Bugfix FXIOS-10482 Improve memory usage during tab tray open/close

[mattreaganmozilla]

📜 Tickets

Jira ticket
Github issue

💡 Description

Bandaid for a memory leak that occurs after opening/closing the tab tray. A general memory comparison graph (before/after) is shown below.

The underlying bug is still a problem unfortunately, and I believe we are still leaking a few of the container views higher up in the view hierarchy. Additionally, I'm seeing some other related scenarios that need further investigation and also might be leaking other UI.

This PR, however, does free up memory use considerably in this basic scenario, so I'm opening this for review now so we can have this available in the meantime until there is a better longterm solution in place.

Note: this appears to be a longstanding issue with the tab tray that predates any of the recent UI updates.

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Memory Use Comparison

For this test the app was launched and then the tab tray was opened and closed repeatedly.

Allocations on device (iPhone 12 mini)

Before

After

Before

After

📝 Checklist

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• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
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[PARAIPAN9]

Definitely an improvement, @mattreaganmozilla. I see now an approximate 1MB increase in memory compared to 7MB previously, so an approximate of 7 times improvement. Really nice job.

[mattreaganmozilla]

I see now an approximate 1MB increase in memory compared to 7MB previously

@PARAIPAN9 What steps were you using to test? I'm still investigating so I'll take a closer look; 1MB is still a big memory leak and I'm actually not seeing that with the fix in place.

[PARAIPAN9]

@mattreaganmozilla, the same steps: Opening and closing the tab tray.

[mattreaganmozilla]

the same steps: Opening and closing the tab tray.

Ok interesting. For reference, I'm profiling on device (iPhone 12 mini) and if open/close the tray 10x these are the results I currently get:

Before

After

So this is just an approximation based on the output from Allocations, but across 10x repetitions I see about a ~1.2MB total increase in memory (or ~122kb each open/close) with the fix in place. Without the fix it's closer to ~25-30MB total (or about 2-3MB each open/close). So that's a factor of 20x or more.

In any case, I'd like to get the leak to zero so I'm going to keep this open a bit longer.