Op 14/07/2016 om 17:10 schreef Olivier Goffart:
On Donnerstag, 14. Juli 2016 16:33:26 CEST Thomas Senyk wrote:
Hi,
I lately wanted to validate that a connecting&disconnecting to a lambda
will not leak the lambda object .. and found that more then that is leaked.
Here is my example: http://paste.ofcode.org/36dmWCT8ddF6Zaqb9csKZNv
After the 10million connections are executed and disconnected (all of
them a successful), I assume a drop in memory consumption and more
importantly a drop of cpu load to close to 0%.
I see neither one nor the other. I see continues 100% consume with no
memory consumption drop what so ever.
I did a quick peak into QMetaObject::activate and it seems no clean up
happened .. the list returned in
list = &connectionLists->at(signal_index);
(line #3660 in 5.6 checkout from today)
seems rather long! (10million?)
However all "if (!c->receiver)" shows no receiver and therefor will
continue right away .. at least
Is this expected? A bug? ... I'm happy to fill a bug report, I just
wanted to get some feedback, maybe I'm just doing something wrong
The lambda object and its capture is destroyed by the call to
slotObj->destroyIfLastRef()
The internal data structre (QObjectPrivate::Connection) is deleted by
QObjectPrivate::cleanConnectionLists which is actually only called when
a new connection is made to this object.
I don't think there is a leak, but it is true that some memory is only free'ed
when you add new connection or that the object is destroyed. (but the lambda
object is destroyed right after the disconnection)
Some background:
I wanted to check if a single-shot-connection (connection to a signal
and disconnect at first execute, using a lambda as slot) would be a
feasible thing to do.
You can do that already:
QTimer::sigleShot(100, [] { qDebug() << "hello"; });
That's not the same thing.
This looks like my earlier suggestion
https://bugreports.qt.io/browse/QTBUG-44219
André
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