perf (fetch): use less promises for ReadableStream

[Uzlopak]

before the test used 19 promises. now it uses only 13.

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[KhafraDev]

Yes, undici might have less promises, but there's likely an equal number being created in node core. If we ignore node core, then what exactly are we testing?

[Uzlopak]

@KhafraDev
That is not true. The amount of promises stays the same in core. With node core before 57 promises are generated, after it generates 51.

Before:

{
  'new ReadableStream (node:internal/webstreams/readablestream:256:30)': 2,
  'setupReadableByteStreamController (node:internal/webstreams/readablestream:3290:5)': 2,
  'setupReadableByteStreamController (node:internal/webstreams/readablestream:3289:3)': 2,
  'Object.start (/home/aras/workspace/undici/lib/core/util.js:612:19)': 1,
  'createDeferredPromise (/home/aras/workspace/undici/lib/util/promise.js:18:19)': 1,
  'readableStreamReaderGenericInitialize (node:internal/webstreams/readablestream:2163:30)': 1,
  'readAllBytes (/home/aras/workspace/undici/lib/web/fetch/util.js:1026:29)': 1,
  'new DefaultReadRequest (node:internal/webstreams/readablestream:790:20)': 3,
  'readAllBytes (/home/aras/workspace/undici/lib/web/fetch/util.js:1032:51)': 3,
  'TestContext.<anonymous> (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:47:18)': 1,
  'node:internal/per_context/primordials:605:3': 1,
  'new SafePromise (node:internal/per_context/primordials:451:29)': 6,
  'node:internal/per_context/primordials:483:35': 2,
  'Test.run (node:internal/test_runner/test:1088:13)': 1,
  'Test.processPendingSubtests (node:internal/test_runner/test:763:18)': 1,
  'Promise.then (<anonymous>)': 4,
  'invokePromiseCallback (node:internal/webstreams/util:171:37)': 3,
  'pull (/home/aras/workspace/undici/lib/core/util.js:616:29)': 4,
  'pull (/home/aras/workspace/undici/lib/core/util.js:617:50)': 8,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:40:7)': 2,
  'readableByteStreamControllerCallPullIfNeeded (node:internal/webstreams/readablestream:3144:3)': 3,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:41:7)': 2,
  'pull (/home/aras/workspace/undici/lib/core/util.js:628:28)': 1,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:42:7)': 2
}

after:

{
  'new ReadableStream (node:internal/webstreams/readablestream:256:30)': 2,
  'setupReadableByteStreamController (node:internal/webstreams/readablestream:3290:5)': 2,
  'setupReadableByteStreamController (node:internal/webstreams/readablestream:3289:3)': 2,
  'createDeferredPromise (/home/aras/workspace/undici/lib/util/promise.js:18:19)': 1,
  'readableStreamReaderGenericInitialize (node:internal/webstreams/readablestream:2163:30)': 1,
  'readAllBytes (/home/aras/workspace/undici/lib/web/fetch/util.js:1026:29)': 1,
  'new DefaultReadRequest (node:internal/webstreams/readablestream:790:20)': 3,
  'readAllBytes (/home/aras/workspace/undici/lib/web/fetch/util.js:1032:51)': 3,
  'TestContext.<anonymous> (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:47:18)': 1,
  'node:internal/per_context/primordials:605:3': 1,
  'new SafePromise (node:internal/per_context/primordials:451:29)': 6,
  'node:internal/per_context/primordials:483:35': 2,
  'Test.run (node:internal/test_runner/test:1088:13)': 1,
  'Test.processPendingSubtests (node:internal/test_runner/test:763:18)': 1,
  'invokePromiseCallback (node:internal/webstreams/util:171:37)': 3,
  'Object.pull (/home/aras/workspace/undici/lib/core/util.js:616:25)': 4,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:40:7)': 2,
  'Object.pull (/home/aras/workspace/undici/lib/core/util.js:616:32)': 4,
  'readableByteStreamControllerCallPullIfNeeded (node:internal/webstreams/readablestream:3144:3)': 3,
  'Promise.then (<anonymous>)': 4,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:41:7)': 2,
  '[Symbol.asyncIterator] (/home/aras/workspace/undici/test/fetch/readable-stream-from.js:42:7)': 2
}

[mcollina]

lgtm - removing as many as possible would speed us up a tiny bit. Note that this code is functionally equivalent, so there is no downside here.

[KhafraDev]

That is not true. The amount of promises stays the same in core. With node core before 57 promises are generated, after it generates 51.

What isn't true? The whole point is that if we are counting the number of promises in webstreams, we should include the ones from node core. After I made that comment I had to dig into the streams spec to find how the value was getting wrapped in a promise (in a sane world I would have expected startAlgorithm instanceof Promise ? startAlgorithm : Promise.resolve(startAlgorithm))

[Uzlopak]

@KhafraDev

I cant write a test for created Promises in node core. I tried that but it is not working, because the created Promises are different on versions of nodejs. I could write tests based on the nodejs version, if this solves the blocking.