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stream: speed up WHATWG web streams#65273
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -111,6 +111,7 @@ const { | ||
| extractSizeAlgorithm, | ||
| getNonWritablePropertyDescriptor, | ||
| isBrandCheck, | ||
| isNonThenable, | ||
| kEmptyQueue, | ||
| kResolvedPromise, | ||
| kState, | ||
| @@ -252,6 +253,16 @@ class ReadableStream { | ||
| */ | ||
| constructor(source = kEmptyObject, strategy = kEmptyObject) { | ||
| markTransferMode(this, false, true); | ||
| // Empty-argument `new ReadableStream()`: no source, no strategy, and | ||
| // no controller. Reads never deliver data, so skip those allocations | ||
| // until getReader/cancel/error first need a default controller. | ||
| // Subclasses that call those methods after super() materialize the | ||
| // controller in the subclass constructor; see | ||
| // ensureEmptyDefaultController. | ||
| if (source === kEmptyObject && strategy === kEmptyObject) { | ||
| this[kState] = createReadableStreamState(); | ||
| return; | ||
| } | ||
| validateObject(source, 'source', kValidateObjectAllowObjects); | ||
| validateObject(strategy, 'strategy', kValidateObjectAllowObjectsAndNull); | ||
| this[kState] = createReadableStreamState(); | ||
| @@ -301,8 +312,14 @@ class ReadableStream { | ||
| // only default controllers were wired here; byte stream controllers | ||
| // keep the previous no-op behavior. | ||
| const controller = this[kState].controller; | ||
| if (controller === undefined) { | ||
| if (this[kState].state === 'readable') { | ||
| readableStreamError(this, error); | ||
| } | ||
| return; | ||
| } | ||
| if (isReadableStreamDefaultController(controller)) | ||
| readableStreamDefaultControllerError(controller, error); | ||
| } | ||
| // Used by the internal stream interop (end-of-stream). Materialized | ||
| @@ -351,6 +368,10 @@ class ReadableStream { | ||
| return PromiseReject( | ||
| new ERR_INVALID_STATE.TypeError('ReadableStream is locked')); | ||
| } | ||
| // Only materialize the deferred empty controller when cancel will | ||
| // actually run cancel steps. closed/errored streams return immediately. | ||
| if (this[kState].state === 'readable') | ||
| ensureEmptyDefaultController(this); | ||
| return readableStreamCancel(this, reason); | ||
| } | ||
| @@ -1422,6 +1443,7 @@ function createReadableStreamState() { | ||
| return { | ||
| __proto__: null, | ||
| closedPromise: undefined, | ||
| controller: undefined, | ||
| disturbed: false, | ||
| reader: undefined, | ||
| state: 'readable', | ||
| @@ -2580,6 +2602,7 @@ function setupReadableStreamBYOBReader(reader, stream) { | ||
| function setupReadableStreamDefaultReader(reader, stream) { | ||
| if (isReadableStreamLocked(stream)) | ||
| throw new ERR_INVALID_STATE.TypeError('ReadableStream is locked'); | ||
| ensureEmptyDefaultController(stream); | ||
| readableStreamReaderGenericInitialize(reader, stream); | ||
| reader[kState].readRequests = kEmptyQueue; | ||
| } | ||
| @@ -2729,7 +2752,8 @@ function readableStreamDefaultControllerPull(controller) { | ||
| // The pull algorithm may be a raw callback (a wrapped user source.pull | ||
| // returns its result uncoerced; a synchronous throw surfaces here) or an | ||
| // internal algorithm that always returns a promise; thenAlgorithmResult | ||
| // handles both. Non-thenable results react on kResolvedPromise so each | ||
| // pull is still separated by a microtask, matching the spec. | ||
| let result; | ||
| try { | ||
| result = controller[kState].pullAlgorithm(controller); | ||
| @@ -2796,6 +2820,43 @@ function readableStreamDefaultControllerPullSteps(controller, readRequest) { | ||
| readableStreamDefaultControllerPull(controller); | ||
| } | ||
| // Materialize the deferred default controller for `new ReadableStream()`. | ||
| // | ||
| // started is true immediately: the empty-argument start algorithm is a | ||
| // no-op, so there is no initial pull and nothing can observe an unstarted | ||
| // controller without first calling getReader/cancel/pipeTo/tee/values, | ||
| // all of which come through here. That is also why this still matches | ||
| // WPT: those tests either pass a source (leaving this path) or wait for | ||
| // start, which is already complete for a no-op start. | ||
| // | ||
| // Subclasses that call cancel(), getReader(), pipeTo(), tee(), or | ||
| // values() in the constructor body after super() will materialize the | ||
| // controller before the subclass constructor finishes. Passing a source | ||
| // (for example to install start/pull) leaves the empty-argument path | ||
| // and creates the controller during super() as usual. | ||
| function ensureEmptyDefaultController(stream) { | ||
Member There was a problem hiding this comment. Is this correctly handled in subclasses? A subclass could end up calling cancel, getReader, etc before the constructor finishes, causing the controller to be materialized. Worth documenting and tests. Contributor There was a problem hiding this comment. Looks okay to me? As explained in anonrig's previous comment, the controller is materialized in all those methods:
Subclasses don't really affect this: if a subclass wanted to get access to the controller, they'd still need to pass a | ||
| if (stream[kState].controller !== undefined) | ||
| return stream[kState].controller; | ||
| const controller = new ReadableStreamDefaultController(kSkipThrow); | ||
| controller[kState] = { | ||
| cancelAlgorithm: nonOpCancel, | ||
| closeRequested: false, | ||
| highWaterMark: 1, | ||
| pullAgain: false, | ||
| pullAlgorithm: nonOpCallback, | ||
| pulling: false, | ||
| pullFulfilled: undefined, | ||
| pullRejected: undefined, | ||
| queue: kEmptyQueue, | ||
| queueTotalSize: 0, | ||
| started: true, | ||
| sizeAlgorithm: defaultSizeAlgorithm, | ||
| stream, | ||
| }; | ||
| stream[kState].controller = controller; | ||
| return controller; | ||
| } | ||
| function setupReadableStreamDefaultController( | ||
| stream, | ||
| controller, | ||
| @@ -2824,8 +2885,7 @@ function setupReadableStreamDefaultController( | ||
| const startResult = startAlgorithm(); | ||
| if (isNonThenable(startResult)) { | ||
| // Non-thenable start result: fulfillment is guaranteed and no .then | ||
| // lookup on the result is observable, so run the post-start step | ||
| // directly at the exact microtask position the promise reaction | ||
| @@ -3708,8 +3768,7 @@ function setupReadableByteStreamController( | ||
| const startResult = startAlgorithm(); | ||
| if (isNonThenable(startResult)) { | ||
| // See setupReadableStreamDefaultController. | ||
| queueMicrotask(() => { | ||
| controller[kState].started = true; | ||
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