🚰 Menu component listener leak #761
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I think I found the leak. We are adding a listener to animate when hidden, but they are never removed. Therefore when it is opened repeatedly, the same events keep getting added again and again. |
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That’s one pretty issue you got there! Thank you very much for the in-depth analysis. Is either of you working on a PR already? |
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I'm not working on a PR for this, much lower priority than my card goof that is very problematic for alignment. Go for fixing it if you want. (Yea, he has been doing loads of good reviews like this for TodoMVC stuff.) |
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⭐ Thanks again, @samccone! |
samccone
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Dec 9, 2015
The initial leak found here #761 And then patched here 957656d Was never the "correct" fix. Yes the patch in 957656d cause us to no longer leak however we were still paying the cost of registering and unregistering for the same event over and over, as well as allocating a new bound scope each time (thus generating more garbage and thus eventually causing more time to be spent int GC) Instead I opted here to take advantage of addEventListener and its ability to automatically discard duplicate listeners. > If multiple identical EventListeners are registered on the same > EventTarget with the same parameters, the duplicate instances are > discarded. They do not cause the EventListener to be called twice, and > they do not need to be removed manually with the removeEventListener > method. https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#Multiple_identical_event_listeners Because there is no outside pointers into this event, there is no need to remove the listener anymore, because once the node reference becomes unreachable the events will be automatically GCd for us. :)
TheOnlyMerlin
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May 20, 2017
The initial leak found here google/material-design-lite#761 And then patched here google/material-design-lite@957656d Was never the "correct" fix. Yes the patch in 957656d2beaab2d990b7758c8f13f44f9d0dfaf3 cause us to no longer leak however we were still paying the cost of registering and unregistering for the same event over and over, as well as allocating a new bound scope each time (thus generating more garbage and thus eventually causing more time to be spent int GC) Instead I opted here to take advantage of addEventListener and its ability to automatically discard duplicate listeners. > If multiple identical EventListeners are registered on the same > EventTarget with the same parameters, the duplicate instances are > discarded. They do not cause the EventListener to be called twice, and > they do not need to be removed manually with the removeEventListener > method. https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener#Multiple_identical_event_listeners Because there is no outside pointers into this event, there is no need to remove the listener anymore, because once the node reference becomes unreachable the events will be automatically GCd for us. :)
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Hypothesis: The menu when opened and closed does not clean up all of the events that it registers for, thus causing a leak 💧 .
#### Testing methodology:*visit http://www.getmdl.io/components/index.html#menus-section in chrome canary in an incognito window with no profile
Results:
The profiler shows us a step ladder of listener registrations (that never drops), over 5 iterations we can see that there are 15 new event registrations.
Looking at the heap comparison
note how that 15 shows up for us :) it looks like here ☝️ is the manifestation of our leak 👏
I have not investigated the menu code in depth for how the menu works, so this might be super obvious to you guys for how to fix (or even that this might not be an issue), if this is not enough info to go off of let me know and I can continue the dive.
🌴
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