improve performance of Differ.diffContentMultiple by ~ 100x for lar…

…ge lists of views.

Co-authored-by: Mathias Brandewinder <mathias@brandewinder.com>
Co-authored-by: Richard Webb <richard.webb@helpsystems.com>

src/Avalonia.FuncUI.Benchmarks/Scenarios/Diffing/GameOfLife.fs

@@ -1,14 +1,16 @@
 namespace Avalonia.FuncUI.Benchmarks.Scenarios.Diffing
 
 open System
+
 open Avalonia.Controls
 open Avalonia.Controls.Primitives
 open Avalonia.FuncUI.DSL
-
 open Avalonia.FuncUI.Types
 open Avalonia.Layout
 open Avalonia.Media
+
 open BenchmarkDotNet.Attributes
+open BenchmarkDotNet.Engines
 
 [<RequireQualifiedAccess>]
 module GameOfLife =
@@ -48,7 +50,6 @@ module GameOfLife =
             ]
         ]
 
-
 open Avalonia.FuncUI.VirtualDom.Delta
 
 module internal rec DifferChampionA =
@@ -201,6 +202,315 @@ module internal rec DifferChampionA =
               KeyDidChange = false
               Outlet = next.Outlet }
 
+module internal rec DifferChampionB =
+
+    let private update (last: IAttr, next: IAttr) : AttrDelta =
+        match next with
+        | Property' property ->
+            AttrDelta.Property
+                { Accessor = property.Accessor
+                  Value = Some property.Value
+                  DefaultValueFactory = property.DefaultValueFactory }
+
+        | Content' content ->
+            AttrDelta.Content
+                { Accessor = content.Accessor;
+                  Content = diffContent (last, next) }
+
+        | Subscription' subscription ->
+            AttrDelta.Subscription (SubscriptionDelta.From subscription)
+
+        | InitFunction init ->
+            AttrDelta.SetupFunction init
+
+        | _ -> failwithf "no update operation is defined for '%A' next" next
+
+    let private reset (last: IAttr) : AttrDelta =
+        match last with
+        | Property' property ->
+            AttrDelta.Property
+                { Accessor = property.Accessor;
+                  Value = None
+                  DefaultValueFactory = property.DefaultValueFactory }
+
+        | Content' content ->
+            let empty =
+                match content.Content with
+                | ViewContent.Single _ -> ViewContentDelta.Single None
+                | ViewContent.Multiple _ -> ViewContentDelta.Multiple []
+
+            AttrDelta.Content
+                { Accessor = content.Accessor;
+                  Content = empty }
+
+        | Subscription' subscription ->
+            AttrDelta.Subscription
+                { Name = subscription.Name
+                  Subscribe = subscription.Subscribe
+                  Func = None }
+
+        | InitFunction init ->
+            AttrDelta.SetupFunction init
+
+        | _ -> failwithf "no reset operation is defined for last '%A'" last
+
+    let private diffContentSingle (last: IView option, next: IView option) : ViewDelta option =
+        match next with
+        | Some next ->
+            match last with
+            | Some last -> Some (diff(last, next))
+            | None -> Some (ViewDelta.From next)
+        | None -> None
+
+    let private diffContentMultiple (lastList: IView list, nextList: IView list) : ViewDelta list =
+        let lastListLength = lastList.Length
+
+        let mutable lastTail: IView list = lastList
+
+        nextList |> List.mapi (fun index next ->
+            if index + 1 <= lastListLength then
+                let result = diff(lastTail.Head, next)
+                lastTail <- lastTail.Tail
+                result
+            else
+                ViewDelta.From next
+        )
+
+    let private diffContent (last: IAttr, next: IAttr) : ViewContentDelta =
+            match next with
+            | Content' nextContent ->
+                match last with
+                | Content' lastContent ->
+                    match nextContent.Content with
+
+                    // Single Content
+                    | ViewContent.Single nextSingleContent ->
+                        match lastContent.Content with
+                        | ViewContent.Single lastSingleContent ->
+                            ViewContentDelta.Single (diffContentSingle (lastSingleContent, nextSingleContent))
+                        | _ ->
+                            ViewContentDelta.Single None
+
+                    // Multiple Content
+                    | ViewContent.Multiple nextMultipleContent ->
+                        match lastContent.Content with
+                        | ViewContent.Multiple lastMultipleContent ->
+                            ViewContentDelta.Multiple (diffContentMultiple (lastMultipleContent, nextMultipleContent))
+                        | _ ->
+                            ViewContentDelta.Multiple (diffContentMultiple (List.empty, nextMultipleContent))
+
+                | _ -> invalidOp "'last' must be of type content"
+
+            | _ -> invalidOp "'next' must be of type content"
+
+    let internal diffAttributes (lastAttrs: IAttr list, nextAttrs: IAttr list) : AttrDelta list =
+
+        let delta = ResizeArray<AttrDelta>()
+
+        (* check if there is a corresponding new attribute for all old attributes *)
+        for lastAttr in lastAttrs do
+
+            let isAttrStillPresent =
+                nextAttrs
+                |> List.tryFind (fun nextAttr -> nextAttr.UniqueName = lastAttr.UniqueName)
+
+            (* check if attribute is still present *)
+            match isAttrStillPresent with
+
+            (* attribute is still there, but it's value changed. -> update value *)
+            | Some nextAttr when not (nextAttr.Equals lastAttr) ->
+                let attrDelta = update (lastAttr, nextAttr)
+                delta.Add attrDelta
+
+            (* attribute is still there. It hasn't changed -> do nothing *)
+            | Some _ -> ()
+
+            (* attribute is no longer present. -> reset value *)
+            | None ->
+                let attrDelta = reset lastAttr
+                delta.Add attrDelta
+
+        (* check if new attributes need to be added  *)
+        for nextAttr in nextAttrs do
+
+            let attrIsAlreadyKnown =
+                lastAttrs
+                |> List.exists (fun lastAttr -> lastAttr.UniqueName = nextAttr.UniqueName)
+
+            (* attribute is new - create delta from it -> set value  *)
+            if not attrIsAlreadyKnown then
+                delta.Add (AttrDelta.From nextAttr)
+
+        List.ofSeq delta
+
+    let diff (last: IView, next: IView) : ViewDelta =
+        // only diff attributes if viewType/viewKey matches
