diff options
| author | Sze Howe Koh <szehowe.koh@gmail.com> | 2025-02-26 15:59:52 +0800 |
|---|---|---|
| committer | Sze Howe Koh <szehowe.koh@gmail.com> | 2025-02-27 14:21:06 +0800 |
| commit | f5b874fd2d393b783dad85c95a158383420e481a (patch) | |
| tree | fffa494f6650742657c511be840a99bf201fc6bc /src/corelib/kernel/qobject.cpp | |
| parent | 6fb39ca2cbb111469ce09c8342997eb5375e3239 (diff) | |
[Doc] QObject: Sync warnings of isSignalConnected() and receivers()
Extends e75c1a00e31723f1c9deb8427725fa0a58fae2a8 because calling
receivers() in disconnectNotify() can deadlock too.
As a drive-by, some statements are generalized further:
* "expensive initialization" -> "expensive operations" since that is
what the relevant snippets actually show.
* The potential race condition is not limited to "after this function
returns and before the signal gets emitted"
Task-number: QTBUG-106025
Change-Id: Iff014706b9e8d8147e3bbb9ac51542197eec5db3
Pick-to: 6.9 6.8 6.5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src/corelib/kernel/qobject.cpp')
| -rw-r--r-- | src/corelib/kernel/qobject.cpp | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp index 48baa96e104..54857f9f307 100644 --- a/src/corelib/kernel/qobject.cpp +++ b/src/corelib/kernel/qobject.cpp @@ -2735,10 +2735,16 @@ int QObject::senderSignalIndex() const \snippet code/src_corelib_kernel_qobject.cpp 21 + As the code snippet above illustrates, you can use this function to avoid + expensive operations or emitting a signal that nobody listens to. + + \warning In a multithreaded application, consecutive calls to this + function are not guaranteed to yield the same results. + \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. \sa isSignalConnected() */ @@ -2795,14 +2801,17 @@ 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 - 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. + expensive operations or emitting a signal that nobody listens to. + + \warning In a multithreaded application, consecutive calls to this + function are not guaranteed to yield the same results. \warning This function violates the object-oriented principle of modularity. In particular, this function must not be called from an override of connectNotify() or disconnectNotify(), as those might get called from any thread. + + \sa receivers() */ bool QObject::isSignalConnected(const QMetaMethod &signal) const { @@ -3486,8 +3495,7 @@ bool QObject::disconnect(const QObject *sender, const QMetaMethod &signal, \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. + an expensive operation only if something is connected to a signal. \warning This function is called from the thread which performs the connection, which may be a different thread from the thread in which |