mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
b8e678b765
events.once(process.stdout, name) with a name typed "drain" returned the pending promise without evaluating the name, so a call or comma expression producing "drain" never ran. A name that is not a string literal now runs before the promise is created. A write completion callback that returns a value (`() => count++`, a stored function typed `(): number`) reported SC2020. The stream ignores the return value, so such a callback is adapted to return nothing, as before the error-argument form was added. The stream-shims npm case compiles and matches Node now that write callbacks take the error argument, so its SC2020 expectation is removed.
57 lines
1.9 KiB
TypeScript
57 lines
1.9 KiB
TypeScript
// process.stdout/stderr backpressure probes under the synchronous stream
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// model: every write reaches the descriptor before write() returns, so
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// nothing is ever queued. writableLength is 0, writableNeedDrain is false,
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// write() returns true, and 'drain' (emitted only after a write returned
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// false) never fires: drain listeners register and stay silent, and a
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// promise of the next drain never settles without holding the process.
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import { once } from "node:events";
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console.log("hwm", process.stdout.writableHighWaterMark, process.stderr.writableHighWaterMark);
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console.log("needDrain", process.stdout.writableNeedDrain, process.stderr.writableNeedDrain);
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console.log("length", process.stdout.writableLength, process.stderr.writableLength);
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let drained = 0;
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const onDrain = (): void => {
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drained++;
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};
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process.stdout.on("drain", onDrain);
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process.stdout.once("drain", () => {
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drained++;
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});
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process.stderr.addListener("drain", onDrain);
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process.stdout.off("drain", onDrain);
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process.stderr.removeListener("drain", onDrain);
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const ok = process.stdout.write("chunk\n");
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console.log("write returned", ok);
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// The flush idiom: wait for drain only when bytes are queued or the
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// write asked for it.
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async function flush(): Promise<void> {
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if (process.stdout.writableLength > 0) {
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await new Promise<void>((resolve) => process.stdout.once("drain", resolve));
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}
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if (!process.stdout.write("again\n")) await once(process.stdout, "drain");
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console.log("flushed");
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}
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void flush();
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// A drain that cannot come: the promise stays pending, and the process
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// exits once the loop is empty.
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void (async () => {
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await once(process.stderr, "drain");
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console.log("never");
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})();
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// A name expression typed "drain" still runs.
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let picks = 0;
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const drainName = (): "drain" => {
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picks++;
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return "drain";
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};
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void once(process.stdout, drainName());
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void once(process.stderr, (picks++, "drain"));
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console.log("picks", picks);
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setTimeout(() => console.log("drained", drained), 5);
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