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/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the QtCore 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 Digia. For licensing terms and
** conditions see http://qt.digia.com/licensing. For further information
** use the contact form at http://qt.digia.com/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 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Digia gives you certain additional
** rights. These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\headerfile <QtConcurrentRun>
\title Asynchronous Run
\brief The <QtConcurrentRun> header provides a way to run a function in a
separate thread.
\ingroup thread
This function is a part of the \l {Concurrent Programming}{Qt Concurrent} framework.
The QtConcurrent::run() function runs a function in a separate thread.
The return value of the function is made available through the QFuture API.
\section1 Running a Function in a Separate Thread
To run a function in another thread, use QtConcurrent::run():
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 0
This will run \e 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.
\section1 Passing Arguments to the Function
Passing arguments to the function is done by adding them to the
QtConcurrent::run() call immediately after the function name. For example:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 1
A copy of each argument is made at the point where QtConcurrent::run() is
called, and these values are passed to the thread when it begins executing
the function. Changes made to the arguments after calling
QtConcurrent::run() are \e not visible to the thread.
\section1 Returning Values from the Function
Any return value from the function is available via QFuture:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 2
As documented above, passing arguments is done like this:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 3
Note that the QFuture::result() function blocks and waits for the result
to become available. Use QFutureWatcher to get notification when the
function has finished execution and the result is available.
\section1 Additional API Features
\section2 Using Member Functions
QtConcurrent::run() also accepts pointers to member functions. The first
argument must be either a const reference or a pointer to an instance of
the class. Passing by const reference is useful when calling const member
functions; passing by pointer is useful for calling non-const member
functions that modify the instance.
For example, calling QByteArray::split() (a const member function) in a
separate thread is done like this:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 4
Calling a non-const member function is done like this:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 5
\section2 Using Bound Function Arguments
Note that Qt does not provide support for bound functions. This is
provided by 3rd party libraries like
\l{http://www.boost.org/libs/bind/bind.html}{Boost} or
\l{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf}
{C++ TR1 Library Extensions}.
You can use boost::bind() or std::tr1::bind() to \e bind a number of
arguments to a function when called. There are number of reasons for doing
this:
\list
\o To call a function that takes more than 5 arguments.
\o To simplify calling a function with constant arguments.
\o Changing the order of arguments.
\endlist
See the documentation for the relevant functions for details on how to use
the bind API.
Calling a bound function is done like this:
\snippet doc/src/snippets/code/src_corelib_concurrent_qtconcurrentrun.cpp 6
*/
/*!
\fn QFuture<T> QtConcurrent::run(Function function, ...);
\relates <QtConcurrentRun>
Runs \a function in a separate thread. The thread is taken from the global
QThreadPool. Note that the function may not run immediately; the function
will only be run when a thread is 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 that the QFuture returned by QtConcurrent::run() does not support
canceling, pausing, or progress reporting. The QFuture returned can only
be used to query for the running/finished status and the return value of
the function.
*/
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