stream: trim webstream setup and teardown work

Short-lived streams (create, a few chunks, close) pay a fixed cost per
stream that dominates once the per-chunk path is lean:

* The queue ring buffer grew after a push filled it, so the initial
  8-slot ring held only three (value, size) pairs and a four-chunk
  stream reallocated every time. Growing before the push lets the ring
  hold four pairs.

* pipeTo observed the source's closed promise with two reactions and,
  on teardown, let the reader and writer release paths probe and reject
  promise records that only the pipe could have observed. One reaction
  pair now watches the source, and finalize drops the records before
  release.

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

lib/internal/webstreams/readablestream.js

@@ -1595,6 +1595,13 @@ function readableStreamPipeTo(
   // tells us that the promise must be rejected even
   // when error is undefine.
   function finalize(rejected, error) {
+    // The pipe is the only observer of the reader's and writer's promise
+    // records (including the ready hook installed by parkOnReady), and
+    // it is done with them: dropping them lets release skip the
+    // pending-promise probes and the rejections nothing would handle.
+    writer[kState].ready = undefined;
+    writer[kState].close = undefined;
+    reader[kState].close = undefined;
     writableStreamDefaultWriterRelease(writer);
     readableStreamReaderGenericRelease(reader);
     if (signal !== undefined)
@@ -1692,12 +1699,6 @@ function readableStreamPipeTo(
       PromisePrototypeThen(promise, undefined, action);
   }
 
-  function watchClosed(stream, promise, action) {
-    if (stream[kState].state === 'closed')
-      action();
-    else
-      PromisePrototypeThen(promise, action, () => {});
-  }
 
   // The pump loop is callback-driven to avoid per-iteration promise
   // allocations. At most one read is in flight at a time, so one read
@@ -1828,15 +1829,34 @@ function readableStreamPipeTo(
 
   pump();
 
-  watchErrored(source, readerClosedPromise(reader).promise, (error) => {
+  function onSourceErrored(error) {
     if (!preventAbort) {
       return shutdownWithAnAction(
         () => writableStreamAbort(dest, error),
         true,
         error);
     }
     shutdown(true, error);
-  });
+  }
+
+  function onSourceClosed() {
+    if (!preventClose) {
+      return shutdownWithAnAction(
+        () => writableStreamDefaultWriterCloseWithErrorPropagation(writer));
+    }
+    shutdown();
+  }
+
+  // The spec installs the source-errored watcher before the dest-errored
+  // one and the source-closed watcher last; a source that is already
+  // errored is handled before the dest watcher is installed, and an
+  // already-closed source after it, as before.
+  if (source[kState].state === 'errored') {
+    onSourceErrored(source[kState].storedError);
+  } else if (source[kState].state !== 'closed') {
+    PromisePrototypeThen(
+      readerClosedPromise(reader).promise, onSourceClosed, onSourceErrored);
+  }
 
   watchErrored(dest, writerClosedPromise(writer).promise, (error) => {
     if (!preventCancel) {
@@ -1848,13 +1868,8 @@ function readableStreamPipeTo(
     shutdown(true, error);
   });
 
-  watchClosed(source, readerClosedPromise(reader).promise, () => {
-    if (!preventClose) {
-      return shutdownWithAnAction(
-        () => writableStreamDefaultWriterCloseWithErrorPropagation(writer));
-    }
-    shutdown();
-  });
+  if (source[kState].state === 'closed')
+    onSourceClosed();
 
   if (writableStreamCloseQueuedOrInFlight(dest) ||
       dest[kState].state === 'closed') {
@@ -2864,29 +2879,27 @@ function setupReadableStreamDefaultController(
 
   const startResult = startAlgorithm();
 
+  const started = () => {
+    controller[kState].started = true;
+    assert(!controller[kState].pulling);
+    assert(!controller[kState].pullAgain);
+    readableStreamDefaultControllerCallPullIfNeeded(controller);
+  };
+
   if (startResult === null ||
       (typeof startResult !== 'object' && typeof startResult !== 'function')) {
     // 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
-    // would have had, skipping two promise allocations.
-    queueMicrotask(() => {
-      controller[kState].started = true;
-      assert(!controller[kState].pulling);
-      assert(!controller[kState].pullAgain);
-      readableStreamDefaultControllerCallPullIfNeeded(controller);
-    });
+    // lookup on the result is observable, so the post-start step runs at
+    // the exact microtask position the promise reaction would have had.
+    queueMicrotask(started);
     return;
   }
 
