Repository: facebook/react
Pull request: [DevTools] Track Tree Base Duration of Virtual Instances

These don't have their own time since they don't take up any time to render but they show up in the tree for context. However they never render themselves. Their base tree time is the base time of their children. This way they take up the same space as their combined children in the Profiler tree. (Instead of leaving a blank line which they did before this PR.)

The frontend doesn't track the difference between a virtual instance and a Fiber that didn't render this update. This might be a bit confusing as to why it didn't render. I add the word "client" to make it a bit clearer and works for both. We should probably have different verbiage here based on it is a Server Component or something else.

<img width="1103" alt="Screenshot 2024-08-26 at 5 00 47 PM" src="https://github.com/user-attachments/assets/87b811d4-7024-466a-845d-542493ed3ca2">

I also took the opportunity to remove idToTreeBaseDurationMap and idToRootMap maps. Cloning the Map isn't really all that super fast anyway and it means we have to maintain the map continuously as we render. Instead, we can track it on the instances and then walk the instances to create a snapshot when starting to profile. This isn't as fast but really fast too and requires less bookkeeping while rendering instead which is more sensitive than that one snapshot in the beginning.

Changed files:
filename: packages/react-devtools-shared/src/backend/fiber/renderer.js
patch: @@ -164,6 +164,7 @@ type FiberInstance = {
   source: null | string | Error | Source, // source location of this component function, or owned child stack
   errors: null | Map<string, number>, // error messages and count
   warnings: null | Map<string, number>, // warning messages and count
+  treeBaseDuration: number, // the profiled time of the last render of this subtree
   data: Fiber, // one of a Fiber pair
 };
 
@@ -179,6 +180,7 @@ function createFiberInstance(fiber: Fiber): FiberInstance {
     source: null,
     errors: null,
     warnings: null,
+    treeBaseDuration: 0,
     data: fiber,
   };
 }
@@ -202,6 +204,7 @@ type VirtualInstance = {
   // that old errors/warnings don't disappear when the instance is refreshed.
   errors: null | Map<string, number>, // error messages and count
   warnings: null | Map<string, number>, // warning messages and count
+  treeBaseDuration: number, // the profiled time of the last render of this subtree
   // The latest info for this instance. This can be updated over time and the
   // same info can appear in more than once ServerComponentInstance.
   data: ReactComponentInfo,
@@ -221,6 +224,7 @@ function createVirtualInstance(
     source: null,
     errors: null,
     warnings: null,
+    treeBaseDuration: 0,
     data: debugEntry,
   };
 }
@@ -1355,16 +1359,6 @@ export function attach(
     }
   }
 
-  // When profiling is supported, we store the latest tree base durations for each Fiber.
-  // This is so that we can quickly capture a snapshot of those values if profiling starts.
-  // If we didn't store these values, we'd have to crawl the tree when profiling started,
-  // and use a slow path to find each of the current Fibers.
-  const idToTreeBaseDurationMap: Map<number, number> = new Map();
-
-  // When profiling is supported, we store the latest tree base durations for each Fiber.
-  // This map enables us to filter these times by root when sending them to the frontend.
-  const idToRootMap: Map<number, number> = new Map();
-
   // When a mount or update is in progress, this value tracks the root that is being operated on.
   let currentRootID: number = -1;
 
@@ -2211,9 +2205,7 @@ export function attach(
     }
 
     if (isProfilingSupported) {
-      idToRootMap.set(id, currentRootID);
-
-      recordProfilingDurations(fiber);
+      recordProfilingDurations(fiberInstance);
     }
     return fiberInstance;
   }
@@ -2226,8 +2218,6 @@ export function attach(
 
     idToDevToolsInstanceMap.set(id, instance);
 
-    const isProfilingSupported = false; // TODO: Support Tree Base Duration Based on Children.
-
     const componentInfo = instance.data;
 
     const key =
@@ -2274,12 +2264,6 @@ export function attach(
     pushOperation(ownerID);
     pushOperation(displayNameStringID);
     pushOperation(keyStringID);
-
-    if (isProfilingSupported) {
-      idToRootMap.set(id, currentRootID);
-      // TODO: Include tree base duration of children somehow.
-      // recordProfilingDurations(...);
-    }
   }
 
   function recordUnmount(fiberInstance: FiberInstance): void {
@@ -2314,12 +2298,6 @@ export function attach(
     }
 
     untrackFiber(fiberInstance);
-
-    const isProfilingSupported = fiber.hasOwnProperty('treeBaseDuration');
-    if (isProfilingSupported) {
-      idToRootMap.delete(id);
-      idToTreeBaseDurationMap.delete(id);
-    }
   }
 
