Qt4-preview-feedback Archive, February 2008
Problems with deferred deletion of objects in 4.4 beta
Message 1 in thread
We're seeing significant memory leaks with 4.4 beta, and I
think I've found the reason why.
The change to note is in:
QEventDispatcherUNIX::processEvents(QEventLoop::ProcessEventsFlags
flags)
In the first few lines, I see this:
QCoreApplicationPrivate::sendPostedEvents(0, 0, d->threadData);
But in 4.3, I see this:
QCoreApplicationPrivate::sendPostedEvents(0, (flags &
QEventLoop::DeferredDeletion) ? -1 : 0, d->threadData);
The effect of this is to ignore the DeferredDeletion flag.
Down in QCoreApplicationPrivate::sendPostedEvents(), there's
a comment in beta 4.4:
void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int
event_type,
QThreadData *data)
{
if (event_type == -1) {
// we were called by an obsolete event dispatcher.
event_type = 0;
}
...
}
But in 4.3, I see this:
void QCoreApplicationPrivate::sendPostedEvents(QObject *receiver, int
event_type,
QThreadData *data)
{
bool doDeferredDeletion = (event_type == QEvent::DeferredDelete);
if (event_type == -1) {
// we were called by the event dispatcher.
doDeferredDeletion = true;
event_type = 0;
}
...
}
Does this mean we no longer need to clean up when our application shuts
down by calling qApp->processEvents(QEventLoop::DeferredDeletion)? If
so,
why are we getting so many leaked objects with 4.4 beta? Shouldn't they
get cleaned up automatically if they've been flagged for deferred
deletion?
Thanks,
Joe Newman
Synopsys, Inc.
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Message 2 in thread
Joe Newman wrote:
> We're seeing significant memory leaks with 4.4 beta, and I
> think I've found the reason why.
[snip]
>
> Does this mean we no longer need to clean up when our application shuts
> down by calling qApp->processEvents(QEventLoop::DeferredDeletion)?
DeferredDelete event handling has been improved to the point where most manual
deliver of such events is unnecessary[1]. As such, the DeferredDeletion
processEvents() flag has been deprecated and doesn't work anymore in 4.4. In
addition, it's just another way of calling sendPostedEvents(0,
QEvent::DeferredDelete); However, a gratuitous change like that isn't
necessarily a good thing. I'll fix it so that the flag continues to work.
[1] However, if you call deleteLater() on many objects after the event loop
has been stopped, it's still necessary to manual clean them up (as you
apparently do).
> If so, why are we getting so many leaked objects with 4.4 beta? Shouldn't they
> get cleaned up automatically if they've been flagged for deferred
> deletion?
If you replace qApp->processEvents(QEventLoop::DeferredDeletion) with
QApplication::sendPostedEvents(0, QEvent::DeferredDelete), does the leak go
away? If so, my revert of the QEventLoop::DeferredDeletion crippling will fix
your problem.
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