+  // The wrapper promise matches the reference implementation's
+  // promiseResolvedWith(), whose extra microtask hops WPT relies on.
   PromisePrototypeThen(
     new Promise((r) => r(startResult)),
-    () => {
-      controller[kState].started = true;
-      assert(!controller[kState].pulling);
-      assert(!controller[kState].pullAgain);
-      readableStreamDefaultControllerCallPullIfNeeded(controller);
-    },
+    started,
     (error) => readableStreamDefaultControllerError(controller, error));
 }
 
@@ -3748,26 +3761,23 @@ function setupReadableByteStreamController(
 
   const startResult = startAlgorithm();
 
+  const started = () => {
+    controller[kState].started = true;
+    assert(!controller[kState].pulling);
+    assert(!controller[kState].pullAgain);
+    readableByteStreamControllerCallPullIfNeeded(controller);
+  };
+
+  // See setupReadableStreamDefaultController.
   if (startResult === null ||
       (typeof startResult !== 'object' && typeof startResult !== 'function')) {
-    // See setupReadableStreamDefaultController.
-    queueMicrotask(() => {
-      controller[kState].started = true;
-      assert(!controller[kState].pulling);
-      assert(!controller[kState].pullAgain);
-      readableByteStreamControllerCallPullIfNeeded(controller);
-    });
+    queueMicrotask(started);
     return;
   }
 
   PromisePrototypeThen(
     new Promise((r) => r(startResult)),
-    () => {
-      controller[kState].started = true;
-      assert(!controller[kState].pulling);
-      assert(!controller[kState].pullAgain);
-      readableByteStreamControllerCallPullIfNeeded(controller);
-    },
+    started,
     (error) => readableByteStreamControllerError(controller, error));
 }
 

lib/internal/webstreams/util.js

@@ -179,12 +179,12 @@ class Queue {
   // Single-slot entries (readable byte controller chunk records).
 
   push(entry) {
+    if (this.length === this.list.length)
+      this.grow();
     const tail = this.tail;
     this.list[tail] = entry;
     this.tail = (tail + 1) & this.capacityMask;
     this.length++;
-    if (this.tail === this.head)
-      this.grow();
   }
 
   shift() {
@@ -207,14 +207,14 @@ class Queue {
   // never need to wrap.
 
   pushPair(value, size) {
+    if (this.length * 2 === this.list.length)
+      this.grow();
     const tail = this.tail;
     const list = this.list;
     list[tail] = value;
     list[tail + 1] = size;
     this.tail = (tail + 2) & this.capacityMask;
     this.length++;
-    if (this.tail === this.head)
-      this.grow();
   }
 
   // Returns the dequeued value; the size of the same entry is left in
@@ -237,9 +237,11 @@ class Queue {
     return this.list[this.head];
   }
 
-  // The ring is completely full (the post-push tail caught up with the
-  // head): double the capacity, re-linearizing from the head so index
-  // arithmetic stays trivial.
+  // The ring is completely full (the tail has caught up with the head, so
+  // the next push would overwrite the oldest entry): double the capacity,
+  // re-linearizing from the head so index arithmetic stays trivial.
+  // Growing before the push rather than after it lets the initial 8-slot
+  // ring hold four (value, size) pairs without reallocating.
   grow() {
     const list = this.list;
     const capacity = list.length;

lib/internal/webstreams/writablestream.js

@@ -1379,29 +1379,27 @@ function setupWritableStreamDefaultController(
 
   const startResult = startAlgorithm();
 
+  const started = () => {
+    assert(stream[kState].state === 'writable' ||
+           stream[kState].state === 'erroring');
+    controller[kState].started = true;
+    writableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
+  };
+
   if (startResult === null ||
       (typeof startResult !== 'object' && typeof startResult !== 'function')) {
     // 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
-    // would have had, skipping two promise allocations.
-    queueMicrotask(() => {
-      assert(stream[kState].state === 'writable' ||
-             stream[kState].state === 'erroring');
-      controller[kState].started = true;
-      writableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
-    });
+    // lookup on the result is observable, so the post-start step runs at
+    // the exact microtask position the promise reaction would have had.
+    queueMicrotask(started);
     return;
   }
 
+  // The wrapper promise matches the reference implementation's
+  // promiseResolvedWith(), whose extra microtask hops WPT relies on.
   PromisePrototypeThen(
     new Promise((r) => r(startResult)),
-    () => {
-      assert(stream[kState].state === 'writable' ||
-             stream[kState].state === 'erroring');
-      controller[kState].started = true;
-      writableStreamDefaultControllerAdvanceQueueIfNeeded(controller);
-    },
+    started,
     (error) => {
       assert(stream[kState].state === 'writable' ||
              stream[kState].state === 'erroring');