   // Running state of the remaining children from the previous version of this parent that
@@ -2430,6 +2408,8 @@ export function attach(
         traceNearestHostComponentUpdate,
         virtualLevel + 1,
       );
+      // Must be called after all children have been appended.
+      recordVirtualProfilingDurations(virtualInstance);
     } finally {
       reconcilingParent = stashedParent;
       previouslyReconciledSibling = stashedPrevious;
@@ -2445,12 +2425,6 @@ export function attach(
 
     const id = instance.id;
     pendingRealUnmountedIDs.push(id);
-
-    const isProfilingSupported = false; // TODO: Profiling support.
-    if (isProfilingSupported) {
-      idToRootMap.delete(id);
-      idToTreeBaseDurationMap.delete(id);
-    }
   }
 
   function mountVirtualChildrenRecursively(
@@ -2684,11 +2658,12 @@ export function attach(
     removeChild(instance);
   }
 
-  function recordProfilingDurations(fiber: Fiber) {
-    const id = getFiberIDThrows(fiber);
+  function recordProfilingDurations(fiberInstance: FiberInstance) {
+    const id = fiberInstance.id;
+    const fiber = fiberInstance.data;
     const {actualDuration, treeBaseDuration} = fiber;
 
-    idToTreeBaseDurationMap.set(id, treeBaseDuration || 0);
+    fiberInstance.treeBaseDuration = treeBaseDuration || 0;
 
     if (isProfiling) {
       const {alternate} = fiber;
@@ -2751,6 +2726,38 @@ export function attach(
     }
   }
 
+  function recordVirtualProfilingDurations(virtualInstance: VirtualInstance) {
+    const id = virtualInstance.id;
+
+    let treeBaseDuration = 0;
+    // Add up the base duration of the child instances. The virtual base duration
+    // will be the same as children's duration since we don't take up any render
+    // time in the virtual instance.
+    for (
+      let child = virtualInstance.firstChild;
+      child !== null;
+      child = child.nextSibling
+    ) {
+      treeBaseDuration += child.treeBaseDuration;
+    }
+
+    if (isProfiling) {
+      const previousTreeBaseDuration = virtualInstance.treeBaseDuration;
+      if (treeBaseDuration !== previousTreeBaseDuration) {
+        // Tree base duration updates are included in the operations typed array.
+        // So we have to convert them from milliseconds to microseconds so we can send them as ints.
+        const convertedTreeBaseDuration = Math.floor(
+          (treeBaseDuration || 0) * 1000,
+        );
+        pushOperation(TREE_OPERATION_UPDATE_TREE_BASE_DURATION);
+        pushOperation(id);
+        pushOperation(convertedTreeBaseDuration);
+      }
+    }
+
+    virtualInstance.treeBaseDuration = treeBaseDuration;
+  }
+
   function recordResetChildren(parentInstance: DevToolsInstance) {
     if (__DEBUG__) {
       if (
@@ -2818,6 +2825,8 @@ export function attach(
       ) {
         recordResetChildren(virtualInstance);
       }
+      // Must be called after all children have been appended.
+      recordVirtualProfilingDurations(virtualInstance);
     } finally {
       unmountRemainingChildren();
       reconcilingParent = stashedParent;
@@ -3265,11 +3274,11 @@ export function attach(
         }
       }
 
-      if (shouldIncludeInTree) {
+      if (fiberInstance !== null) {
         const isProfilingSupported =
           nextFiber.hasOwnProperty('treeBaseDuration');
         if (isProfilingSupported) {
-          recordProfilingDurations(nextFiber);
+          recordProfilingDurations(fiberInstance);
         }
       }
       if (shouldResetChildren) {
@@ -5121,8 +5130,8 @@ export function attach(
   let currentCommitProfilingMetadata: CommitProfilingData | null = null;
   let displayNamesByRootID: DisplayNamesByRootID | null = null;
   let idToContextsMap: Map<number, any> | null = null;
-  let initialTreeBaseDurationsMap: Map<number, number> | null = null;
-  let initialIDToRootMap: Map<number, number> | null = null;
+  let initialTreeBaseDurationsMap: Map<number, Array<[number, number]>> | null =
+    null;
   let isProfiling: boolean = false;
   let profilingStartTime: number = 0;
   let recordChangeDescriptions: boolean = false;
@@ -5141,24 +5150,15 @@ export function attach(
     rootToCommitProfilingMetadataMap.forEach(
       (commitProfilingMetadata, rootID) => {
         const commitData: Array<CommitDataBackend> = [];
-        const initialTreeBaseDurations: Array<[number, number]> = [];
 
