Impara Simple Retry Patterns | Chaining and Coordination

When you use asynchronous operations in Dart, failures can happen for many reasons, such as network errors or unavailable resources. Retrying a failed operation is a common approach to increase reliability: if the first attempt fails, you simply try again. In its simplest form, a retry mechanism will attempt the operation, and if it throws an error or returns a failed Future, it will run the operation again a fixed number of times or until it succeeds. However, simple retry logic has limitations. It may not distinguish between recoverable and unrecoverable errors, can lead to repeated failures if the underlying problem persists, and can potentially overwhelm resources or external services if not managed carefully. Proper retry strategies often include delays between attempts, a maximum number of retries, and careful error handling to avoid infinite loops or resource exhaustion.

retry_example.dart


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import 'dart:async';
import 'dart:math';

// Simulate an async operation that may fail
Future<String> unreliableOperation() async {
  final random = Random();
  await Future.delayed(Duration(milliseconds: 200));
  if (random.nextBool()) {
    // Simulate failure
    throw Exception('Operation failed!');
  }
  return 'Success!';
}

// Retry the operation once if it fails
Future<String> retryOnce(Future<String> Function() operation) async {
  try {
    return await operation();
  } catch (e) {
    print('First attempt failed: $e');
    try {
      return await operation();
    } catch (e) {
      print('Second attempt failed: $e');
      rethrow;
    }
  }
}

void main() async {
  try {
    final result = await retryOnce(unreliableOperation);
    print('Final result: $result');
  } catch (e) {
    print('Operation ultimately failed: $e');
  }
}

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Sezione 2. Capitolo 4

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retry_example.dart


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import 'dart:async';
import 'dart:math';

// Simulate an async operation that may fail
Future<String> unreliableOperation() async {
  final random = Random();
  await Future.delayed(Duration(milliseconds: 200));
  if (random.nextBool()) {
    // Simulate failure
    throw Exception('Operation failed!');
  }
  return 'Success!';
}

// Retry the operation once if it fails
Future<String> retryOnce(Future<String> Function() operation) async {
  try {
    return await operation();
  } catch (e) {
    print('First attempt failed: $e');
    try {
      return await operation();
    } catch (e) {
      print('Second attempt failed: $e');
      rethrow;
    }
  }
}

void main() async {
  try {
    final result = await retryOnce(unreliableOperation);
    print('Final result: $result');
  } catch (e) {
    print('Operation ultimately failed: $e');
  }
}

Tutto è chiaro?

Grazie per i tuoi commenti!

Sezione 2. Capitolo 4