mirror of
https://github.com/Instagram/IGListKit
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ba2b3150b0
Summary: ## Context Merging multiple batch updates of the same section is inherently unsafe, because each block can mutate the underlaying list and lead to insert/deletes that operate on different before/after lists. The long term fix is to get rid of item level batch updates (insert/delete calls) and use diffing like for sections, but that's a much larger project. Right now, we have a crash spiking because we're reloading the same cell multiple times. Each time `IGListDiff(...)` returns a pair of insert/delete for the same index (lets say 0). Once these updates are merge together, they look like this: ``` Item inserts = 0, 0 Item deletes = 0, 0 ``` We dedupe deletes in `IGListBatchUpdateData`, but don't do anything for inserts, so it looks liket this: ``` Item inserts = 0, 0 Item deletes = 0 ``` So we create an insert/delete unbalance and can crash. Tbh, not sure how this hasn't been a bigger issue in the past. D21822502 tried to remove all duplicate inserts, but that caused other types of crashes, because multiple inserts are allowed. ## This diff * Lets keep the net insert/delete count the same by keeping track of the number of deletes we remove and apply the same to inserts. * Add some tests * Add an experiment flag to kill this if needed to be safe. IG only: Note that I'm making the default true because the crash is happening pretty at start-up. ## Follow up Over time, the batch update clean up logic was slowly added to multiple place (IGListBatchUpdateData, IGListAdapterUpdaterHelpers, IGListIndexPathResult), which is making it hard to follow. A first step would be to move it in 1 or 2 places and avoid redundant logic (like getting unique deletes). However, the real fix is getting rid of batch updates all together. Differential Revision: D61719884 fbshipit-source-id: eda7c264c8239a6a106dbe0256fe777b38fae335 |
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|---|---|---|
| .. | ||
| Internal | ||
| IGListAssert.h | ||
| IGListBatchUpdateData.h | ||
| IGListBatchUpdateData.mm | ||
| IGListCompatibility.h | ||
| IGListDiff.h | ||
| IGListDiff.mm | ||
| IGListDiffable.h | ||
| IGListDiffKit.h | ||
| IGListExperiments.h | ||
| IGListIndexPathResult.h | ||
| IGListIndexPathResult.m | ||
| IGListIndexSetResult.h | ||
| IGListIndexSetResult.m | ||
| IGListMacros.h | ||
| IGListMoveIndex.h | ||
| IGListMoveIndex.m | ||
| IGListMoveIndexPath.h | ||
| IGListMoveIndexPath.m | ||
| NSNumber+IGListDiffable.h | ||
| NSNumber+IGListDiffable.m | ||
| NSString+IGListDiffable.h | ||
| NSString+IGListDiffable.m | ||