Multi-instance <TimeToInitialDisplay> / <TimeToFullDisplay> coordination; a multi-signal TTID/TTFD system

CHANGELOG.md

@@ -8,6 +8,13 @@
 
 ## Unreleased
 
+### Features
+
+- Multi-instance `<TimeToInitialDisplay>` / `<TimeToFullDisplay>` coordination ([#6090](https://github.com/getsentry/sentry-react-native/pull/6090)
+  - When a screen has multiple async data sources, you can now mount one `<TimeToFullDisplay>` per source — the TTID/TTFD will get recorded
+    only when all the sources report `ready`.   
+  - The new `ready` prop is declarative and replaces the previously imperative `record` prop, which is now marked as deprecated.
+
 ### Fixes
 
 - Fix the issue with uploading iOS Debug Symbols in EAS Build when using pnpm ([#6076](https://github.com/getsentry/sentry-react-native/issues/6076))

packages/core/src/js/tracing/timeToDisplayCoordinator.ts

@@ -0,0 +1,139 @@
+/**
+ * Coordinator for multi-instance `<TimeToInitialDisplay>` / `<TimeToFullDisplay>`
+ * components on a single screen (active span).
+ */
+
+type Checkpoint = { ready: boolean };
+type Listener = () => void;
+
+interface SpanRegistry {
+  checkpoints: Map<string, Checkpoint>;
+  listeners: Set<Listener>;
+}
+
+const TTID = 'ttid';
+const TTFD = 'ttfd';
+
+export type DisplayKind = typeof TTID | typeof TTFD;
+
+const registries: Record<DisplayKind, Map<string, SpanRegistry>> = {
+  ttid: new Map(),
+  ttfd: new Map(),
+};
+
+function getOrCreate(kind: DisplayKind, parentSpanId: string): SpanRegistry {
+  const map = registries[kind];
+  let entry = map.get(parentSpanId);
+  if (!entry) {
+    entry = {
+      checkpoints: new Map(),
+      listeners: new Set()
+    };
+    map.set(parentSpanId, entry);
+  }
+  return entry;
+}
+
+function performCleanup(kind: DisplayKind, parentSpanId: string, entry: SpanRegistry): void {
+  if (entry.checkpoints.size === 0 && entry.listeners.size === 0) {
+    registries[kind].delete(parentSpanId);
+  }
+}
+
+/**
+ * Register a checkpoint under (kind, parentSpanId). Returns an unregister fn.
+ */
+export function registerCheckpoint(
+  kind: DisplayKind,
+  parentSpanId: string,
+  checkpointId: string,
+  ready: boolean,
+): () => void {
+  const entry = getOrCreate(kind, parentSpanId);
+  entry.checkpoints.set(checkpointId, { ready });
+  notify(entry);
+
+  return () => {
+    const e = registries[kind].get(parentSpanId);
+    if (!e) {
+      return;
+    }
+    if (e.checkpoints.delete(checkpointId)) {
+      notify(e);
+    }
+    performCleanup(kind, parentSpanId, e);
+  };
+}
+
+/**
+ * Update an existing checkpoint's ready state.
+ */
+export function updateCheckpoint(
+  kind: DisplayKind,
+  parentSpanId: string,
+  checkpointId: string,
+  ready: boolean,
+): void {
+  const entry = registries[kind].get(parentSpanId);
+  const cp = entry?.checkpoints.get(checkpointId);
+  if (!entry || !cp || cp.ready === ready) {
+    return;
+  }
+  cp.ready = ready;
+  notify(entry);
+}
+
+/**
+ * True if at least one checkpoint is registered AND all checkpoints are ready.
+ */
+export function isAllReady(kind: DisplayKind, parentSpanId: string): boolean {
+  const entry = registries[kind].get(parentSpanId);
+  if (!entry || entry.checkpoints.size === 0) {
+    return false;
+  }
+  for (const cp of entry.checkpoints.values()) {
+    if (!cp.ready) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/**
+ * Returns true if there is at least one registered checkpoint on this span.
+ */
+export function hasAnyCheckpoints(kind: DisplayKind, parentSpanId: string): boolean {
+  const entry = registries[kind].get(parentSpanId);
+  return !!entry && entry.checkpoints.size > 0;
+}
+
+/**
+ * Subscribe to any checkpoint state change for a given span. The listener is
+ * called synchronously after each register/update/unregister event.
+ */
+export function subscribe(kind: DisplayKind, parentSpanId: string, listener: Listener): () => void {
+  const entry = getOrCreate(kind, parentSpanId);
+  entry.listeners.add(listener);
+  return () => {
+    const e = registries[kind].get(parentSpanId);
+    if (!e) {
+      return;
+    }
+    e.listeners.delete(listener);
+    performCleanup(kind, parentSpanId, e);
+  };
+}
+
+function notify(entry: SpanRegistry): void {
+  for (const listener of entry.listeners) {
+    listener();
+  }
+}
+
+/**
+ * Test-only. Clears all coordinator state.
+ */
+export function _resetTimeToDisplayCoordinator(): void {
+  registries.ttid.clear();
+  registries.ttfd.clear();
+}

packages/core/src/js/tracing/timetodisplay.tsx

@@ -13,12 +13,14 @@
   startInactiveSpan,
 } from '@sentry/core';
 import * as React from 'react';
-import { useState } from 'react';
+import { useEffect, useReducer, useRef, useState } from 'react';
 
 import type { NativeFramesResponse } from '../NativeRNSentry';
 
 import { NATIVE } from '../wrapper';
 import { SPAN_ORIGIN_AUTO_UI_TIME_TO_DISPLAY, SPAN_ORIGIN_MANUAL_UI_TIME_TO_DISPLAY } from './origin';
+import type { DisplayKind } from './timeToDisplayCoordinator';
+import { isAllReady, registerCheckpoint, subscribe, updateCheckpoint } from './timeToDisplayCoordinator';
 import { getRNSentryOnDrawReporter } from './timetodisplaynative';
 import { setSpanDurationAsMeasurement, setSpanDurationAsMeasurementOnSpan } from './utils';
 
