Ribs

Appearance

ribs_effect›Classes›Queue<A>

Queue<A> abstract ​

abstract class Queue<A>

A concurrent, fiber-safe FIFO queue.

Queue provides asynchronous, back-pressured communication between fibers. Producers offer elements and consumers take them. When the queue is full, producers block; when empty, consumers block.

Several variants are available:

Implementers

Constructors ​

Queue() ​

Queue()

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
dart
external int get hashCode;

runtimeType no setter inherited ​

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation
dart
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:

dart
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:

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

offer() ​

IO<Unit> offer(A a)

Enqueues a, blocking (semantically) if the queue is full.

Implementation
dart
IO<Unit> offer(A a);

size() ​

IO<int> size()

Returns the current number of elements in the queue.

Implementation
dart
IO<int> size();

take() ​

IO<A> take()

Dequeues the next element, blocking (semantically) if the queue is empty.

Implementation
dart
IO<A> take();

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
dart
external String toString();

tryOffer() ​

IO<bool> tryOffer(A a)

Attempts to enqueue a without blocking.

Returns true if the element was enqueued, false otherwise.

Implementation
dart
IO<bool> tryOffer(A a);

tryOfferN() ​

IO<IList<A>> tryOfferN(IList<A> list)

Attempts to enqueue each element of list in order.

Returns the suffix of elements that could not be enqueued.

Implementation
dart
IO<IList<A>> tryOfferN(IList<A> list) => list.uncons(
  (hdtl) => hdtl.foldN(
    () => IO.pure(list),
    (hd, tl) => tryOffer(hd).ifM(() => tryOfferN(tl), () => IO.pure(list)),
  ),
);

tryTake() ​

IO<Option<A>> tryTake()

Attempts to dequeue an element without blocking.

Returns Some with the element, or None if the queue is empty.

Implementation
dart
IO<Option<A>> tryTake();

tryTakeN() ​

IO<IList<A>> tryTakeN(Option<int> maxN)

Attempts to dequeue up to maxN elements without blocking.

If maxN is None, takes all available elements.

Implementation
dart
IO<IList<A>> tryTakeN(Option<int> maxN) {
  return IO.defer(() {
    final limit = maxN.getOrElse(() => Integer.maxValue);
    if (limit <= 0) return IO.pure(nil());

    var count = 0;
    var acc = nil<A>();

    return tryTake()
        .flatMap((oa) {
          return oa.fold(
            () => IO.pure(false),
            (a) {
              acc = acc.prepended(a);
              count++;
              return IO.pure(count < limit);
            },
          );
        })
        .iterateWhile((b) => b)
        .map((_) => acc.reverse());
  });
}

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
dart
external bool operator ==(Object other);

Static Methods ​

bounded() ​

IO<Queue<A>> bounded<A>(int capacity)

Creates a bounded queue with the given capacity.

A capacity of 0 creates a synchronous queue.

Implementation
dart
static IO<Queue<A>> bounded<A>(int capacity) {
  if (capacity == 0) {
    return synchronous();
  } else {
    return Ref.of(_State.empty<A>()).map((s) => _BoundedQueue(capacity, s));
  }
}

circularBuffer() ​

IO<Queue<A>> circularBuffer<A>(int capacity)

Creates a circular buffer queue that overwrites the oldest element when capacity is reached.

Implementation
dart
static IO<Queue<A>> circularBuffer<A>(int capacity) =>
    Ref.of(_State.empty<A>()).map((s) => _CircularBufferQueue(capacity, s));

dropping() ​

IO<Queue<A>> dropping<A>(int capacity)

Creates a dropping queue that silently discards offers when capacity is reached.

Implementation
dart
static IO<Queue<A>> dropping<A>(int capacity) =>
    Ref.of(_State.empty<A>()).map((s) => _DroppingQueue(capacity, s));

synchronous() ​

IO<Queue<A>> synchronous<A>()

Creates a synchronous (zero-capacity) queue where each offer blocks until a corresponding take is ready, and vice versa.

Implementation
dart
static IO<Queue<A>> synchronous<A>() => Ref.of(_SyncState.empty<A>()).map(_SyncQueue.new);

unbounded() ​

IO<Queue<A>> unbounded<A>()

Creates an unbounded queue that never blocks producers.

Implementation
dart
static IO<Queue<A>> unbounded<A>() => bounded(Integer.maxValue);