[Bug] Closing multiple tabs is slow if animation is disabled

[valadaptive]

[Bug] Closing multiple tabs is slow if animation is disabled

[irvinm]

@piroor, I just wanted to make sure you saw this one. Still has the "needs-triage" tag.

[piroor]

Thank you for detailed investigation! I agree that the current mechanism can trigger too many function calls to update tree indentation. Such needless calls needs to be reduced.

My concern about the PR #3384 is: it will introduce a regression around some situations like tree collapsion/expansion. With the present version, you'll see shallowly indented tree without delay when you expand a deeply nested tree. But with the change you proposed, you'll see "very deeply indented tree" at first and it will be updated to "shallowly indented tree" with a delay. (TST automatically adjusts indent width of tree based on currently visible tree at all time.) I'm afraid that such a visual flicking may stress people suffered from an epileptic seizure - we need to remind that the disabled animation mode is used by no only performance oriented people but handicapped people also.

Anyway the performance issue you mentioned is really serious with large number tabs. As a compromise, I've introduced a change. The main idea is based on your PR but there is a difference: the delayed update is activated only when the function is called over 10 times at a time. I hope the change helps you.

[piroor]

After more experiments, now TST updates max indent of collapsed/expanded tree with less function call and without delay. Of course the threshold mechanism is also still available and it should be effective for other cases like reported here - it is mostly equivalent to your PR. Thanks to mention about this performance issue I missed!