timeout method

Stop waiting for this future after timeLimit has passed.

Creates a new timeout future that completes with the same result as this future, the source future, if the source future completes in time.

If the source future does not complete before timeLimit has passed, the onTimeout action is executed, and its result (whether it returns or throws) is used as the result of the timeout future. The onTimeout function must return a T or a Future<T>. If onTimeout returns a future, the alternative result future, the eventual result of the alternative result future is used to complete the timeout future, even if the source future completes before the alternative result future. It only matters that the source future did not complete in time.

If onTimeout is omitted, a timeout will cause the returned future to complete with a TimeoutException.

In either case, the source future can still complete normally at a later time. It just won't be used as the result of the timeout future unless it completes within the time bound. Even if the source future completes with an error, if that error happens after timeLimit has passed, the error is ignored, just like a value result would be.

Examples:

void main() async {
  var result =
      await waitTask("completed").timeout(const Duration(seconds: 10));
  print(result); // Prints "completed" after 5 seconds.

  result = await waitTask("completed")
      .timeout(const Duration(seconds: 1), onTimeout: () => "timeout");
  print(result); // Prints "timeout" after 1 second.

  result = await waitTask("first").timeout(const Duration(seconds: 2),
      onTimeout: () => waitTask("second"));
  print(result); // Prints "second" after 7 seconds.

  try {
    await waitTask("completed").timeout(const Duration(seconds: 2));
  } on TimeoutException {
    print("throws"); // Prints "throws" after 2 seconds.
  }

  var printFuture = waitPrint();
  await printFuture.timeout(const Duration(seconds: 2), onTimeout: () {
    print("timeout"); // Prints "timeout" after 2 seconds.
  });
  await printFuture; // Prints "printed" after additional 3 seconds.

  try {
    await waitThrow("error").timeout(const Duration(seconds: 2));
  } on TimeoutException {
    print("throws"); // Prints "throws" after 2 seconds.
  }
  // StateError is ignored
}

/// Returns [string] after five seconds.
Future<String> waitTask(String string) async {
  await Future.delayed(const Duration(seconds: 5));
  return string;
}

/// Prints "printed" after five seconds.
Future<void> waitPrint() async {
  await Future.delayed(const Duration(seconds: 5));
  print("printed");
}
/// Throws a [StateError] with [message] after five seconds.
Future<void> waitThrow(String message) async {
  await Future.delayed(const Duration(seconds: 5));
  throw Exception(message);
}

Implementation

DoneFuture mixin