feat: run background revalidation at end of response

packages/next/package.json

@@ -273,6 +273,7 @@
     "node-html-parser": "5.3.3",
     "ora": "4.0.4",
     "os-browserify": "0.3.0",
+    "p-lazy": "3.1.0",
     "p-limit": "3.1.0",
     "p-queue": "6.6.2",
     "path-browserify": "1.0.1",

packages/next/src/compiled/p-lazy/LICENSE

@@ -0,0 +1,9 @@
+MIT License
+
+Copyright (c) Sindre Sorhus <sindresorhus@gmail.com> (sindresorhus.com)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

packages/next/src/compiled/p-lazy/package.json

@@ -0,0 +1 @@
+{"name":"p-lazy","main":"index.js","author":{"name":"Sindre Sorhus","email":"sindresorhus@gmail.com","url":"sindresorhus.com"},"license":"MIT"}

packages/next/src/lib/scheduler.ts

@@ -1,3 +1,5 @@
+import PLazy from 'next/dist/compiled/p-lazy'
+
 export type ScheduledFn<T = void> = () => T | PromiseLike<T>
 export type SchedulerFn<T = void> = (cb: ScheduledFn<T>) => void
 
@@ -58,3 +60,14 @@ export function waitAtLeastOneReactRenderTask(): Promise<void> {
     return new Promise((r) => setImmediate(r))
   }
 }
+
+/**
+ * This will create a promise that will not have it's executor run until the
+ * promise is awaited.
+ *
+ * @param fn the function to execute
+ * @returns a promise that will resolve with the return value of the function
+ */
+export const scheduleLazily = async <T>(fn: () => Promise<T>) => {
+  return new PLazy<T>((resolve) => fn().then(resolve))
+}

packages/next/src/server/after/after-context.ts

@@ -26,8 +26,7 @@ export class AfterContext {
     this.waitUntil = waitUntil
     this.onClose = onClose
 
-    this.callbackQueue = new PromiseQueue()
-    this.callbackQueue.pause()
+    this.callbackQueue = new PromiseQueue({ autoStart: false })
   }
 
   public run<T>(requestStore: RequestStore, callback: () => T): T {
@@ -105,8 +104,7 @@ export class AfterContext {
       wrapRequestStoreForAfterCallbacks(requestStore)
 
     return requestAsyncStorage.run(readonlyRequestStore, () => {
-      this.callbackQueue.start()
-      return this.callbackQueue.onIdle()
+      return this.callbackQueue.start().onIdle()
     })
   }
 }

packages/next/src/server/after/noop-wait-until.ts

@@ -0,0 +1,5 @@
+export function noopWaitUntil(promise: Promise<any>) {
+  promise.catch((err: unknown) => {
+    console.error(err)
+  })
+}

packages/next/src/server/base-server.ts

@@ -168,7 +168,8 @@ import { RouteKind } from './route-kind'
 import type { RouteModule } from './route-modules/route-module'
 import { FallbackMode, parseFallbackField } from '../lib/fallback'
 import { toResponseCacheEntry } from './response-cache/utils'
-import { scheduleOnNextTick } from '../lib/scheduler'
+import { scheduleLazily } from '../lib/scheduler'
+import { noopWaitUntil } from './after/noop-wait-until'
 
 export type FindComponentsResult = {
   components: LoadComponentsReturnType
@@ -1739,7 +1740,7 @@ export default abstract class Server<
 
     if (process.env.__NEXT_TEST_MODE) {
       // we're in a test, use a no-op.
-      return Server.noopWaitUntil
+      return noopWaitUntil
     }
 
     if (this.minimalMode || process.env.NEXT_RUNTIME === 'edge') {
@@ -1751,13 +1752,7 @@ export default abstract class Server<
     }
 
     // we're in `next start` or `next dev`. noop is fine for both.
-    return Server.noopWaitUntil
-  }
-
-  private static noopWaitUntil(promise: Promise<any>) {
-    promise.catch((err: unknown) => {
-      console.error(err)
-    })
+    return noopWaitUntil
   }
 
   private async renderImpl(
@@ -2984,39 +2979,47 @@ export default abstract class Server<
     }
 