         const displayName =
           (displayNamesByRootID !== null && displayNamesByRootID.get(rootID)) ||
           'Unknown';
 
-        if (initialTreeBaseDurationsMap != null) {
-          initialTreeBaseDurationsMap.forEach((treeBaseDuration, id) => {
-            if (
-              initialIDToRootMap != null &&
-              initialIDToRootMap.get(id) === rootID
-            ) {
-              // We don't need to convert milliseconds to microseconds in this case,
-              // because the profiling summary is JSON serialized.
-              initialTreeBaseDurations.push([id, treeBaseDuration]);
-            }
-          });
-        }
+        const initialTreeBaseDurations: Array<[number, number]> =
+          (initialTreeBaseDurationsMap !== null &&
+            initialTreeBaseDurationsMap.get(rootID)) ||
+          [];
 
         commitProfilingMetadata.forEach((commitProfilingData, commitIndex) => {
           const {
@@ -5245,6 +5245,22 @@ export function attach(
     };
   }
 
+  function snapshotTreeBaseDurations(
+    instance: DevToolsInstance,
+    target: Array<[number, number]>,
+  ) {
+    // We don't need to convert milliseconds to microseconds in this case,
+    // because the profiling summary is JSON serialized.
+    target.push([instance.id, instance.treeBaseDuration]);
+    for (
+      let child = instance.firstChild;
+      child !== null;
+      child = child.nextSibling
+    ) {
+      snapshotTreeBaseDurations(child, target);
+    }
+  }
+
   function startProfiling(shouldRecordChangeDescriptions: boolean) {
     if (isProfiling) {
       return;
@@ -5257,16 +5273,19 @@ export function attach(
     // since either of these may change during the profiling session
     // (e.g. when a fiber is re-rendered or when a fiber gets removed).
     displayNamesByRootID = new Map();
-    initialTreeBaseDurationsMap = new Map(idToTreeBaseDurationMap);
-    initialIDToRootMap = new Map(idToRootMap);
+    initialTreeBaseDurationsMap = new Map();
     idToContextsMap = new Map();
 
     hook.getFiberRoots(rendererID).forEach(root => {
-      const rootID = getFiberIDThrows(root.current);
+      const rootInstance = getFiberInstanceThrows(root.current);
+      const rootID = rootInstance.id;
       ((displayNamesByRootID: any): DisplayNamesByRootID).set(
         rootID,
         getDisplayNameForRoot(root.current),
       );
+      const initialTreeBaseDurations: Array<[number, number]> = [];
+      snapshotTreeBaseDurations(rootInstance, initialTreeBaseDurations);
+      (initialTreeBaseDurationsMap: any).set(rootID, initialTreeBaseDurations);
 
       if (shouldRecordChangeDescriptions) {
         // Record all contexts at the time profiling is started.

filename: packages/react-devtools-shared/src/devtools/views/Profiler/HoveredFiberInfo.js
patch: @@ -93,7 +93,7 @@ export default function HoveredFiberInfo({fiberData}: Props): React.Node {
         )}
 
         <div className={styles.Content}>
-          {renderDurationInfo || <div>Did not render.</div>}
+          {renderDurationInfo || <div>Did not client render.</div>}
 
           <WhatChanged fiberID={id} />
         </div>

filename: packages/react-devtools-shared/src/devtools/views/Profiler/SidebarSelectedFiberInfo.js
patch: @@ -142,7 +142,7 @@ export default function SidebarSelectedFiberInfo(): React.Node {
           </div>
         )}
         {listItems.length === 0 && (
-          <div>Did not render during this profiling session.</div>
+          <div>Did not render on the client during this profiling session.</div>
         )}
       </div>
     </Fragment>