stream: cut per-chunk overhead in WHATWG streams

mcollina · aduh95 · commit c81f894ebe01 · 2026-07-06T10:03:32.000+02:00
Consolidate the spec's per-chunk predicate chains (CanCloseOrEnqueue, IsLocked, HasDefaultReader, GetNumReadRequests, GetDesiredSize and the writable-side equivalents) into single passes over the controller and stream state, mirror "close queued or in flight" as a boolean flag maintained at the few close-request transition sites, and materialize the TransformStream [[backpressureChangePromise]] record lazily on first observation so backpressure flips nobody is waiting on allocate nothing. Assisted-by: Claude Code Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #64252 Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Filip Skokan <panva.ip@gmail.com>
diff --git a/lib/internal/webstreams/readablestream.js b/lib/internal/webstreams/readablestream.js
@@ -2480,21 +2480,26 @@ function readableStreamDefaultControllerClose(controller) {
 }
 
 function readableStreamDefaultControllerEnqueue(controller, chunk) {
-  if (!readableStreamDefaultControllerCanCloseOrEnqueue(controller))
+  // Equivalent to readableStreamDefaultControllerCanCloseOrEnqueue()
+  // followed by isReadableStreamLocked() and
+  // readableStreamGetNumReadRequests(), but with the state loaded once:
+  // this runs for every enqueued chunk.
+  const controllerState = controller[kState];
+  const stream = controllerState.stream;
+  if (controllerState.closeRequested || stream[kState].state !== 'readable')
     return;
 
-  const {
-    stream,
-  } = controller[kState];
-
-  if (isReadableStreamLocked(stream) &&
-      readableStreamGetNumReadRequests(stream)) {
+  const reader = stream[kState].reader;
+  if (reader !== undefined &&
+      reader[kState] !== undefined &&
+      reader[kType] === 'ReadableStreamDefaultReader' &&
+      reader[kState].readRequests.length) {
     readableStreamFulfillReadRequest(stream, chunk, false);
   } else {
     try {
       const chunkSize =
         FunctionPrototypeCall(
-          controller[kState].sizeAlgorithm,
+          controllerState.sizeAlgorithm,
           undefined,
           chunk);
       enqueueValueWithSize(controller, chunk, chunkSize);
@@ -2533,22 +2538,27 @@ function readableStreamDefaultControllerGetDesiredSize(controller) {
 }
 
 function readableStreamDefaultControllerShouldCallPull(controller) {
-  const {
-    stream,
-  } = controller[kState];
-  if (!readableStreamDefaultControllerCanCloseOrEnqueue(controller) ||
-      !controller[kState].started)
+  // Single-pass version of the spec's predicate chain (CanCloseOrEnqueue,
+  // IsLocked, HasDefaultReader, GetNumReadRequests, GetDesiredSize): this
+  // runs at least once per chunk on every default-stream path. The
+  // desired-size computation is inlined because the stream state is
+  // already known to be 'readable' here.
+  const controllerState = controller[kState];
+  const stream = controllerState.stream;
+  if (controllerState.closeRequested ||
+      stream[kState].state !== 'readable' ||
+      !controllerState.started)
     return false;
 
-  if (isReadableStreamLocked(stream) &&
-      readableStreamGetNumReadRequests(stream)) {
+  const reader = stream[kState].reader;
+  if (reader !== undefined &&
+      reader[kState] !== undefined &&
+      reader[kType] === 'ReadableStreamDefaultReader' &&
+      reader[kState].readRequests.length) {
     return true;
   }
 
