Bk/performance optimizations

Example/MagazineLayoutExample/PerformanceDemoViewController.swift

@@ -26,7 +26,7 @@ final class PerformanceDemoViewController: UIViewController {
   override func viewDidLoad() {
     super.viewDidLoad()
 
-    title = "Performance (10K Items)"
+    title = "Performance (100K Items)"
     view.backgroundColor = .systemBackground
 
     navigationItem.rightBarButtonItems = [
@@ -71,8 +71,8 @@ final class PerformanceDemoViewController: UIViewController {
   ]
 
   private func loadInitialData() {
-    // Create 10,000 items
-    items = (0..<10_000).map { index in
+    // Create 100,000 items
+    items = (0..<100_000).map { index in
       let color = colors[index % colors.count]
       let item = PerformanceItem(id: nextItemID, color: color)
       nextItemID += 1

Example/MagazineLayoutExample/RootMenuViewController.swift

@@ -198,7 +198,7 @@ private enum DemoOption: String, CaseIterable {
     case .messageThread:
       return "Bottom-to-top layout with pagination"
     case .performance:
-      return "10,000 items with traditional data source"
+      return "100,000 items with traditional data source"
     }
   }
 

MagazineLayout.podspec

@@ -8,8 +8,8 @@ Pod::Spec.new do |s|
   s.source   = { :git => 'https://github.com/airbnb/MagazineLayout.git', :tag => "v#{ s.version.to_s }" }
   s.swift_version = '4.0'
   s.source_files = 'MagazineLayout/**/*.{swift,h}'
-  s.ios.deployment_target = '10.0'
-  s.tvos.deployment_target = '10.0'
+  s.ios.deployment_target = '12.0'
+  s.tvos.deployment_target = '12.0'
 
   s.pod_target_xcconfig = {
     'APPLICATION_EXTENSION_API_ONLY' => 'YES'

MagazineLayout.xcodeproj/project.pbxproj

@@ -39,6 +39,7 @@
 		93A1C04E21ACED1100DED67D /* ElementLocationFramePairsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A1C00F21ACED0100DED67D /* ElementLocationFramePairsTests.swift */; };
 		93A1C04F21ACED1100DED67D /* ModelStateUpdateTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A1C01021ACED0100DED67D /* ModelStateUpdateTests.swift */; };
 		93A868552EE0D7870027691E /* IDGenerator.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93A868542EE0D7870027691E /* IDGenerator.swift */; };
+		93F8DAE62FD76026005325C0 /* Signposting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 93F8DAE52FD76026005325C0 /* Signposting.swift */; };
 		FCAC642622085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift in Sources */ = {isa = PBXBuildFile; fileRef = FCAC642522085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift */; };
 		FCAC642822085B0E00973F4C /* FooterModel.swift in Sources */ = {isa = PBXBuildFile; fileRef = FCAC642722085B0E00973F4C /* FooterModel.swift */; };
 		FD244FEF28B41F9900046C0D /* UITraitCollection+DisplayScale.swift in Sources */ = {isa = PBXBuildFile; fileRef = FD244FEE28B41F9900046C0D /* UITraitCollection+DisplayScale.swift */; };
@@ -96,6 +97,7 @@
 		93A1C05321ACEDFC00DED67D /* LICENSE */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text; path = LICENSE; sourceTree = SOURCE_ROOT; };
 		93A1C05421ACEDFC00DED67D /* README.md */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = net.daringfireball.markdown; path = README.md; sourceTree = SOURCE_ROOT; };
 		93A868542EE0D7870027691E /* IDGenerator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IDGenerator.swift; sourceTree = "<group>"; };
+		93F8DAE52FD76026005325C0 /* Signposting.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Signposting.swift; sourceTree = "<group>"; };
 		FCAC642522085AF100973F4C /* MagazineLayoutHeaderVisibilityMode.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = MagazineLayoutHeaderVisibilityMode.swift; sourceTree = "<group>"; };
 		FCAC642722085B0E00973F4C /* FooterModel.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FooterModel.swift; sourceTree = "<group>"; };
 		FD23F5F021AF4A1B00AA78D4 /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
@@ -221,6 +223,7 @@
 		93A1C01F21ACED0100DED67D /* Types */ = {
 			isa = PBXGroup;
 			children = (
+				93F8DAE52FD76026005325C0 /* Signposting.swift */,
 				93A1C02221ACED0100DED67D /* MagazineLayoutSectionMetrics.swift */,
 				93A1C02621ACED0100DED67D /* MagazineLayoutItemWidthMode+WidthDivisor.swift */,
 				93A1C02321ACED0100DED67D /* CollectionViewUpdateItem.swift */,
@@ -365,6 +368,7 @@
 				93A1C03521ACED0100DED67D /* MagazineLayoutBackgroundVisibilityMode.swift in Sources */,
 				93A1C04421ACED0100DED67D /* SectionModel.swift in Sources */,
 				93A1C03E21ACED0100DED67D /* ElementLocation.swift in Sources */,
+				93F8DAE62FD76026005325C0 /* Signposting.swift in Sources */,
 				93A1C04821ACED0100DED67D /* ModelState.swift in Sources */,
 				93A868552EE0D7870027691E /* IDGenerator.swift in Sources */,
 				9398462A2296864200E442DA /* RowOffsetTracker.swift in Sources */,
@@ -468,7 +472,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 10.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				MTL_ENABLE_DEBUG_INFO = INCLUDE_SOURCE;
 				MTL_FAST_MATH = YES;
 				ONLY_ACTIVE_ARCH = YES;
@@ -477,7 +481,7 @@
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2,3";
-				TVOS_DEPLOYMENT_TARGET = 10.0;
+				TVOS_DEPLOYMENT_TARGET = 12.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -530,15 +534,15 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 10.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 12.0;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				MTL_FAST_MATH = YES;
 				SUPPORTED_PLATFORMS = "iphonesimulator iphoneos appletvsimulator appletvos";
 				SWIFT_COMPILATION_MODE = wholemodule;
 				SWIFT_OPTIMIZATION_LEVEL = "-O";
 				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2,3";
-				TVOS_DEPLOYMENT_TARGET = 10.0;
+				TVOS_DEPLOYMENT_TARGET = 12.0;
 				VALIDATE_PRODUCT = YES;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";

