trait ConsumerF[F[_], E, A] extends Serializable
A simple interface that models the consumer side of a producer-consumer communication channel.
Currently exposed by ConcurrentChannel.consume.
- F
is effect type used for processing tasks asynchronously
- E
is the type for the completion event
- A
is the type for the stream of events being consumed
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abstract
def
pull: F[Either[E, A]]
Pulls one message from the communication channel, when it becomes available.
Pulls one message from the communication channel, when it becomes available.
Example:
import cats.implicits._ import cats.effect.Async def sum[F[_]](channel: ConsumerF[F, Int, Int], acc: Long = 0) (implicit F: Async[F]): F[Long] = { channel.pull.flatMap { case Left(e) => F.pure(acc + e) case Right(i) => sum(channel, acc + i) } }
- returns
either
Left(e)
, if the channel was closed with a finale
completion event, orRight(a)
, representing a message that was pulled from the channel
-
abstract
def
pullMany(minLength: Int, maxLength: Int): F[Either[E, Seq[A]]]
Pulls a whole batch of messages from the channel, at least one, the returned sequence being no larger than the specified
maxLength
.Pulls a whole batch of messages from the channel, at least one, the returned sequence being no larger than the specified
maxLength
.import cats.implicits._ import cats.effect.Async def sum[F[_]](channel: ConsumerF[F, Int, Int], acc: Long = 0) (implicit F: Async[F]): F[Long] = { channel.pullMany(1, 16).flatMap { case Left(e) => F.pure(acc + e) case Right(seq) => sum(channel, acc + seq.sum) } }
- minLength
is the minimum size of the returned sequence; for as long as the channel isn't halted, the returned task will back-pressure until the required number of events have been collected
- maxLength
is the maximum size of the returned sequence; for fairness purposes (e.g. multiple workers consuming from the same
ConsumerF
), a smaller value is recommended, or otherwiseInt.MaxValue
can be used- returns
either
Left(e)
, if the channel was closed with a finale
completion event, orRight(seq)
, representing a non-empty sequence of messages pulled from the channel, but that is no larger thanmaxLength
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