Limiter abstract

abstract class Limiter

A rate limiter that controls the throughput and concurrency of submitted IO jobs.

Jobs are queued and executed according to a minimum interval between dispatches and a maximum concurrency limit. Both parameters can be adjusted at runtime.

Create a limiter with Limiter.start, which returns a Resource that manages the background executor fiber.

Constructors

Limiter()

Limiter()

Properties

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;

maxConcurrent no setter

IO<int> get maxConcurrent

The current maximum number of concurrently running jobs.

Implementation

IO<int> get maxConcurrent;

minInterval no setter

IO<Duration> get minInterval

The current minimum interval between job dispatches.

Implementation

IO<Duration> get minInterval;

pending no setter

IO<int> get pending

The number of jobs currently waiting in the queue.

Implementation

IO<int> get pending;

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

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);

setMaxConcurrent()

IO<Unit> setMaxConcurrent(int newMaxConcurrent)

Sets the maximum concurrency to newMaxConcurrent.

Implementation

IO<Unit> setMaxConcurrent(int newMaxConcurrent);

setMinInterval()

IO<Unit> setMinInterval(Duration newMinInterval)

Sets the minimum interval to newMinInterval.

Implementation

IO<Unit> setMinInterval(Duration newMinInterval);

submit()

IO<A> submit<A>(IO<A> job, {int priority = 0})

Submits job to the limiter's queue for execution.

The job is enqueued with the given priority (higher values are dispatched first; default is 0). Returns an IO that completes with the job's result once it finishes. Cancelling the returned IO cancels the job (removing it from the queue or interrupting it if already running).

Implementation

IO<A> submit<A>(
  IO<A> job, {
  int priority = 0,
});

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();

updateMaxConcurrent()

IO<Unit> updateMaxConcurrent(int Function(int) update)

Atomically updates the maximum concurrency by applying update.

Implementation

IO<Unit> updateMaxConcurrent(Function1<int, int> update);

updateMinInterval()

IO<Unit> updateMinInterval(Duration Function(Duration) update)

Atomically updates the minimum interval by applying update.

Implementation

IO<Unit> updateMinInterval(Function1<Duration, Duration> update);

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);

Static Methods

start()

Resource<Limiter> start(
  Duration minInterval, {
  int? maxConcurrent,
  int? maxQueued,
})

Creates and starts a Limiter as a Resource.

• minInterval: minimum delay between dispatching consecutive jobs.
• maxConcurrent: maximum number of jobs running at once (default: unbounded).
• maxQueued: maximum number of jobs waiting in the queue (default: unbounded). Throws LimitReachedException if exceeded.

The Resource manages the background executor — when released, the executor is cancelled and all pending jobs are abandoned.

Implementation

static Resource<Limiter> start(
  Duration minInterval, {
  int? maxConcurrent,
  int? maxQueued,
}) {
  final maxConcurrent0 = maxConcurrent ?? Integer.maxValue;
  final maxQueued0 = maxQueued ?? Integer.maxValue;

  assert(maxQueued0 > 0, "maxQueued must be > 0, was $maxQueued");
  assert(maxConcurrent0 > 0, "maxConcurrent must be > 0, was $maxConcurrent");

  final resources =
      (
        Resource.eval(Queue.create<IO<Unit>>(maxQueued0)),
        Resource.eval(Barrier.create(maxConcurrent0)),
        Resource.eval(Timer.create(minInterval)),
        Supervisor.create(),
      ).tupled;

  return resources.flatMapN((queue, barrier, timer, supervisor) {
    final limiter = LimiterImpl(queue, barrier, timer, supervisor);

    IO<Unit> executor() {
      IO<Unit> go(IO<Unit> fa) {
        &#47;&#47; IO.unit to make sure we exit the barrier even if fa is canceled before getting executed
        final job = IO.unit.productR(fa).guarantee(barrier.exit());

        return supervisor
            .supervise(job)
            .productR(timer.sleep)
            .productR(barrier.enter())
            .productR(queue.dequeue().flatMap(go));
      }

      return barrier.enter().productR(queue.dequeue().flatMap(go));
    }

    return executor().background().as(limiter);
  });
}