+        if last.ViewKey <> next.ViewKey then
+            ViewDelta.From (next, true)
+        elif last.ViewType <> next.ViewType then
+            ViewDelta.From next
+        else
+            { ViewType = next.ViewType
+              Attrs = diffAttributes (last.Attrs, next.Attrs)
+              ConstructorArgs = next.ConstructorArgs
+              KeyDidChange = false
+              Outlet = next.Outlet }
+
+module internal rec DifferChampionC =
+
+    let private update (last: IAttr, next: IAttr) : AttrDelta =
+        match next with
+        | Property' property ->
+            AttrDelta.Property
+                { Accessor = property.Accessor
+                  Value = Some property.Value
+                  DefaultValueFactory = property.DefaultValueFactory }
+
+        | Content' content ->
+            AttrDelta.Content
+                { Accessor = content.Accessor;
+                  Content = diffContent (last, next) }
+
+        | Subscription' subscription ->
+            AttrDelta.Subscription (SubscriptionDelta.From subscription)
+
+        | InitFunction init ->
+            AttrDelta.SetupFunction init
+
+        | _ -> failwithf "no update operation is defined for '%A' next" next
+
+    let private reset (last: IAttr) : AttrDelta =
+        match last with
+        | Property' property ->
+            AttrDelta.Property
+                { Accessor = property.Accessor;
+                  Value = None
+                  DefaultValueFactory = property.DefaultValueFactory }
+
+        | Content' content ->
+            let empty =
+                match content.Content with
+                | ViewContent.Single _ -> ViewContentDelta.Single None
+                | ViewContent.Multiple _ -> ViewContentDelta.Multiple []
+
+            AttrDelta.Content
+                { Accessor = content.Accessor;
+                  Content = empty }
+
+        | Subscription' subscription ->
+            AttrDelta.Subscription
+                { Name = subscription.Name
+                  Subscribe = subscription.Subscribe
+                  Func = None }
+
+        | InitFunction init ->
+            AttrDelta.SetupFunction init
+
+        | _ -> failwithf "no reset operation is defined for last '%A'" last
+
+    let private diffContentSingle (last: IView option, next: IView option) : ViewDelta option =
+        match next with
+        | Some next ->
+            match last with
+            | Some last -> Some (diff(last, next))
+            | None -> Some (ViewDelta.From next)
+        | None -> None
+
+    let private diffContentMultiple (lastList: IView list, nextList: IView list) : ViewDelta list =
+        let lastListLength = lastList.Length
+
+        let mutable lastTail: IView list = lastList
+
+        nextList |> List.mapi (fun index next ->
+            if index < lastListLength then
+                let result = diff(lastTail.Head, next)
+                lastTail <- lastTail.Tail
+                result
+            else
+                ViewDelta.From next
+        )
+
+    let private diffContent (last: IAttr, next: IAttr) : ViewContentDelta =
+            match next with
+            | Content' nextContent ->
+                match last with
+                | Content' lastContent ->
+                    match nextContent.Content with
+
+                    // Single Content
+                    | ViewContent.Single nextSingleContent ->
+                        match lastContent.Content with
+                        | ViewContent.Single lastSingleContent ->
+                            ViewContentDelta.Single (diffContentSingle (lastSingleContent, nextSingleContent))
+                        | _ ->
+                            ViewContentDelta.Single None
+
+                    // Multiple Content
+                    | ViewContent.Multiple nextMultipleContent ->
+                        match lastContent.Content with
+                        | ViewContent.Multiple lastMultipleContent ->
+                            ViewContentDelta.Multiple (diffContentMultiple (lastMultipleContent, nextMultipleContent))
+                        | _ ->
+                            ViewContentDelta.Multiple (diffContentMultiple (List.empty, nextMultipleContent))
+
+                | _ -> invalidOp "'last' must be of type content"
+
+            | _ -> invalidOp "'next' must be of type content"
+
+    let internal diffAttributes (lastAttrs: IAttr list, nextAttrs: IAttr list) : AttrDelta list =
+
+        let delta = ResizeArray<AttrDelta>()
+
+        (* check if there is a corresponding new attribute for all old attributes *)
+        for lastAttr in lastAttrs do
+
+            let isAttrStillPresent =
+                nextAttrs
+                |> List.tryFind (fun nextAttr -> nextAttr.UniqueName = lastAttr.UniqueName)
+
+            (* check if attribute is still present *)
+            match isAttrStillPresent with
+
+            (* attribute is still there, but it's value changed. -> update value *)
+            | Some nextAttr when not (nextAttr.Equals lastAttr) ->
+                let attrDelta = update (lastAttr, nextAttr)
+                delta.Add attrDelta
+
+            (* attribute is still there. It hasn't changed -> do nothing *)
+            | Some _ -> ()
+
+            (* attribute is no longer present. -> reset value *)
+            | None ->
+                let attrDelta = reset lastAttr
+                delta.Add attrDelta
+
+        (* check if new attributes need to be added  *)
+        for nextAttr in nextAttrs do
+
+            let attrIsAlreadyKnown =
+                lastAttrs
+                |> List.exists (fun lastAttr -> lastAttr.UniqueName = nextAttr.UniqueName)
+
+            (* attribute is new - create delta from it -> set value  *)
+            if not attrIsAlreadyKnown then
+                delta.Add (AttrDelta.From nextAttr)
+
+        List.ofSeq delta
+
+    let diff (last: IView, next: IView) : ViewDelta =
+        // only diff attributes if viewType/viewKey matches
+        if last.ViewKey <> next.ViewKey then
+            ViewDelta.From (next, true)
+        elif last.ViewType <> next.ViewType then
+            ViewDelta.From next
+        else
+            { ViewType = next.ViewType
+              Attrs = diffAttributes (last.Attrs, next.Attrs)
+              ConstructorArgs = next.ConstructorArgs
+              KeyDidChange = false
+              Outlet = next.Outlet }
+
+[<SimpleJob(RunStrategy.Throughput, warmupCount = 5, iterationCount = 5)>]
 [<MemoryDiagnoser; >]
 type GameOfLifeBench () =
 
