Bk/performance optimizations 2#159
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bryankeller
commented
Jun 9, 2026
Comment on lines
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| private func mutateSectionModels( | ||
| withUnsafeMutableBufferPointer body: (inout UnsafeMutableBufferPointer<SectionModel>) -> Void) | ||
| { | ||
| // Accessing these arrays using unsafe, untyped (raw) pointers | ||
| // avoids expensive copy-on-writes and Swift retain / release calls. | ||
| sectionModels.withUnsafeMutableBufferPointer(body) | ||
| } |
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no reason for this helper
bryankeller
commented
Jun 9, 2026
Comment on lines
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| if MagazineLayout._enableExperimentalOptimizations { | ||
| sectionModels.withUnsafeMutableBufferPointer { sectionModels in | ||
| for (itemModel, insertIndexPath) in (itemModelInsertIndexPathPairs.sorted { $0.insertIndexPath < $1.insertIndexPath }) { | ||
| let sectionIndex = insertIndexPath.section | ||
| let itemIndex = insertIndexPath.item | ||
| let section = sectionModels[sectionIndex] | ||
| if itemIndex < section.numberOfItems, itemModel.id == section.idForItemModel(atIndex: itemIndex) { | ||
| // If the `itemModel` to insert already exists at the destination index, then there's no need to insert it again. This | ||
| // happens if item move updates are generated in addition to section move updates, which appears to be the case when using | ||
| // `UICollectionViewDiffableDataSource`. Other diffing approaches, like Paul Heckel's, do not produce item moves when | ||
| // their containing sections move. | ||
| continue | ||
| } else { | ||
| sectionModels[insertIndexPath.section].insert(itemModel, atIndex: itemIndex) | ||
| } | ||
| } | ||
| } | ||
| } else { | ||
| for (itemModel, insertIndexPath) in (itemModelInsertIndexPathPairs.sorted { $0.insertIndexPath < $1.insertIndexPath }) { | ||
| let sectionIndex = insertIndexPath.section | ||
| let itemIndex = insertIndexPath.item | ||
| let section = sectionModels[sectionIndex] | ||
| if itemIndex < section.numberOfItems, itemModel.id == section.idForItemModel(atIndex: itemIndex) { | ||
| // If the `itemModel` to insert already exists at the destination index, then there's no need to insert it again. This | ||
| // happens if item move updates are generated in addition to section move updates, which appears to be the case when using | ||
| // `UICollectionViewDiffableDataSource`. Other diffing approaches, like Paul Heckel's, do not produce item moves when | ||
| // their containing sections move. | ||
| continue | ||
| } else { | ||
| sectionModels[insertIndexPath.section].insert(itemModel, atIndex: itemIndex) | ||
| } |
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nothing new here, just copy and pasted into two branches so we can safely test
bryankeller
commented
Jun 9, 2026
| } | ||
|
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||
| let numberOfItems = modelState.numberOfItems(inSectionAtIndex: sectionIndex) | ||
| for itemIndex in 0..<numberOfItems { |
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this diff is kind of annoying - this else branch is just the existing code but indented.
bryankeller
commented
Jun 9, 2026
Comment on lines
+123
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| modelState.forEachSectionModel { sectionIndex, sectionModel in | ||
| reusableIndexPath.section = sectionIndex | ||
| } | ||
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| let sectionMetrics = metricsForSection(atIndex: sectionIndex) | ||
| modelState.updateMetrics(to: sectionMetrics, forSectionAtIndex: sectionIndex) | ||
| modelState.updateMetrics( | ||
| to: metricsForSection(atIndex: sectionIndex), | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
|
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| if let headerModel = headerModelForHeader(inSectionAtIndex: sectionIndex) { | ||
| modelState.setHeader(headerModel, forSectionAtIndex: sectionIndex) | ||
| } else { | ||
| modelState.removeHeader(forSectionAtIndex: sectionIndex) | ||
| } | ||
| if let headerModel = headerModelForHeader(inSectionAtIndex: sectionIndex) { | ||
| modelState.setHeader( | ||
| headerModel, | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
| } else { | ||
| modelState.removeHeader(forSectionAtIndex: sectionIndex, sectionModel: §ionModel) | ||
| } | ||
|
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| if let footerModel = footerModelForFooter(inSectionAtIndex: sectionIndex) { | ||
| modelState.setFooter(footerModel, forSectionAtIndex: sectionIndex) | ||
| } else { | ||
| modelState.removeFooter(forSectionAtIndex: sectionIndex) | ||
| } | ||
| if let footerModel = footerModelForFooter(inSectionAtIndex: sectionIndex) { | ||
| modelState.setFooter( | ||
| footerModel, | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
| } else { | ||
| modelState.removeFooter(forSectionAtIndex: sectionIndex, sectionModel: §ionModel) | ||
| } | ||
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| if let backgroundModel = backgroundModelForBackground(inSectionAtIndex: sectionIndex) { | ||
| modelState.setBackground(backgroundModel, forSectionAtIndex: sectionIndex) | ||
| } else { | ||
| modelState.removeBackground(forSectionAtIndex: sectionIndex) | ||
| } | ||
| if let backgroundModel = backgroundModelForBackground(inSectionAtIndex: sectionIndex) { | ||
| modelState.setBackground( | ||
| backgroundModel, | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
| } else { | ||
| modelState.removeBackground( | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
| } | ||
|
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| let numberOfItems = modelState.numberOfItems(inSectionAtIndex: sectionIndex) | ||
| for itemIndex in 0..<numberOfItems { | ||
| if Self._enableExperimentalOptimizations { | ||
| modelState.updateItemSizeModes( | ||
| forSectionAtIndex: sectionIndex, | ||
| sectionModel: §ionModel) | ||
| { itemIndex in | ||
| reusableIndexPath.item = itemIndex | ||
| modelState.updateItemSizeMode(to: sizeModeForItem(at: reusableIndexPath), forItemAt: reusableIndexPath) | ||
| return sizeModeForItem(at: reusableIndexPath) | ||
| } |
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this is the same code as the else branch, but using the batch-mutators - shaves ~10ms off of this work for 100k items.
brynbodayle
approved these changes
Jun 9, 2026
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Details
Reduce some array overhead by using
UnsafeMutableBufferPointerwhen batch-updating thesectionModelsanditemModelsarrays.How Has This Been Tested
Tested in demo app and Airbnb app. Additionally, all unit tests pass.
Types of changes