-  const desiredSize = readableStreamDefaultControllerGetDesiredSize(controller);
-  assert(desiredSize !== null);
-
-  return desiredSize > 0;
+  return controllerState.highWaterMark - controllerState.queueTotalSize > 0;
 }
 
 function readableStreamDefaultControllerCallPullIfNeeded(controller) {
@@ -2798,28 +2808,29 @@ function readableByteStreamControllerGetDesiredSize(controller) {
 }
 
 function readableByteStreamControllerShouldCallPull(controller) {
-  const {
-    stream,
-  } = controller[kState];
+  // Single-pass version of the spec's predicate chain (HasDefaultReader,
+  // GetNumReadRequests, HasBYOBReader, GetNumReadIntoRequests,
+  // GetDesiredSize): this runs at least once per chunk on every byte
+  // stream path. The desired-size computation is inlined because the
+  // stream state is already known to be 'readable' here.
+  const controllerState = controller[kState];
+  const stream = controllerState.stream;
   if (stream[kState].state !== 'readable' ||
-      controller[kState].closeRequested ||
-      !controller[kState].started) {
+      controllerState.closeRequested ||
+      !controllerState.started) {
     return false;
   }
-  if (readableStreamHasDefaultReader(stream) &&
-      readableStreamGetNumReadRequests(stream) > 0) {
-    return true;
-  }
-
-  if (readableStreamHasBYOBReader(stream) &&
-      readableStreamGetNumReadIntoRequests(stream) > 0) {
-    return true;
+  const reader = stream[kState].reader;
+  if (reader !== undefined && reader[kState] !== undefined) {
+    const type = reader[kType];
+    if (type === 'ReadableStreamDefaultReader') {
+      if (reader[kState].readRequests.length) return true;
+    } else if (type === 'ReadableStreamBYOBReader') {
+      if (reader[kState].readIntoRequests.length) return true;
+    }
   }
 
-  const desiredSize = readableByteStreamControllerGetDesiredSize(controller);
-  assert(desiredSize !== null);
-
-  return desiredSize > 0;
+  return controllerState.highWaterMark - controllerState.queueTotalSize > 0;
 }
 
 function readableByteStreamControllerHandleQueueDrain(controller) {
diff --git a/lib/internal/webstreams/transformstream.js b/lib/internal/webstreams/transformstream.js
@@ -258,12 +258,7 @@ function InternalTransferredTransformStream() {
     readable: undefined,
     writable: undefined,
     backpressure: undefined,
-    backpressureChange: {
-      __proto__: null,
-      promise: undefined,
-      resolve: undefined,
-      reject: undefined,
-    },
+    backpressureChange: undefined,
     controller: undefined,
   };
 }
@@ -390,12 +385,7 @@ function initializeTransformStream(
     writable,
     controller: undefined,
     backpressure: undefined,
-    backpressureChange: {
-      __proto__: null,
-      promise: undefined,
-      resolve: undefined,
-      reject: undefined,
-    },
+    backpressureChange: undefined,
   };
 
   transformStreamSetBackpressure(stream, true);
@@ -429,12 +419,27 @@ function transformStreamUnblockWrite(stream) {
     transformStreamSetBackpressure(stream, false);
 }
 
+// The spec's [[backpressureChangePromise]] is only ever observed by the
+// source pull algorithm (settles when backpressure next becomes true) and
+// by a sink write arriving while backpressure is set (settles when
+// backpressure next becomes false). Instead of allocating a fresh promise
+// record on every flip, the record is materialized lazily on first
+// observation and dropped once settled; flips nobody is waiting on
+// allocate nothing.
+function transformStreamBackpressureChangePromise(stream) {
+  const state = stream[kState];
+  return (state.backpressureChange ??= PromiseWithResolvers()).promise;
+}
+
 function transformStreamSetBackpressure(stream, backpressure) {
-  assert(stream[kState].backpressure !== backpressure);
-  if (stream[kState].backpressureChange.promise !== undefined)
-    stream[kState].backpressureChange.resolve?.();
-  stream[kState].backpressureChange = PromiseWithResolvers();
-  stream[kState].backpressure = backpressure;
+  const state = stream[kState];
+  assert(state.backpressure !== backpressure);
+  const backpressureChange = state.backpressureChange;
+  if (backpressureChange !== undefined) {
+    state.backpressureChange = undefined;
+    backpressureChange.resolve();
+  }
+  state.backpressure = backpressure;
 }
 
