PostThread perf: reduce time wasted on rendering skeletons (#10092)

src/screens/PostThread/components/ThreadItemAnchor.tsx

@@ -1,4 +1,4 @@
-import {memo, useCallback, useMemo} from 'react'
+import {memo, useMemo} from 'react'
 import {Text as RNText, View} from 'react-native'
 import {
   AppBskyFeedDefs,
@@ -9,6 +9,7 @@ import {
 } from '@atproto/api'
 import {Plural, Trans, useLingui} from '@lingui/react/macro'
 
+import {useNonReactiveCallback} from '#/lib/hooks/useNonReactiveCallback'
 import {useOpenComposer} from '#/lib/hooks/useOpenComposer'
 import {makeProfileLink} from '#/lib/routes/links'
 import {sanitizeDisplayName} from '#/lib/strings/display-names'
@@ -245,7 +246,7 @@ const ThreadItemAnchorInner = memo(function ThreadItemAnchorInner({
     }
   }, [postSource])
 
-  const onPressReply = useCallback(() => {
+  const onPressReply = useNonReactiveCallback(() => {
     openComposer({
       replyTo: {
         uri: post.uri,
@@ -268,15 +269,7 @@ const ThreadItemAnchorInner = memo(function ThreadItemAnchorInner({
         reqId: postSource.post.reqId,
       })
     }
-  }, [
+  })
-    openComposer,
-    post,
-    record,
-    onPostSuccess,
-    moderation,
-    postSource,
-    feedFeedback,
-  ])
 
   const onOpenAuthor = () => {
     ax.metric('post:clickthroughAuthor', {

src/screens/PostThread/index.tsx

@@ -1,9 +1,17 @@
-import {useCallback, useEffect, useMemo, useRef, useState} from 'react'
+import {
+  startTransition,
+  useCallback,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+} from 'react'
 import {useWindowDimensions, View} from 'react-native'
 import Animated, {useAnimatedStyle} from 'react-native-reanimated'
 import {Trans} from '@lingui/react/macro'
 
 import {useInitialNumToRender} from '#/lib/hooks/useInitialNumToRender'
+import {useNonReactiveCallback} from '#/lib/hooks/useNonReactiveCallback'
 import {useOpenComposer} from '#/lib/hooks/useOpenComposer'
 import {usePostViewTracking} from '#/lib/hooks/usePostViewTracking'
 import {useFeedFeedback} from '#/state/feed-feedback'
@@ -98,7 +106,7 @@ export function PostThread({uri}: {uri: string}) {
   const trackThreadItemView = usePostViewTracking('PostThreadItem')
 
   const {openComposer} = useOpenComposer()
-  const optimisticOnPostReply = useCallback(
+  const optimisticOnPostReply = useNonReactiveCallback(
     (payload: OnPostSuccessData) => {
       if (payload) {
         const {replyToUri, posts} = payload
@@ -107,9 +115,8 @@ export function PostThread({uri}: {uri: string}) {
         }
       }
     },
-    [thread],
   )
-  const onReplyToAnchor = useCallback(() => {
+  const onReplyToAnchor = useNonReactiveCallback(() => {
     if (anchor?.type !== 'threadPost') {
       return
     }
@@ -136,13 +143,7 @@ export function PostThread({uri}: {uri: string}) {
         reqId: anchorPostSource.post.reqId,
       })
     }
-  }, [
+  })
-    anchor,
-    openComposer,
-    optimisticOnPostReply,
-    anchorPostSource,
-    feedFeedback,
-  ])
 
   const isRoot = !!anchor && anchor.value.post.record.reply === undefined
   const canReply = !anchor?.value.post?.viewer?.replyDisabled
@@ -389,12 +390,34 @@ export function PostThread({uri}: {uri: string}) {
     return results
   }, [thread, deferParents, maxParentCount, maxChildrenCount])
 
+  /**
+   * Defer rendering reply skeletons so that the anchor post (from cache)
+   * can paint without being blocked by skeleton layout work. On mount,
+   * skeletons are filtered out. After the first render, they're added
+   * back via a low-priority transition.
+   */
+  const [showReplySkeletons, setShowReplySkeletons] = useState(false)
+  useEffect(() => {
+    if (thread.state.isPlaceholderData && !showReplySkeletons) {
+      startTransition(() => {
+        setShowReplySkeletons(true)
+      })
+    }
+  }, [thread.state.isPlaceholderData, showReplySkeletons])
+
+  const deferredSlices = useMemo(() => {
+    if (showReplySkeletons) return slices
+    return slices.filter(
+      item => !(item.type === 'skeleton' && item.item === 'reply'),
+    )
+  }, [slices, showReplySkeletons])
+
   const isTombstoneView = useMemo(() => {
-    if (slices.length > 1) return false
+    if (deferredSlices.length > 1) return false
-    return slices.every(
+    return deferredSlices.every(
       s => s.type === 'threadPostBlocked' || s.type === 'threadPostNotFound',
     )
-  }, [slices])
+  }, [deferredSlices])
 
   const renderItem = useCallback(
     ({item, index}: {item: ThreadItem; index: number}) => {
@@ -547,7 +570,7 @@ export function PostThread({uri}: {uri: string}) {
       ) : (
         <List
           ref={listRef}
-          data={slices}
+          data={deferredSlices}
           renderItem={renderItem}
           keyExtractor={keyExtractor}
           onContentSizeChange={platform({
@@ -594,8 +617,10 @@ export function PostThread({uri}: {uri: string}) {
           initialNumToRender={initialNumToRender}
           /**
            * Default: 21
+           *
+           * Smaller for placeholder data so we don't waste time rendering skeletons
            */
-          windowSize={7}
+          windowSize={thread.state.isPlaceholderData ? 1 : 7}
           /**
            * Default: 10
            */