LowMemory & Apple Instruments

Targets iOS
#1

Hi there! I’m getting lots of low memory errors with my app. So I decided to try Apple Instruments to see where the problem might be. The first problem is: I don’t understand Apple Instruments :exploding_head:

I connected my iPhone to the MacBook and started Apple Instruments, selecting “Allocations”. Then I started my app. So my question is: the column “Persistent” shows the memory that’s being allocated to the app, right? So that’s the one I need to bring down. Is this correct? I have attached a screenshot.

If so, I don’t understand these two things:

  1. “Persistent” values are going up while the app is open although the app does nothing. I am just looking at the app and don’t touch it but the memory is going up slowly. What does that mean? Is there something running in the background?

  2. When I open a view showing a few iOS Table Cells with images on it, the memory goes up. As expected I guess. When I close the view I had assumed that the images are being released from the memory automatically and I don’t have to worry about them any longer. That doesn’t seem to be the case because the memory never goes down (regardless of what I do). How do I handle these things? Do I need to kill every image ever shown from memory when I close a view?

Thank you already!
Christoph

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#2

If you close a view but retain an instance of a picture somewhere then the memory won’t be released.

Or if you have a circular reference somewhere perhaps this could happen

#3

Please check out my blog on a series on Instruments: https://www.mothsoftware.com/blog/blog.php?search=instruments .

I have more experience with Leaks instead of Allocations. Leaks can show you if you don’t release memory.

1 Like
#4

I’d used instruments a fair amount before reading Beatrix’s blog posts and I learned a lot from them.

Great resource. Thanks much for sharing this with the community @Beatrix_Willius!

#5

That’s a good point, thank you. I believe I still have instances of these pictures open but I don’t know how to remove/release them. This is how the view looks like (I’m still calling it iOSView because the project has not been converted to API2.0 yet):
iOSView -> iOSTable -> multiple instances of the same iOSCustomTableCell with multiple iOSImageViews controls on it.

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When I close this view I would assume all the controls on it are being released from memory. The problem might be the iOSCustomTableCell because it’s “global”. Is there a way to make the iOSCustomTableCells “local” so that they will get deconstructed when closing the view? Or do I have to remove each instance of the iOSCustomTableCell one-by-one? I tried removing the iOSTable but that won’t change the memory allocation.

#6

Are you using a datasource for displaying the cells?

#7

I don’t. I am using custom table cells. I don’t think it’s possible to use custom table cells with datasource, is it?

#8

Oh, and happy new year to all of you!

#9

Happy new year to you too.

Of course it is possible to use a datasource with custom table cells and it is highly recommended.

#10

Thank you Jeremie, I’ll try that.

Still, if there are no tables on the view, the view and its content is still being kept in memory when I close it. So if I have 4 pictures 1 MB each on a view, 4 MB of memory will be added to the app’s memory usage every time I open the view. I would expect those 4 MB being released from memory when I close the view but that doesn’t happen.

#11

How do you see that the memory isn’t released? Did you check the count of the objects in Xojo? There is also a difference between the total memory and the used memory.

#12

There are three reasons which lead me to believe the memory isn’t being released:

  • In Instruments, when I select the “Activity Monitor”, the value in column “Memory” for my app increases every time I open the view and doesn’t decrease when I close it.
  • Same for the column “Persistent” under “Allocations” in Instruments (see screenshot in my first post). The two values from the “Activity Monitor” and “Allocations” are identical.
  • I can force a LowMemory warning when I open and close the view often enough. I am not doing anything else in the app and it takes quite some “open and close” of the view but eventually the LowMemory warning will come up.