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Version: 2.0.x

TQueue

A TQueue[A] is a mutable queue that can participate in transactions in STM.

Create a TQueue​

Creating an empty bounded TQueue with specified capacity:

import zio._
import zio.stm._

val tQueueBounded: STM[Nothing, TQueue[Int]] = TQueue.bounded[Int](5)

Creating an empty unbounded TQueue:

import zio._
import zio.stm._

val tQueueUnbounded: STM[Nothing, TQueue[Int]] = TQueue.unbounded[Int]

Put element(s) in a TQueue​

In order to put an element to a TQueue:

import zio._
import zio.stm._

val tQueueOffer: UIO[TQueue[Int]] = (for {
  tQueue <- TQueue.bounded[Int](3)
  _      <- tQueue.offer(1)
} yield tQueue).commit

The specified element will be successfully added to a queue if the queue is not full. It will wait for an empty slot in the queue otherwise.

Alternatively, you can provide a list of elements:

import zio._
import zio.stm._

val tQueueOfferAll: UIO[TQueue[Int]] = (for {
  tQueue <- TQueue.bounded[Int](3)
  _      <- tQueue.offerAll(List(1, 2))
} yield tQueue).commit

Retrieve element(s) from a TQueue​

The first element of the queue can be obtained as follows:

import zio._
import zio.stm._

val tQueueTake: UIO[Int] = (for {
  tQueue <- TQueue.bounded[Int](3)
  _      <- tQueue.offerAll(List(1, 2))
  res    <- tQueue.take
} yield res).commit

In case the queue is empty it will block execution waiting for the element you're asking for.

This behavior can be avoided by using poll method that will return an element if exists or None otherwise:

import zio._
import zio.stm._

val tQueuePoll: UIO[Option[Int]] = (for {
  tQueue <- TQueue.bounded[Int](3)
  res    <- tQueue.poll
} yield res).commit

Retrieving first n elements of the queue:

import zio._
import zio.stm._

val tQueueTakeUpTo: UIO[Chunk[Int]] = (for {
  tQueue <- TQueue.bounded[Int](4)
  _      <- tQueue.offerAll(List(1, 2))
  res    <- tQueue.takeUpTo(3)
} yield res).commit

All elements of the queue can be obtained as follows:

import zio._
import zio.stm._

val tQueueTakeAll: UIO[Chunk[Int]] = (for {
  tQueue <- TQueue.bounded[Int](4)
  _      <- tQueue.offerAll(List(1, 2))
  res    <- tQueue.takeAll
} yield res).commit

Size of a TQueue​

The number of elements in the queue can be obtained as follows:

import zio._
import zio.stm._

val tQueueSize: UIO[Int] = (for {
  tQueue <- TQueue.bounded[Int](3)
  _      <- tQueue.offerAll(List(1, 2))
  size   <- tQueue.size
} yield size).commit