Qt
Internal/Contributor docs for the Qt SDK. Note: These are NOT official API docs; those are found at https://doc.qt.io/
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genustypes.h File Reference

(d364f2a5a80bf7bc52a7717866e677f1c40fd696)

#include <QtGlobal>
#include <type_traits>
Include dependency graph for genustypes.h:
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Enumerations

enum class  Genus : unsigned char {
  DontCare = 0x0 , CPP = 0x1 , QML = 0x4 , DOC = 0x8 ,
  API = CPP | QML
}
 \title Genus and NodeType enumerations More...
enum class  NodeType : unsigned char {
  NoType , Namespace , Class , Struct ,
  Union , HeaderFile , Page , Enum ,
  Example , ExternalPage , Function , Typedef ,
  TypeAlias , Property , Variable , Group ,
  Module , QmlEnum , QmlType , QmlModule ,
  QmlProperty , QmlValueType , SharedComment , Collection ,
  Proxy
}

Enumeration Type Documentation

◆ Genus

enum class Genus : unsigned char
strong

\title Genus and NodeType enumerations

This header file defines two main enumerations:

  • \l {Genus}: An unsigned char type that specifies whether a node in the documentation represents a C++ element, a QML element, a text document, or a combination used to indicate API types.
  • \l {NodeType}: An unsigned char type that identifies the precise subclass of a node, such as Namespace, Class, Function, etc.

In addition, the file provides two inline utility functions:

  • \l hasCommonGenusType(), which performs a bitwise comparison between two Genus values to determine if they share any common bits.
  • \l isApiGenus(), which checks if a given Genus value represents an API type by verifying if it contains the C++ or QML flags.

These enumerations and functions are used in QDoc to facilitate mapping of source elements to node categories, as well as to enable fine-grained search and filtering based on node types.

An unsigned char value that specifies whether the Node represents a C++ element, a QML element, or a text document. The Genus values are also passed to search functions to specify the Genus of Tree Node that can satisfy the search.

\value DontCare The Genus is not specified. Used when calling Tree search functions to indicate the search can accept any Genus of Node. \value CPP The Node represents a C++ element. \value QML The Node represents a QML element. \value DOC The Node represents a text document. \value API The Node represents an API element.

Enumerator
DontCare 
CPP 
QML 
DOC 
API 

Definition at line 53 of file genustypes.h.

◆ NodeType

enum class NodeType : unsigned char
strong
Enumerator
NoType 
Namespace 
Class 
Struct 
Union 
HeaderFile 
Page 
Enum 
Example 
ExternalPage 
Function 
\page qtconcurrentrun.html
\title Concurrent Run
\brief A simple way to run a task in a separate thread.
\ingroup 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.

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.

This function is a part of the Qt Concurrent framework.

\section1 Optimize includes

If you include the \c <QtConcurrent> header, the entire Qt Concurrent
module with the entire Qt Core module will be included, which may increase
compilation times and binary sizes. To use the
\l {QtConcurrent::run}{QtConcurrent::run()} function, you can include a
more specific header:

\code
#include <QtConcurrentRun>
\endcode

\section1 Concurrent Run (basic mode)

The function passed to QtConcurrent::run() may report the result
through its return value.

\section2 Running a Function in a Separate Thread

To run a function in another thread, use QtConcurrent::run():

\snippet code/src_concurrent_qtconcurrentrun.cpp 0

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.

To use a dedicated thread pool, you can pass the QThreadPool as
the first argument:

\snippet code/src_concurrent_qtconcurrentrun.cpp explicit-pool-0

\section2 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 code/src_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.

Note that QtConcurrent::run does not support calling overloaded functions
directly. For example, the code below won't compile:

! [run-with-overload-calls]

void foo(int arg);
void foo(int arg1, int arg2);
...
QFuture<void> future = QtConcurrent::run(foo, 42);

The easiest workaround is to call the overloaded function through lambda:

QFuture<void> future = QtConcurrent::run([] { foo(42); });

Or you can tell the compiler which overload to choose by using a static_cast:

QFuture<void> future = QtConcurrent::run(static_cast<void(*)(int)>(foo), 42);

Or qOverload:

QFuture<void> future = QtConcurrent::run(qOverload<int>(foo), 42);

! [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

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.

\section2 Additional API Features

\section3 Using Member Functions

QtConcurrent::run() also accepts pointers to member functions.
In Qt 6, the first argument must be the pointer to the member function,
followed by either a const reference or a pointer to an instance of the
class. Passing a const reference is useful when calling const member
functions; passing a 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 code/src_concurrent_qtconcurrentrun.cpp 4

Calling a non-const member function is done like this:

\snippet code/src_concurrent_qtconcurrentrun.cpp 5

\section3 Using Lambda Functions

Calling a lambda function is done like this:

\snippet code/src_concurrent_qtconcurrentrun.cpp 6

Calling a function modifies an object passed by reference is done like this:

\snippet code/src_concurrent_qtconcurrentrun.cpp 7

Using callable object is done like this:

\snippet code/src_concurrent_qtconcurrentrun.cpp 8

\section1 Concurrent Run With Promise

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
demand.

\section2 The mandatory QPromise argument

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 \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:

\snippet code/src_concurrent_qtconcurrentrun.cpp 10

\section2 Reporting results

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 \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 \c promise.suspendIfRequested()
in its iteration loop. In this case the running task will
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 \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

It's also possible to report the progress of a task
independently of result reporting, like:

\snippet code/src_concurrent_qtconcurrentrun.cpp 13

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::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

This typedef is a dummy required to make the Function type name known so that clang doesn't reject functions that use it.

Typedef 
TypeAlias 
Property 
Variable 
Group 
Module 
QmlEnum 
QmlType 
QmlModule 
QmlProperty 
QmlValueType 
SharedComment 
Collection 
Proxy 

Definition at line 150 of file genustypes.h.