becomes available. - - The \a function is expected to return void - and must take an additional argument of \e {QPromise<T> &} type, - placed as a first argument in function's argument list. T is the result type - and it is the same for the returned \e QFuture<T>. + \since 5.4 + \fn template <typename T> QFuture<T> QtConcurrent::run(QThreadPool *pool, Function function, ...); - Similar to QtConcurrent::run(), the QFuture returned can be used to query for the - running/finished status and the value reported by the function. In addition, - it may be used for suspending or canceling the running task, fetching - multiple results from the called /a function or monitoring progress - reported by the \a function. + Schedules \a function on \a pool. Note that \a function may not run + immediately; \a function will only be run once a thread becomes available. - \sa {Concurrent Run With Promise} + \include qtconcurrentrun.cpp run-description */ + |