@@ -59,15 +61,31 @@
 
 export type TimeToDisplayProps = {
   children?: React.ReactNode;
+  /**
+   * @deprecated Use `ready` instead. `record` and `ready` are equivalent;
+   * `record` will be removed in the next major version.
+   */
   record?: boolean;
+  /**
+   * Marks this checkpoint as ready. The display is recorded only when every
+   * `<TimeToFullDisplay>` / `<TimeToInitialDisplay>` mounted under the
+   * currently active span reports `ready === true`.
+   *
+   *   <TimeToFullDisplay ready={feedReady} />
+   *   <TimeToFullDisplay ready={sidebarReady} />
+   */
+  ready?: boolean;
 };
 
 /**
  * Component to measure time to initial display.
  *
- * The initial display is recorded when the component prop `record` is true.
+ * Single instance:
+ *   <TimeToInitialDisplay ready={isLoaded} />
  *
- * <TimeToInitialDisplay record />
+ * Multiple instances coordinating on one screen:
+ *   <TimeToInitialDisplay ready={headerLoaded} />
+ *   <TimeToInitialDisplay ready={contentLoaded} />
  */
 export function TimeToInitialDisplay(props: TimeToDisplayProps): React.ReactElement {
   const activeSpan = getActiveSpan();
@@ -76,8 +94,10 @@
   }
 
   const parentSpanId = activeSpan && spanToJSON(activeSpan).span_id;
+  const initialDisplay = useCoordinatedDisplay('ttid', parentSpanId, props);
+
   return (
-    <TimeToDisplay initialDisplay={props.record} parentSpanId={parentSpanId}>
+    <TimeToDisplay initialDisplay={initialDisplay} parentSpanId={parentSpanId}>
       {props.children}
     </TimeToDisplay>
   );
@@ -86,20 +106,93 @@
 /**
  * Component to measure time to full display.
  *
- * The initial display is recorded when the component prop `record` is true.
+ * Single instance:
+ *   <TimeToFullDisplay ready={isLoaded} />
  *
- * <TimeToInitialDisplay record />
+ * Multiple instances coordinating on one screen:
+ *   <TimeToFullDisplay ready={feedReady} />
+ *   <TimeToFullDisplay ready={sidebarReady} />
  */
 export function TimeToFullDisplay(props: TimeToDisplayProps): React.ReactElement {
   const activeSpan = getActiveSpan();
   const parentSpanId = activeSpan && spanToJSON(activeSpan).span_id;
+  const fullDisplay = useCoordinatedDisplay('ttfd', parentSpanId, props);
+
   return (
-    <TimeToDisplay fullDisplay={props.record} parentSpanId={parentSpanId}>
+    <TimeToDisplay fullDisplay={fullDisplay} parentSpanId={parentSpanId}>
       {props.children}
     </TimeToDisplay>
   );
 }
 
+/**
+ * Every `<TimeToInitialDisplay>` / `<TimeToFullDisplay>` instance registers as
+ * a checkpoint under the active span. The aggregate is ready if every
+ * checkpoint reports ready.
+ */
+/**
+ * Module-local counter used to mint stable, unique checkpoint ids per
+ * component instance without requiring React 18's `useId`.
+ */
+let nextCheckpointId = 0;
+
+function useCoordinatedDisplay(
+  kind: DisplayKind,
+  parentSpanId: string | undefined,
+  props: TimeToDisplayProps,
+): boolean {
+  // Stable per-instance id. `useRef` is available since React 16.8.
+  const checkpointIdRef = useRef<string | null>(null);
+  if (checkpointIdRef.current === null) {
+    checkpointIdRef.current = `cp-${nextCheckpointId++}`;
+  }
+  const checkpointId = checkpointIdRef.current;
+  const [, force] = useReducer((x: number) => x + 1, 0);
+
+  // `ready` takes precedence when both are provided.
+  const localReady = props.ready !== undefined ? !!props.ready : !!props.record;
+
+  if (__DEV__) {
+    if (props.ready !== undefined && props.record !== undefined) {
+      debug.warn('[TimeToDisplay] Both `ready` and `record` were provided — ignoring `record`.');
+    }
+    if (props.record !== undefined) {
+      debug.warn('[TimeToDisplay] The `record` prop is deprecated. Use `ready` instead.');
+    }
+  }
+
+  // Subscribe FIRST so this component receives its own registration notify
+  // (and any peer notifications) on mount.
+  useEffect(() => {
+    if (!parentSpanId) {
+      return undefined;
+    }
+    return subscribe(kind, parentSpanId, force);
+  }, [kind, parentSpanId]);
+
+  // Register on mount / when the active span changes; unregister on unmount.
+  useEffect(() => {
+    if (!parentSpanId) {
+      return undefined;
+    }
+    return registerCheckpoint(kind, parentSpanId, checkpointId, localReady);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [kind, parentSpanId, checkpointId]);
+
+  // Propagate ready transitions to the registry.
+  useEffect(() => {
+    if (!parentSpanId) {
+      return;
+    }
+    updateCheckpoint(kind, parentSpanId, checkpointId, localReady);
+  }, [kind, parentSpanId, checkpointId, localReady]);
+
+  if (!parentSpanId) {
+    return false;
+  }
+  return isAllReady(kind, parentSpanId);
+}
+
 function TimeToDisplay(props: {
   children?: React.ReactNode;
   initialDisplay?: boolean;