Implementation of Readable iteration helpers that does not rely on Async Iteration

benchmark/streams/operator-throughput.js

@@ -0,0 +1,138 @@
+'use strict';
+
+const assert = require('assert');
+const common = require('../common');
+const { Readable } = require('stream');
+
+const bench = common.createBenchmark(main, {
+  n: [2e5],
+  operation: [
+    'reduce',
+    'reduce-async',
+    'map-sync-1',
+    'map-sync-8',
+    'map-async-1',
+    'map-async-8',
+    'find-sync-1',
+    'find-sync-8',
+    'find-async-1',
+    'find-async-8',
+    'filter',
+    'forEach',
+    'toArray',
+  ],
+  source: ['readable', 'iterator', 'array'],
+});
+
+function createSource(type, n) {
+  if (type === 'array') {
+    return Readable.from(Array.from({ length: n }, (_, i) => i));
+  }
+  let i = 0;
+
+  if (type === 'readable') {
+    return new Readable({
+      objectMode: true,
+      read() {
+        this.push(i === n ? null : i++);
+      },
+    });
+  }
+
+  return Readable.from((function* generate() {
+    while (i < n) {
+      yield i++;
+    }
+  })());
+}
+
+async function main({ n, operation, source }) {
+  const readable = createSource(source, n);
+  let result;
+
+  bench.start();
+
+  switch (operation) {
+    case 'reduce':
+      result = await readable.reduce((sum, value) => sum + value, 0);
+      break;
+    case 'reduce-async':
+      result = await readable.reduce(async (sum, value) => sum + value, 0);
+      break;
+    case 'map-sync-1':
+      result = await readable
+        .map((value) => value + 1, { concurrency: 1 })
+        .reduce((sum, value) => sum + value, 0);
+      break;
+    case 'map-sync-8':
+      result = await readable
+        .map((value) => value + 1, { concurrency: 8 })
+        .reduce((sum, value) => sum + value, 0);
+      break;
+    case 'map-async-1':
+      result = await readable
+        .map(async (value) => value + 1, { concurrency: 1 })
+        .reduce((sum, value) => sum + value, 0);
+      break;
+    case 'map-async-8':
+      result = await readable
+        .map(async (value) => value + 1, { concurrency: 8 })
+        .reduce((sum, value) => sum + value, 0);
+      break;
+    case 'find-sync-1':
+      result = await readable.find((value) => value === n - 1, { concurrency: 1 });
+      break;
+    case 'find-sync-8':
+      result = await readable.find((value) => value === n - 1, { concurrency: 8 });
+      break;
+    case 'find-async-1':
+      result = await readable.find(async (value) => value === n - 1, { concurrency: 1 });
+      break;
+    case 'find-async-8':
+      result = await readable.find(async (value) => value === n - 1, { concurrency: 8 });
+      break;
+    case 'filter':
+      result = await readable
+        .filter((value) => (value & 1) === 0)
+        .reduce((sum, value) => sum + value, 0);
+      break;
+    case 'forEach':
+      result = 0;
+      await readable.forEach((value) => { result += value; });
+      break;
+    case 'toArray':
+      result = await readable.toArray();
+      break;
+    default:
+      throw new Error(`Unknown operation: ${operation}`);
+  }
+
+  bench.end(n);
+
+  const sum = n * (n - 1) / 2;
+  switch (operation) {
+    case 'map-sync-1':
+    case 'map-sync-8':
+    case 'map-async-1':
+    case 'map-async-8':
+      assert.strictEqual(result, sum + n);
+      break;
+    case 'find-sync-1':
+    case 'find-sync-8':
+    case 'find-async-1':
+    case 'find-async-8':
+      assert.strictEqual(result, n - 1);
+      break;
+    case 'filter': {
+      const evenCount = Math.ceil(n / 2);
+      assert.strictEqual(result, evenCount * (evenCount - 1));
+      break;
+    }
+    case 'toArray':
+      assert.strictEqual(result.length, n);
+      assert.strictEqual(result[n - 1], n - 1);
+      break;
+    default:
+      assert.strictEqual(result, sum);
+  }
+}

lib/internal/streams/from.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const {
+  ArrayIsArray,
   PromisePrototypeThen,
   SymbolAsyncIterator,
   SymbolIterator,
@@ -15,6 +16,10 @@ const {
   },
 } = require('internal/errors');
 
+const {
+  getDefaultHighWaterMark,
+} = require('internal/streams/state');
+
 function from(Readable, iterable, opts) {
   let iterator;
   if (typeof iterable === 'string' || iterable instanceof Buffer) {
@@ -26,6 +31,8 @@ function from(Readable, iterable, opts) {
         this.push(null);
       },
     });
+  } else if (iterable instanceof Readable) {
+    return iterable;
   }
 
   let isAsync;
@@ -39,10 +46,9 @@ function from(Readable, iterable, opts) {
     throw new ERR_INVALID_ARG_TYPE('iterable', ['Iterable'], iterable);
   }
 
-
   const readable = new Readable({
     objectMode: true,
-    highWaterMark: 1,
+    highWaterMark: ArrayIsArray(iterable) ? getDefaultHighWaterMark(true) : 1,
     // TODO(ronag): What options should be allowed?
     ...opts,
   });