At the heart of data processing, event-sourcing, actors, and much more is the queue—a data structure that allows producers to pass work to consumers in a flexible way. On the JVM, most libraries, including Akka, are powered by Java concurrent queues, which are reliable but were designed in a different era, for synchronous (blocking) procedural code. In this presentation, John A. De Goes—architect of the Scalaz 8 effect system—introduces IOQueue, a new type of queue powered by the Scalaz 8 IO monad. IOQueue never blocks and provides seamless, composable back-pressure across an entire application, without users having to think about the problem or write any special code. John will discuss how IOQueue achieves these remarkable properties, and show how the structure can be used to solve hard problems with just a few lines of type-safe, leak-free, composable Scala code. Come learn about the power of Scalaz to solve the hard problems of software development, in a principled way, without compromises.

1. ZIO Queue John A. De Goes — @jdegoes - http://degoes.net ScalaWave 2018
ZIO Queue
ScalaWave 2018 - Gdańsk, Poland
John A. De Goes
@jdegoes - http://degoes.net

2. What is ZIO?
Powered by Queues
Troubled Queues
Introducing ZIO Queue
Wrap Up

3. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
ZIO
ZIO lets you build
high-performance, type-safe,
concurrent, asynchronous
applications that don’t leak
resources or deadlock, and are
easy to reason about
compositionally, test, and refactor.

4. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
github.com/scalaz/scalaz-zio
ZIO

5. def main: Unit = {
println("Hello, what is your name?")
val name = readLine()
println(s"Good morning, $name!")
}
Second-Class Effects
✗ Pass to functions
✗ Return from functions
✗ Store in data structures
✗ Async/sync/concurrency
✓ Resource-safety
What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

6. def main: IO[IOException, Unit] = for {
_ <- putStrLn("Hello, what is your name?")
name <- getStrLn
_ <- putStrLn(s"Good morning, $name!")
} yield ()
First-Class Effects
✓ Pass to functions
✓ Return from functions
✓ Store in data structures
✓ Async/sync/concurrency
✓ Resource-safety
What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

7. IO[E, A]
IO[E, A] is an immutable value that
describes an effectful computation,
which may fail with a value of type E, or
compute a value of type A.
What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

8. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

9. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

10. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

11. def runInParallel[E, A, B](
leftIO : IO[E, A],
rightIO: IO[E, B]): IO[E, (A, B)] =
for {
leftFiber <- leftIO.fork
rightFiber <- rightIO.fork
a <- leftFiber.join
b <- rightFiber.join
} yield (a, b)
Fork/Join Concurrency with Fibers
✓ Massive scalability over threads
✓ Non-blocking
✓ Automatically interruptible
✓ Always resource-safe
✓ Powerful composition
What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up

12. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Powered by Queues

13. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Producer Consumer
offer take
Queue
1-to-1

14. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Producer
Consumer
offer take
Queue
Producer
n-to-1

15. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Producer
Consumer
offer take
Queue
Consumer
1-to-m

16. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Consumer
offer take
Queue
Consumer
Producer
Producer
n-to-m

17. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
FIFO
LIFO
PRIO
Bounded
Unbounded
Dropping
Sliding
dimensions of variation

18. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
queue
actors
send

19. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
concurrent graph search

20. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
resource sharing
scarce resource
e.g. threads
Thread 1
take Thread 2offer

21. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
loose coupling
offer
take
Fast Producers
Slow Consumers
buffer

22. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Troubled Queues

23. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue

24. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
trait BlockingQueue[A] {
def take: A
def offer(a: A): Boolean
}

25. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
Blocks one thread
until element added
trait BlockingQueue[A] {
def take: A
def offer(a: A): Boolean
}

26. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
Fast Producer Slow Consumer
offer take
Queue

27. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
Fast Producer Slow Consumer
offer
take
Queue
manual
backpressure

28. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
def fastProducer = {
if (!queue.offer(a)) {
// Slow down!!!
} else {
// Keep producing...
}
}

29. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.BlockingQueue
Fast Producer Slow Consumer
offer
take
Queue
manual
backpressure
manual
backpressure
take

30. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.ConcurrentLinkedQueue
trait ConcurrentLinkedQueue[A] {
def poll: A
def offer(a: A): Boolean
}
Returns null if empty

31. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
java.util.concurrent.ConcurrentLinkedQueue
Fast Producer Slow Consumer
offer poll
Queue

32. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
github.com/scalaz/scalaz-zio
ZIO QUEUE

33. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
ZIO Queue
trait Queue[A] {
def take: IO[Nothing, A]
def offer(a: A): IO[Nothing, Unit]
def shutdown(ts: Throwable*): IO[Nothing, Unit]
}
object Queue {
def bounded[A](capacity: Int): IO[Nothing, Queue[A]] = ???
def unbounded[A]: IO[Nothing, Queue[A]] = ???
}

34. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Example
for {
queue <- Queue.unbounded[String]
_ <- queue.offer("Give me Coffee!").forever.fork
_ <- queue.take.flatMap(putStrLn).forever
} yield ()

35. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
5. Concurrent
Consumer
offer take
Queue
Consumer
Producer
Producer
ZIO

36. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
4. Interruptible
for {
queue <- Queue.unbounded[String]
fiber <- queue.offer("Give me Coffee!").forever.fork
_ <- fiber.interrupt
} yield ()

37. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
3. Clean Shutdown
for {
queue <- Queue.unbounded[String]
fiber1 <- queue.offer("Give me Coffee!").forever.fork
fiber2 <- queue.take.forever.fork
_ <- queue.shutdown
} yield ()

38. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
2. Asynchronous
for {
queue <- Queue.unbounded[String]
worker = queue.take.flatMap(putStrLn).forever
workers10k = List.fill(10000)(worker)
_ <- IO.forkAll(workers10k)
_ <- queue.offer("More Coffee!").forever.fork
} yield ()

39. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
2. Asynchronous
trait BlockingQueue[A] {
def take: A ;
def offer(a: A): Boolean
}

40. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
1. Composable Backpressure
for {
queue <- Queue.bounded[String](10)
worker = queue.offer("Coffee").forever
workers10k = List.fill(10000)(worker)
_ <- IO.forkAll(workers10k)
_ <- queue.take.flatMap(putStrLn).forever.fork
} yield ()

41. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
case class Actor[+E, -A, +B](run: A => IO[E, B]) { self =>
def ! (a: A): IO[E, B] = run(a)
}

42. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

43. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

44. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

45. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

46. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

47. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

48. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

49. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

50. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

51. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

52. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

53. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeActor[S, E, A, B](supervisor: Supervisor)(s: S)(receive: (S, A) => IO[E, (S, B)]):
IO[Nothing, Actor[E, A, B]] =
for {
state <- Ref(s)
queue <- Queue.bounded[(A, Promise[E, B])](QueueSize)
fiber <- (for {
t <- queue.take
s <- state.get
(a, promise) = t
receiver = receive(s, a)
completer = (s: S, b: B) =>
state.set(s) *> promise.complete(b)
_ <- receiver.redeem(
e => supervise(receiver, e)
.redeem(promise.error, completer), completer)
} yield ()).forever.fork
} yield Actor[E, A, B]((a: A) =>
Promise.make[E, B].flatMap(p => queue.offer((a, p)).flatMap(_ => p.get))

54. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Application: Scalaz Actors
def makeCounter: IO[Nothing, Actor[Nothing, Int, Int]] =
makeActor(Supervisor.logDefects(Logging))(0) {
(state: Int, n: Int) =>
IO.now((state + n, state + n))
}
for {
counter <- makeCounter
_ <- counter ! 40
_ <- counter ! -2
v <- counter ! 0
} yield v

55. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
WRAP UP

56. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
github.com/scalaz/scalaz-zio
ZIO CFC

57. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
ZIO ROADMAP
Performance Sliding Dropping

58. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
https://gitter.im/scalaz/scalaz/
https://gitter.im/scalaz/scalaz-ioqueue/

59. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
Functional Scala by John A. De Goes
Local Remote Date
Scotland European Time Sep 10 - 14
Toronto East Coast Time Oct 1 - 5
? European Time Oct 22 - 26
SF / SV Pacific Coast Time Nov 18 -
22

60. What is ZIO? Powered by Queues Troubled Queues Introducing ZIO Queue Wrap Up
THANK YOU!
@jdegoes - http://degoes.net