stream: reduce per-chunk work in WHATWG tee and BYOB reads

benchmark/webstreams/tee.js

@@ -0,0 +1,44 @@
+'use strict';
+const common = require('../common.js');
+const { ReadableStream } = require('node:stream/web');
+
+const bench = common.createBenchmark(main, {
+  n: [1e5],
+  type: ['normal', 'bytes'],
+});
+
+async function main({ n, type }) {
+  let i = 0;
+  const source = type === 'bytes' ?
+    {
+      type: 'bytes',
+      pull(controller) {
+        if (i++ < n) controller.enqueue(new Uint8Array(16));
+        else controller.close();
+      },
+    } :
+    {
+      pull(controller) {
+        if (i++ < n) controller.enqueue('a');
+        else controller.close();
+      },
+    };
+
+  const rs = new ReadableStream(source);
+  const [branch1, branch2] = rs.tee();
+  const reader1 = branch1.getReader();
+  const reader2 = branch2.getReader();
+  let reads = 0;
+
+  bench.start();
+  for (;;) {
+    const [result1, result2] = await Promise.all([
+      reader1.read(),
+      reader2.read(),
+    ]);
+    if (result1.done || result2.done) break;
+    reads++;
+  }
+  bench.end(reads);
+  console.assert(reads === n);
+}