Dear All,
I have an app that uses Cocoa and dispatch sources leaking a lot (ca. 5GB /
17h). The origin seems to come from a combination of dispatch sources, Bindings
& Core Animation. Below is a brief description of the app, what issues I
encounter and the related code.
DESCRIPTION OF THE APPLICATION
I have a scientific data acquisition App that is expected to run continuously
for a year and collect data every second from 144 sensors. The app is written
in Objective-C, targets MAC OS, and uses GCD a lot. Basically, I start several
dispatch queues running blocks to deal with scientific instruments connected to
different data buses. I use appropriate synchronization tools or locking
mechanisms to run everything safely and deal with concurrency.
ISSUES
At first, I did bind the 115 textfields (most having number formatters) on the
main view directly to the properties of the class instances representing
different physical scientific instruments. The issue was that it caused the UI
being refreshed from various threads while my app was operating (timer dispatch
sources manipulating the objects to collect data from instruments causing UI
refresh through bindings). I got the message "CoreAnimation: warning, deleted
thread with uncommitted CATransaction; set CA_DEBUG_TRANSACTIONS=1 in
environment to log backtraces” a lot.
So, I made a simple function (refreshUI) which transfers the data from
non-bound properties of the objects to bound-properties of the objects like
this :
// [myInstrument updateUI];
- (void)updateUI
{
assert([NSThread isMainThread]);
// LEFT: property of the object tied to the UI through bindings made
in IB
// RIGHT: as a quick fix: variable member of the object updated using a
background thread.
self.lastPT100Temperature = self->l_PT100Temperature;
self.lastPAAtmosphericPressure = self->l_PAAtmosphericPressure;
// etc...
}
This function is called once every second on the main thread like this :
- (void)startUIAutoUpdate
{
// @property (strong) dispatch_source_t uiRefreshTimer;
self.uiRefreshTimer =
dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,
dispatch_get_main_queue());
dispatch_source_set_timer(self.uiRefreshTimer, DISPATCH_TIME_NOW, 1.0 *
NSEC_PER_SEC, 0.25 * NSEC_PER_SEC);
__weak typeof(self) weakself = self;
dispatch_source_set_event_handler(self.uiRefreshTimer,
^{
@autoreleasepool
{
__strong typeof(weakself) strongself = weakself;
[strongself.myInstrument updateUI];
// etc...
}
};
dispatch_resume(self.uiRefreshTimer);
}
OBSERVATIONS
The app starts by taking around 25 MB of memory (reported by Activity monitor).
After 17h, I see around 5GB of memory used. After a few days… the app crashes.
On the other hand, if I comment the family of lines "[strongself.myInstrument
updateUI]", the app can run for a month using only 25-35 MB of memory. Data are
still collected every second and stored on disk of course, but not shown on
screen.
If I prevent my app from trying to communicate with the instruments (by not
instantiating the objects representing the communication interface) I can make
it run faster and take thousands of dummy data points a second (and store them
on the disk). The leaking issue is a little increased, but not by a factor of
1000. Only by a factor of 30 to 60. This is consistent with a UI refresh issue.
Additionally, I was unable to find any leaks with Instruments (but I barely
know how to use it) and the amount of memory reported by Instruments is far
less than the one reported by Activity monitor (but still, the system starts
swapping a lot after a while, so Activity monitor must be right). But
interestingly, when switching apps with CMD-TAB, Instruments shows memory jumps
(memory brutally decreases).
QUESTION
Well, I feel a little lost at this point. I lack the know-how to further
investigate the issue. Does anyone know what to try / measure / observe to get
more clues?
Best Regards,
Jean
-----------
Jean Suisse
Institut de Chimie Moléculaire de l’Université de Bourgogne
(ICMUB) — UMR 6302
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