@@ -228,3 +538,13 @@ type GameOfLifeBench () =
     member this.ChampionA () : unit =
         let _ = DifferChampionA.diff (viewLast.Value, viewNext.Value)
         ()
+
+    [<Benchmark>]
+    member this.ChampionB () : unit =
+        let _ = DifferChampionB.diff (viewLast.Value, viewNext.Value)
+        ()
+
+    [<Benchmark>]
+    member this.ChampionC () : unit =
+        let _ = DifferChampionC.diff (viewLast.Value, viewNext.Value)
+        ()

src/Avalonia.FuncUI/VirtualDom/VirtualDom.Differ.fs

@@ -64,9 +64,18 @@ module internal rec Differ =
         | None -> None
 
     let private diffContentMultiple (lastList: IView list, nextList: IView list) : ViewDelta list =
+        let lastListLength = lastList.Length
+
+        (* implementation that avoids indexed access to lists *)
+        (* more details: https://github.com/fsprojects/Avalonia.FuncUI/pull/317 *)
+
+        let mutable lastTail: IView list = lastList
+
         nextList |> List.mapi (fun index next ->
-            if index + 1 <= lastList.Length then
-                Differ.diff(lastList.[index], nextList.[index])
+            if index < lastListLength then
+                let result = diff(lastTail.Head, next)
+                lastTail <- lastTail.Tail
+                result
             else
                 ViewDelta.From next
         )