     // If we're not in minimal mode and the cache entry that was returned was a
-    // app page fallback, then we need to kick off the dynamic shell generation.
+    // app page fallback, then we need to kick off the route shell generation.
     if (
       ssgCacheKey &&
       !this.minimalMode &&
       isRoutePPREnabled &&
       this.nextConfig.experimental.pprFallbacks &&
       cacheEntry.value?.kind === CachedRouteKind.APP_PAGE &&
       cacheEntry.isFallback &&
-      !isOnDemandRevalidate
+      !isOnDemandRevalidate &&
+      process.env.NEXT_RUNTIME !== 'edge'
     ) {
-      scheduleOnNextTick(async () => {
-        try {
-          await this.responseCache.get(
-            ssgCacheKey,
-            () =>
-              doRender({
-                // We're an on-demand request, so we don't need to pass in the
-                // fallbackRouteParams.
-                fallbackRouteParams: null,
-                postponed: undefined,
-              }),
-            {
-              routeKind: RouteKind.APP_PAGE,
-              incrementalCache,
-              isOnDemandRevalidate: true,
-              isPrefetch: false,
-              isRoutePPREnabled: true,
-            }
-          )
-        } catch (err) {
-          console.error('Error occurred while rendering dynamic shell', err)
-        }
-      })
+      // Wait until the response is completed sending before we start the
+      // background revalidation. Attaching this to the `waitUntil` queue on the
+      // render result will not hold the request open until the revalidation is
+      // completed but instead will just delay the time it starts the
+      // revalidation.
+      cacheEntry.value.html.waitUntil(
+        scheduleLazily(() => {
+          this.responseCache
+            .get(
+              ssgCacheKey,
+              () =>
+                doRender({
+                  // We're an on-demand request, so we don't need to pass in the
+                  // fallbackRouteParams.
+                  fallbackRouteParams: null,
+                  postponed: undefined,
+                }),
+              {
+                routeKind: RouteKind.APP_PAGE,
+                incrementalCache,
+                isOnDemandRevalidate: true,
+                isPrefetch: false,
+                isRoutePPREnabled: true,
+              }
+            )
+            .catch((err) => {
+              console.error('Error occurred while rendering route shell', err)
+            })
+        })
+      )
     }
 
     const didPostpone =

packages/next/src/server/render-result.ts

@@ -2,6 +2,7 @@ import type { OutgoingHttpHeaders, ServerResponse } from 'http'
 import type { Revalidate } from './lib/revalidate'
 import type { FetchMetrics } from './base-http'
 
+import PQueue from 'next/dist/compiled/p-queue'
 import {
   chainStreams,
   streamFromBuffer,
@@ -10,6 +11,7 @@ import {
   streamToString,
 } from './stream-utils/node-web-streams-helper'
 import { isAbortError, pipeToNodeResponse } from './pipe-readable'
+import { scheduleLazily } from '../lib/scheduler'
 
 type ContentTypeOption = string | undefined
 
@@ -96,7 +98,7 @@ export default class RenderResult<
     return new RenderResult<StaticRenderResultMetadata>(value, { metadata: {} })
   }
 
-  private readonly waitUntil?: Promise<unknown>
+  private readonly waitUntilQueue: PQueue = new PQueue({ autoStart: false })
 
   constructor(
     response: RenderResultResponse,
@@ -105,7 +107,14 @@ export default class RenderResult<
     this.response = response
     this.contentType = contentType
     this.metadata = metadata
-    this.waitUntil = waitUntil
+
+    if (waitUntil) {
+      this.waitUntilQueue.add(() => waitUntil)
+    }
+  }
+
+  public waitUntil(promise: Promise<unknown>) {
+    this.waitUntilQueue.add(() => promise)
   }
 
   public assignMetadata(metadata: Metadata) {
@@ -250,7 +259,9 @@ export default class RenderResult<
 
       // If there is a waitUntil promise, wait for it to resolve before
       // closing the writable stream.
-      if (this.waitUntil) await this.waitUntil
+      if (this.waitUntilQueue.size > 0) {
+        await this.waitUntilQueue.start().onIdle()
+      }
 
       // Close the writable stream.
       await writable.close()
@@ -279,6 +290,18 @@ export default class RenderResult<
    * @param res
    */
   public async pipeToNodeResponse(res: ServerResponse) {
-    await pipeToNodeResponse(this.readable, res, this.waitUntil)
+    await pipeToNodeResponse(
+      this.readable,
+      res,
+      // Create a promise that will only run this callback when it's awaited. It
+      // will start the queue and wait until all the tasks are done.
+      scheduleLazily(() => {
+        if (this.waitUntilQueue.size === 0) {
+          return Promise.resolve()
+        }
+
+        return this.waitUntilQueue.start().onIdle()
+      })
+    )
   }
 }

packages/next/taskfile.js

@@ -664,6 +664,14 @@ export async function ncc_p_queue(task, opts) {
     .ncc({ packageName: 'p-queue', externals })
     .target('src/compiled/p-queue')
 }
+// eslint-disable-next-line camelcase
+externals['p-lazy'] = 'next/dist/compiled/p-lazy'
+export async function ncc_p_lazy(task, opts) {
+  await task
+    .source(relative(__dirname, require.resolve('p-lazy')))
+    .ncc({ packageName: 'p-lazy', externals })
+    .target('src/compiled/p-lazy')
+}
 
 // eslint-disable-next-line camelcase
 externals['raw-body'] = 'next/dist/compiled/raw-body'
@@ -2280,6 +2288,7 @@ export async function ncc(task, opts) {
         'ncc_napirs_triples',
         'ncc_p_limit',
         'ncc_p_queue',
+        'ncc_p_lazy',
         'ncc_raw_body',
         'ncc_image_size',
         'ncc_hapi_accept',

packages/next/types/$$compiled.internal.d.ts

@@ -86,6 +86,11 @@ declare module 'next/dist/compiled/p-queue' {
   export = m
 }
 
+declare module 'next/dist/compiled/p-lazy' {
+  import m from 'p-lazy'
+  export = m
+}
+
 declare module 'next/dist/compiled/raw-body' {
   import m from 'raw-body'
   export = m