[Flight] Optimize Retention of Weak Promises Abit #33736
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eps1lon
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Jul 9, 2025
sebmarkbage
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Jul 9, 2025
Follow up to #33736. If we need to save on CPU/memory pressure, we can instead just pray and hope that a Promise doesn't get garbage collected before we need to read it. This can cause fragile access to the Promise value in devtools especially if it's a slow and pressured render. Basically, you'd have to hope that GC doesn't run after the inner await finishes its microtask callback and before the resolution of the component being rendered is invoked.
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When running the following test isolated, and not as part of the full test suite, the owner stacks for async I/O errors were missing the top-most stack frame that's pointing at the `fetch` call. ``` pnpm test-dev test/e2e/app-dir/dynamic-io-errors/dynamic-io-errors.test.ts -t "should show a collapsed redbox with two errors" ``` The same could be reproduced with `pnpm next dev test/e2e/app-dir/dynamic-io-errors/fixtures/default` at http://localhost:3000/dynamic-root, unless http://localhost:3000/static was visited first. The likely reason for that is that React's async I/O tracking was recently optimized for performance reasons in facebook/react#33736 and facebook/react#33737. We can help React a bit with the tracking by explicitly awaiting our `makeHangingPromise` calls. With this fix, the case from above reliably works in isolation.
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When running the following test isolated, and not as part of the full test suite, the owner stacks for async I/O errors were missing the top-most stack frame that's pointing at the `fetch` call. ``` pnpm test-dev test/e2e/app-dir/dynamic-io-errors/dynamic-io-errors.test.ts -t "should show a collapsed redbox with two errors" ``` The same could be reproduced with `pnpm next dev test/e2e/app-dir/dynamic-io-errors/fixtures/default` at http://localhost:3000/dynamic-root, unless http://localhost:3000/static was visited first. The likely reason for that is that React's async I/O tracking was recently optimized for performance reasons in facebook/react#33736 and facebook/react#33737. We can help React a bit with the tracking by explicitly awaiting our `makeHangingPromise` calls. With this fix, the case from above reliably works in isolation.
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Jul 14, 2025
When running the following test isolated, and not as part of the full test suite, the owner stacks for async I/O errors were missing the top-most stack frame that's pointing at the `fetch` call. ``` pnpm test-dev test/e2e/app-dir/dynamic-io-errors/dynamic-io-errors.test.ts -t "should show a collapsed redbox with two errors" ``` The same could be reproduced with `pnpm next dev test/e2e/app-dir/dynamic-io-errors/fixtures/default` at http://localhost:3000/dynamic-root, unless http://localhost:3000/static was visited first. The likely reason for that is that React's async I/O tracking was recently optimized for performance reasons in facebook/react#33736 and facebook/react#33737. We can help React a bit with the tracking by explicitly awaiting our `makeHangingPromise` calls. With this fix, the case from above reliably works in isolation.
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Jul 15, 2025
When running the following test isolated, and not as part of the full test suite, the owner stacks for async I/O errors were missing the top-most stack frame that's pointing at the `fetch` call. ``` pnpm test-dev test/e2e/app-dir/dynamic-io-errors/dynamic-io-errors.test.ts -t "should show a collapsed redbox with two errors" ``` The same could be reproduced with `pnpm next dev test/e2e/app-dir/dynamic-io-errors/fixtures/default` at http://localhost:3000/dynamic-root, unless http://localhost:3000/static was visited first. The likely reason for that is that React's async I/O tracking was recently optimized for performance reasons in facebook/react#33736 and facebook/react#33737. We can help React a bit with the tracking by explicitly awaiting our `makeHangingPromise` calls. With this fix, the case from above reliably works in isolation.
unstubbable
added a commit
to vercel/next.js
that referenced
this pull request
Jul 15, 2025
When running the following test isolated, and not as part of the full test suite, the owner stacks for async I/O errors were missing the top-most stack frame that's pointing at the `fetch` call. ``` pnpm test-dev test/e2e/app-dir/dynamic-io-errors/dynamic-io-errors.test.ts -t "should show a collapsed redbox with two errors" ``` The same could be reproduced with `pnpm next dev test/e2e/app-dir/dynamic-io-errors/fixtures/default` at http://localhost:3000/dynamic-root, unless http://localhost:3000/static was visited first. The likely reason for that is that React's async I/O tracking was recently optimized for performance reasons in facebook/react#33736 and facebook/react#33737. We can help React a bit with the tracking by explicitly awaiting our `makeHangingPromise` calls. With this fix, the case from above reliably works in isolation.
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We don't really need to retain a reference to whatever Promise another Promise was created in. Only awaits need to retain both their trigger and their previous context.