diff options
Diffstat (limited to 'src/corelib/kernel/qobject.cpp')
| -rw-r--r-- | src/corelib/kernel/qobject.cpp | 33 |
1 files changed, 20 insertions, 13 deletions
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp index 1de6070388..0135b7a1b1 100644 --- a/src/corelib/kernel/qobject.cpp +++ b/src/corelib/kernel/qobject.cpp @@ -2620,13 +2620,15 @@ int QObject::receivers(const char *signal) const \snippet code/src_corelib_kernel_qobject.cpp 49 - As the code snippet above illustrates, you can use this function - to avoid emitting a signal that nobody listens to. + As the code snippet above illustrates, you can use this function to avoid + expensive initialization or emitting a signal that nobody listens to. + However, in a multithreaded application, connections might change after + this function returns and before the signal gets emitted. \warning This function violates the object-oriented principle of - modularity. However, it might be useful when you need to perform - expensive initialization only if something is connected to a - signal. + modularity. In particular, this function must not be called from an + override of connectNotify() or disconnectNotify(), as those might get + called from any thread. */ bool QObject::isSignalConnected(const QMetaMethod &signal) const { @@ -3308,8 +3310,13 @@ bool QObject::disconnect(const QObject *sender, const QMetaMethod &signal, signal. \warning This function is called from the thread which performs the - connection, which may be a different thread from the thread in - which this object lives. + connection, which may be a different thread from the thread in which + this object lives. This function may also be called with a QObject internal + mutex locked. It is therefore not allowed to re-enter any QObject + functions, including isSignalConnected(), from your reimplementation. If + you lock a mutex in your reimplementation, make sure that you don't call + QObject functions with that mutex held in other places or it will result in + a deadlock. \sa connect(), disconnectNotify() */ @@ -3338,12 +3345,12 @@ void QObject::connectNotify(const QMetaMethod &signal) expensive resources. \warning This function is called from the thread which performs the - disconnection, which may be a different thread from the thread in - which this object lives. This function may also be called with a QObject - internal mutex locked. It is therefore not allowed to re-enter any - of any QObject functions from your reimplementation and if you lock - a mutex in your reimplementation, make sure that you don't call QObject - functions with that mutex held in other places or it will result in + disconnection, which may be a different thread from the thread in which + this object lives. This function may also be called with a QObject internal + mutex locked. It is therefore not allowed to re-enter any QObject + functions, including isSignalConnected(), from your reimplementation. If + you lock a mutex in your reimplementation, make sure that you don't call + QObject functions with that mutex held in other places or it will result in a deadlock. \sa disconnect(), connectNotify() |