A simple code for run with retry and concurrently in dart.

executor_concurrently.dart

import 'dart:async';
import 'dart:collection';

FutureOr<T?> executeWithRetry<T>(
  FutureOr<T?> Function() function, {
  int maxRetries = 3,
  int delayFactor = 2, // in seconds
  throwIfFailed = true,
}) async {
  int retries = 0;
  while (retries < maxRetries) {
    try {
      return await function();
    } catch (e) {
      await Future.delayed(Duration(seconds: retries * delayFactor));
      retries++;
      if (retries == maxRetries) {
        if (throwIfFailed) {
          rethrow;
        }
      }
    }
  }

  // nothing to return
  return null;
}

Future<void> runConcurrently(
  List<Function> functions, {
  int maxTasks = 4,
  int maxRetries = 1,
  int delayFactor = 0, // in seconds
  bool throwIfFailed = true,
}) async {
  final queue = Queue<FutureOr<void> Function()>.from(functions);
  final futures = <Future>[];

  while (queue.isNotEmpty) {
    final tasks = queue.take(maxTasks).toList();
    queue.removeWhere((element) => tasks.contains(element));

    for (final task in tasks) {
      futures.add(Future(() async {
        await executeWithRetry(task,
            maxRetries: maxRetries,
            delayFactor: delayFactor,
            throwIfFailed: throwIfFailed);
      }));
    }

    await Future.wait(futures);
  }
}