diff options
| author | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2023-06-24 12:39:43 +0200 |
|---|---|---|
| committer | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2023-06-24 19:09:30 +0200 |
| commit | 842cfcec80f9ddb20e6530e2dbbc71df68e96a94 (patch) | |
| tree | 9aa31c3aeb94dc0679b7150e9d9778c8cf262ad3 /src/corelib/kernel/qobject.cpp | |
| parent | 7297cd808b142c522d7d6bcfa30bf61a3a25127c (diff) | |
QObject: introduce QT_NO_CONTEXTLESS_CONNECT
The 3-arguments overload of connect() is error-prone / easy to misuse:
* it's easy to e.g. connect to a lambda, and capture local state in the
lambda. By not passing a receiver/context, the connection won't get
disconnected if the local state gets destroyed (effectively, it
creates a "dangling connection");
* in a multithread scenario, one may not realize that the connection is
forced to be direct. If the signal is emitted in another thread than
the one establishing the connection¹, then the functor will be invoked
in that other thread. (Not that "the thread establishing the
connection" has ever mattered, but again, this API is error-prone.)
Add a macro that allows users to disable the overload in their project.
I'm not going for deprecation because there's simply too much code
around that uses it.
[ChangeLog][QtCore][QObject] Added the QT_NO_CONTEXTLESS_CONNECT macro.
Defining the macro before including any Qt header will disable
the overload of QObject::connect that does not take a receiver/context
argument.
Change-Id: I86af1029c1a211ea365f417aae9038d3fcacadfd
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src/corelib/kernel/qobject.cpp')
| -rw-r--r-- | src/corelib/kernel/qobject.cpp | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp index 4304add49c6..e2c73d58ab7 100644 --- a/src/corelib/kernel/qobject.cpp +++ b/src/corelib/kernel/qobject.cpp @@ -4855,6 +4855,28 @@ QDebug operator<<(QDebug dbg, const QObject *o) */ /*! + \macro QT_NO_CONTEXTLESS_CONNECT + \relates QObject + \since 6.7 + + Defining this macro will the overload of QObject::connect() that + connects a signal to a functor, without also specifying a QObject + as a receiver/context object (that is, the 3-arguments overload + of QObject::connect()). + + Using the context-less overload is error prone, because it is easy + to connect to functors that depend on some local state of the + receiving end. If such local state gets destroyed, the connection + does not get automatically disconnected. + + Moreover, such connections are always direct connections, which may + cause issues in multithreaded scenarios (for instance, if the + signal is emitted from another thread). + + \sa QObject::connect, Qt::ConnectionType +*/ + +/*! \typedef QObjectList \relates QObject @@ -4959,6 +4981,11 @@ void qDeleteInEventHandler(QObject *o) However, you should take care that any objects used within the functor are still alive when the signal is emitted. + For this reason, it is recommended to use the overload of connect() + that also takes a QObject as a receiver/context. It is possible + to disable the usage of the context-less overload by defining the + \c{QT_NO_CONTEXTLESS_CONNECT} macro. + Overloaded functions can be resolved with help of \l qOverload. */ |