 function setupTransformStreamDefaultController(
@@ -554,7 +559,7 @@ function transformStreamDefaultSinkWriteAlgorithm(stream, chunk) {
   } = stream[kState];
   assert(writable[kState].state === 'writable');
   if (stream[kState].backpressure) {
-    const backpressureChange = stream[kState].backpressureChange.promise;
+    const backpressureChange = transformStreamBackpressureChangePromise(stream);
     return PromisePrototypeThen(
       backpressureChange,
       () => {
@@ -638,9 +643,8 @@ function transformStreamDefaultSinkCloseAlgorithm(stream) {
 
 function transformStreamDefaultSourcePullAlgorithm(stream) {
   assert(stream[kState].backpressure);
-  assert(stream[kState].backpressureChange.promise !== undefined);
   transformStreamSetBackpressure(stream, false);
-  return stream[kState].backpressureChange.promise;
+  return transformStreamBackpressureChangePromise(stream);
 }
 
 function transformStreamDefaultSourceCancelAlgorithm(stream, reason) {
diff --git a/lib/internal/webstreams/util.js b/lib/internal/webstreams/util.js
@@ -134,45 +134,44 @@ function isBrandCheck(brand) {
   };
 }
 
+// The queue helpers below run once per chunk on the hot paths of every
+// default readable/writable stream, so they load the controller state a
+// single time and don't assert the existence of the queue fields (both
+// are unconditionally initialized during controller setup and only ever
+// replaced wholesale).
 function dequeueValue(controller) {
-  assert(controller[kState].queue !== undefined);
-  assert(controller[kState].queueTotalSize !== undefined);
-  assert(controller[kState].queue.length);
+  const state = controller[kState];
+  assert(state.queue.length);
   const {
     value,
     size,
-  } = ArrayPrototypeShift(controller[kState].queue);
-  controller[kState].queueTotalSize =
-    MathMax(0, controller[kState].queueTotalSize - size);
+  } = ArrayPrototypeShift(state.queue);
+  state.queueTotalSize = MathMax(0, state.queueTotalSize - size);
   return value;
 }
 
 function resetQueue(controller) {
-  assert(controller[kState].queue !== undefined);
-  assert(controller[kState].queueTotalSize !== undefined);
-  controller[kState].queue = [];
-  controller[kState].queueTotalSize = 0;
+  const state = controller[kState];
+  state.queue = [];
+  state.queueTotalSize = 0;
 }
 
 function peekQueueValue(controller) {
-  assert(controller[kState].queue !== undefined);
-  assert(controller[kState].queueTotalSize !== undefined);
-  assert(controller[kState].queue.length);
-  return controller[kState].queue[0].value;
+  const state = controller[kState];
+  assert(state.queue.length);
+  return state.queue[0].value;
 }
 
 function enqueueValueWithSize(controller, value, size) {
-  assert(controller[kState].queue !== undefined);
-  assert(controller[kState].queueTotalSize !== undefined);
+  const state = controller[kState];
   const coercedSize = +size;
   if (NumberIsNaN(coercedSize) ||
       coercedSize < 0 ||
       coercedSize === Infinity) {
     throw new ERR_INVALID_ARG_VALUE.RangeError('size', size);
   }
-  size = coercedSize;
-  ArrayPrototypePush(controller[kState].queue, { value, size });
-  controller[kState].queueTotalSize += size;
+  ArrayPrototypePush(state.queue, { value, size: coercedSize });
+  state.queueTotalSize += coercedSize;
 }
 
 // Arity-specialized variants of the promise-callback wrapper. The generic
diff --git a/lib/internal/webstreams/writablestream.js b/lib/internal/webstreams/writablestream.js
