RetryPolicy

class RetryPolicy

Policy that will render decisions on whether or not to attempt to retry a failed IO.

Constructors

RetryPolicy()

RetryPolicy(RetryDecision Function(RetryStatus) decideOn)

Implementation

RetryPolicy(this.decideOn);

RetryPolicy.alwaysGiveUp() factory

factory RetryPolicy.alwaysGiveUp()

Creates a new policy that will alway decide to give up.

Implementation

factory RetryPolicy.alwaysGiveUp() => RetryPolicy((_) => RetryDecision.giveUp());

RetryPolicy.constantDelay() factory

factory RetryPolicy.constantDelay(Duration delay)

Creates a new policy that will always decide to retry an operation after waiting for the given Duration.

Implementation

factory RetryPolicy.constantDelay(Duration delay) =>
    RetryPolicy((status) => RetryDecision.delayAndRetry(delay));

RetryPolicy.exponentialBackoff() factory

factory RetryPolicy.exponentialBackoff(Duration baseDelay)

Creates a new policy that will always decide to retry an operation, while increasing the delay between attempts exponentially, starting with a delay of baseDelay.

Implementation

factory RetryPolicy.exponentialBackoff(Duration baseDelay) => RetryPolicy(
  (status) => RetryDecision.delayAndRetry(
    _safeMultiply(baseDelay, BigInt.from(2).pow(status.retriesSoFar)),
  ),
);

RetryPolicy.fullJitter() factory

factory RetryPolicy.fullJitter(Duration baseDelay)

Creates a new policy that will always decide to retry an operation using the algorithm described here to determine the delay between each retry.

Implementation

factory RetryPolicy.fullJitter(Duration baseDelay) => RetryPolicy((status) {
  final maxDelay = _safeMultiply(baseDelay, BigInt.from(2).pow(status.retriesSoFar));
  return RetryDecision.delayAndRetry(maxDelay * math.Random().nextDouble());
});

RetryPolicy.limitRetries() factory

factory RetryPolicy.limitRetries(int maxRetries)

Creates a new policy that will decide to retry an operation until maxRetries attempts have already been made, then deciding to give up.

Implementation

factory RetryPolicy.limitRetries(int maxRetries) => RetryPolicy((status) {
  if (status.retriesSoFar >= maxRetries) {
    return RetryDecision.giveUp();
  } else {
    return RetryDecision.delayAndRetry(Duration.zero);
  }
});

Properties

decideOn final

final RetryDecision Function(RetryStatus) decideOn

Function that that will render a decision on the given RetryStatus.

Implementation

final Function1<RetryStatus, RetryDecision> decideOn;

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

capDelay()

RetryPolicy capDelay(Duration maxDelay)

Limit the delay between any 2 retry attempts to maxDelay.

Implementation

RetryPolicy capDelay(Duration maxDelay) => mapDelay((d) => d > maxDelay ? maxDelay : d);

followedBy()

RetryPolicy followedBy(RetryPolicy policy)

Combine this policy with another policy, giving up if this policy wants to, and if not, following the decision of the other policy.

Implementation

RetryPolicy followedBy(RetryPolicy policy) => RetryPolicy((status) {
  final thisDecision = decideOn(status);

  return thisDecision.isGivingUp ? thisDecision : policy.decideOn(status);
});

giveUpAfterCumulativeDelay()

RetryPolicy giveUpAfterCumulativeDelay(Duration cumulativeDelay)

Limits the total amount of delay during retry(s) that this policy will allow before deciding to give up.

Implementation

RetryPolicy giveUpAfterCumulativeDelay(Duration cumulativeDelay) => RetryPolicy(
  (status) =>
      status.cumulativeDelay >= cumulativeDelay ? RetryDecision.giveUp() : decideOn(status),
);

giveUpAfterDelay()

RetryPolicy giveUpAfterDelay(Duration previousDelay)

Limits the amount of delay between any 2 retry attempts to previousDelay before deciding to give up.

Implementation

RetryPolicy giveUpAfterDelay(Duration previousDelay) => RetryPolicy(
  (status) =>
      status.previousDelay.getOrElse(() => Duration.zero) >= previousDelay
          ? RetryDecision.giveUp()
          : decideOn(status),
);

join()

RetryPolicy join(RetryPolicy policy)

Combine this policy with another policy, giving up when either of the policies want to give up and choosing the maximum of the two delays when both of the schedules want to delay the next retry. The opposite of the meet operation.

Implementation

RetryPolicy join(RetryPolicy policy) => RetryPolicy((status) {
  final thisDecision = decideOn(status);
  final thatDecision = policy.decideOn(status);

  if (thisDecision.isGivingUp || thatDecision.isGivingUp) {
    return RetryDecision.giveUp();
  } else {
    return RetryDecision.delayAndRetry(
      Duration(
        microseconds: math.max(
          thisDecision.delay.inMicroseconds,
          thatDecision.delay.inMicroseconds,
        ),
      ),
    );
  }
});

mapDelay()

RetryPolicy mapDelay(Duration Function(Duration) f)

Applies f to the delay of any decision to eventually retry an operation.

Implementation

RetryPolicy mapDelay(Function1<Duration, Duration> f) => RetryPolicy(
  (status) {
    final decision = decideOn(status);

    if (decision.isGivingUp) {
      return RetryDecision.giveUp();
    } else {
      return RetryDecision.delayAndRetry(f(decision.delay));
    }
  },
);

meet()

RetryPolicy meet(RetryPolicy policy)

Combine this policy with another policy, giving up when both of the policies want to give up and choosing the minimum of the two delays when both of the schedules want to delay the next retry. The opposite of the join operation.

Implementation

RetryPolicy meet(RetryPolicy policy) => RetryPolicy((status) {
  final thisDecision = decideOn(status);
  final thatDecision = policy.decideOn(status);

  if (!thisDecision.isGivingUp && !thatDecision.isGivingUp) {
    return RetryDecision.delayAndRetry(
      Duration(
        microseconds: math.min(
          thisDecision.delay.inMicroseconds,
          thatDecision.delay.inMicroseconds,
        ),
      ),
    );
  } else if (thisDecision.isGivingUp) {
    return thatDecision;
  } else if (thatDecision.isGivingUp) {
    return thisDecision;
  } else {
    return RetryDecision.giveUp();
  }
});

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);