tests/lib/async/slow_consumer2_test.dart

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

// VMOptions=--old_gen_heap_size=64 --no-background-compilation

library slow_consumer2_test;

import 'dart:async';

import 'package:expect/async_helper.dart';
import 'package:expect/expect.dart';

const int KB = 1024;
const int MB = KB * KB;
const int GB = KB * KB * KB;

class SlowConsumer implements StreamConsumer {
  int receivedCount = 0;
  final int bytesPerSecond;
  final int bufferSize;
  final List bufferedData = [];
  int usedBufferSize = 0;
  late int finalCount;

  SlowConsumer(int this.bytesPerSecond, int this.bufferSize);

  Future consume(Stream stream) {
    return addStream(stream).then((_) => close());
  }

  Future addStream(Stream stream) {
    Completer result = new Completer();
    var subscription;
    subscription = stream.listen(
      (dynamic _data) {
        List<int> data = _data;
        receivedCount += data.length;
        usedBufferSize += data.length;
        bufferedData.add(data);
        int currentBufferedDataLength = bufferedData.length;
        if (usedBufferSize > bufferSize) {
          subscription.pause();
          usedBufferSize = 0;
          int ms = data.length * 1000 ~/ bytesPerSecond;
          Duration duration = new Duration(milliseconds: ms);
          new Timer(duration, () {
            for (int i = 0; i < currentBufferedDataLength; i++) {
              bufferedData[i] = null;
            }
            subscription.resume();
          });
        }
      },
      onDone: () {
        finalCount = receivedCount;
        result.complete(receivedCount);
      },
    );
    return result.future;
  }

  Future close() {
    return new Future.value(finalCount);
  }
}

class DataProvider {
  final int chunkSize;
  final int bytesPerSecond;
  int sentCount = 0;
  int targetCount;
  late StreamController controller;

  DataProvider(int this.bytesPerSecond, int this.targetCount, this.chunkSize) {
    controller = new StreamController(
      sync: true,
      onPause: onPauseStateChange,
      onResume: onPauseStateChange,
    );
    Timer.run(send);
  }

  Stream get stream => controller.stream;

  send() {
    if (controller.isPaused) return;
    if (sentCount == targetCount) {
      controller.close();
      return;
    }
    int listSize = chunkSize;
    sentCount += listSize;
    if (sentCount > targetCount) {
      listSize -= sentCount - targetCount;
      sentCount = targetCount;
    }
    controller.add(List.filled(listSize, -1));
    int ms = listSize * 1000 ~/ bytesPerSecond;
    Duration duration = new Duration(milliseconds: ms);
    if (!controller.isPaused) new Timer(duration, send);
  }

  onPauseStateChange() {
    // We don't care if we just unpaused or paused. In either case we just
    // call send which will test it for us.
    send();
  }
}

main() {
  asyncStart();
  // The data provider can deliver 800MB/s of data. It sends 100MB of data to
  // the slower consumer who can only read 200MB/s. The data is sent in 1MB
  // chunks. The consumer has a buffer of 5MB. That is, it can accept a few
  // packages without pausing its input.
  //
  // This test is limited to 32MB of heap-space (see VMOptions on top of the
  // file). If the consumer doesn't pause the data-provider it will run out of
  // heap-space.

  new DataProvider(
    800 * MB,
    100 * MB,
    1 * MB,
  ).stream.pipe(new SlowConsumer(200 * MB, 5 * MB)).then((count) {
    Expect.equals(100 * MB, count);
    asyncEnd();
  });
}