MagazineLayout/LayoutCore/SectionModel.swift

@@ -38,7 +38,10 @@ struct SectionModel {
     numberOfRows = 0
 
     updateIndexOfFirstInvalidatedRowIfNecessary(toProposedIndex: 0)
-    calculateElementFramesIfNecessary()
+
+    if !MagazineLayout._enableExperimentalOptimizations {
+      calculateElementFramesIfNecessary()
+    }
   }
 
   // MARK: Internal
@@ -257,15 +260,22 @@ struct SectionModel {
   }
 
   mutating func removeFooter() -> Bool {
-    guard let indexOfFooter = indexOfFooterRow() else {
+    guard footerModel != nil else {
       return false
     }
-    updateIndexOfFirstInvalidatedRowIfNecessary(toProposedIndex: indexOfFooter)
+    // `indexOfFooterRow()` is `nil` if the section hasn't been laid out yet (deferred layout
+    // calculation). In that case the whole section is already invalidated from row 0, so there's no
+    // additional row to invalidate.
+    if let indexOfFooter = indexOfFooterRow() {
+      updateIndexOfFirstInvalidatedRowIfNecessary(toProposedIndex: indexOfFooter)
+    }
     footerModel = nil
     return true
   }
 
   mutating func updateItemHeight(toPreferredHeight preferredHeight: CGFloat, atIndex index: Int) {
+    calculateElementFramesIfNecessary()
+
     // Accessing this array using an unsafe, untyped (raw) pointer avoids expensive copy-on-writes
     // and Swift retain / release calls.
     itemModels.withUnsafeMutableBufferPointer { directlyMutableItemModels in
@@ -292,6 +302,8 @@ struct SectionModel {
   }
 
   mutating func updateHeaderHeight(toPreferredHeight preferredHeight: CGFloat) {
+    calculateElementFramesIfNecessary()
+
     headerModel?.preferredHeight = preferredHeight
 
     if let indexOfHeaderRow = indexOfHeaderRow(), let headerModel = headerModel {
@@ -312,6 +324,8 @@ struct SectionModel {
   }
 
   mutating func updateFooterHeight(toPreferredHeight preferredHeight: CGFloat) {
+    calculateElementFramesIfNecessary()
+
     footerModel?.preferredHeight = preferredHeight
 
     if let indexOfFooterRow = indexOfFooterRow(), let footerModel = footerModel {
@@ -393,7 +407,10 @@ struct SectionModel {
   }
 
   private func indexOfFooterRow() -> Int? {
-    guard footerModel != nil else { return nil }
+    // `numberOfRows` is 0 until the section's element frames have been calculated. With deferred
+    // layout calculation, the footer's row index isn't known yet in that state, so we return `nil`
+    // rather than a bogus `numberOfRows - 1` (which would be -1).
+    guard footerModel != nil, numberOfRows > 0 else { return nil }
     return numberOfRows - 1
   }
 

MagazineLayout/LayoutCore/Types/Signposting.swift

@@ -0,0 +1,33 @@
+// Created by Bryan Keller on 6/8/26.
+// Copyright © 2026 Airbnb Inc. All rights reserved.
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import os
+
+// MARK: - Signposting
+
+let signpostLog = OSLog(subsystem: "com.airbnb.MagazineLayout", category: "MagazineLayout")
+
+enum SignpostName {
+  static let collectionViewContentSize: StaticString = "MagazineLayout.collectionViewContentSize"
+  static let prepare: StaticString = "MagazineLayout.prepare"
+  static let prepareUpdateWidths: StaticString = "MagazineLayout.prepare.prepareUpdateWidths"
+  static let prepareUpdateLayoutMetrics: StaticString = "MagazineLayout.prepare.prepareUpdateLayoutMetrics"
+  static let prepareRecreateSectionModels: StaticString = "MagazineLayout.prepare.recreateSectionModels"
+  static let layoutAttributesForElementsInRect: StaticString = "MagazineLayout.layoutAttributesForElementsInRect"
+  static let prepareForCollectionViewUpdates: StaticString = "MagazineLayout.prepareForCollectionViewUpdates"
+  static let invalidateLayout: StaticString = "MagazineLayout.invalidateLayout"
+  static let preferredLayoutAttributesFittingCell: StaticString = "MagazineLayout.preferredLayoutAttributesFitting.cell"
+  static let preferredLayoutAttributesFittingReusableView: StaticString = "MagazineLayout.preferredLayoutAttributesFitting.reusableView"
+}