[pull] main from facebook:main #355
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500 tests failed from not using async act. Will fix the tests and then re-land this.
…35003) IO tasks can execute more than once. E.g. a connection may fire each time a new message or chunk comes in or a setInterval every time it executes. We used to treat these all as one I/O node and just updated the end time as we go. Most of the time this was fine because typically you would have a Promise instance whose end time is really the one that gets used as the I/O anyway. However, in a pattern like this it could be problematic: ```js setTimeout(() => { function App() { return Promise.resolve(123); } renderToReadableStream(<App />); }); ``` Because the I/O's end time is before the render started so it should be excluded from being considered I/O as part of the render. It happened outside of render. But because the `Promise.resolve()` is inside render its end time is after the render start so the promise is considered part of the render. This is usually not a problem because the end time of the I/O is still before the start of the render so even though the Promise is valid it has no I/O source so it's properly excluded. However, if the I/O's end time updates before we observe this then the I/O can be considered part of the render. E.g. if this was a setInterval it would be clearly wrong. But it turns out that even setTimeout can sometimes execute more than once in the async_hooks because each run of "process.nextTick" and microtasks respectively are ran in their own before/after. When a micro task executes after this main body it'll update the end time which can then turn the whole I/O as being inside the render. To solve this properly I create a new I/O node each time before() is invoked so that each one gets to observe a different end time. This has a potential CPU and memory allocation cost when there's a lot of them like in a quick stream.
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