throttled_foreach.dart

import 'dart:async';
import 'dart:io';

import 'dart:math';

StreamController<int> controller = StreamController();

Future<void> main() async {
  final paths = [for (var i = 0; i < 100; i++) "path $i"];

  paths.iterator.throttledForEach(10, (path) async {
    final script = ["-c", "sleep ${Random().nextInt(10)}"];
    final process = await Process.start("sh", script);
    final returnCode = await process.exitCode;
    print("finshed $path with return code $returnCode");
  });
}

extension on Iterator {
  void throttledForEach(int parallelFutures, Function onData) async {
    final semaphores = StreamController<int>();
    while (parallelFutures-- > 0) {
      semaphores.add(1);
    }
    await for (var _ in semaphores.stream) {
      if (!moveNext()) break;
      try {
        onData(current);
      } catch (_) {} finally {
        semaphores.add(1);
      }
    }
  }
}