Non-Blocking IO

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class: center, middle, white

.title[Non-Blocking IO]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
trait IO[A] {

def parZip[Other](other: IO[Other])(ec: ExecutionContext): IO[(A, Other)] =
    IO {
      val future1 = Future {  this.unsafeRun() }(ec)
      val future2 = Future { other.unsafeRun() }(ec)

val combined = future1.zip(future2)

Await.result(combined, Duration.Inf)
    }

}
```
]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
trait IO[A] {

def parZip[Other](other: IO[Other])(ec: ExecutionContext): IO[(A, Other)] =
    IO {
      val future1 = Future {  this.unsafeRun() }(ec)
      val future2 = Future { other.unsafeRun() }(ec)

val combined = future1.zip(future2)

`Await.result`(combined, Duration.Inf)
    }

}
```
]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
trait IO[A] {

def parZip[Other](other: IO[Other])(ec: ExecutionContext): `IO[(A, Other)]` =
    IO {
      val future1 = Future {  this.unsafeRun() }(ec)
      val future2 = Future { other.unsafeRun() }(ec)

val combined = future1.zip(future2)

Await.result(combined, Duration.Inf) : `(A, Other)`
    }

}
```
]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
object IO {

def apply[A](action: => A): `IO[A]` =
    new IO[A] {
      def unsafeRun(): A = action
    }

}
```
]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
object IO {

def apply[A](action: `=> A`): IO[A] =
    new IO[A] {
      def unsafeRun(): A = action
    }

}
```
]

---
class: medium-code

# Why parZip is blocking?

.seventy-seven-left[
```scala
trait IO[A] {

def unsafeRun(): A

}
```
]

---
class: medium-code

# Because unsafeRun is blocking

.seventy-seven-left[
```scala
def block[A](action:     IO[A]): A = action.unsafeRun()

def block[A](future: Future[A]): A = Await.result(future, Duration.Inf)
```
]

---
class: medium-code

# How can we make IO non-blocking?

.seventy-seven-left[
```scala
trait IO[A] {

def unsafeRun(): A

}
```
]

---
class: medium-code

# Future is non-blocking

.sixty-two-left[
```scala
val futureUser = db.getUser(1234)
// futureUser: Future[User] = Future(<not completed>)
```
]

---
class: medium-code

# Future is non-blocking

.sixty-two-left[
```scala
val futureUser = db.getUser(1234)
// futureUser: Future[User] = Future(<not completed>)

val futureName = futureUser.map(_.name)
// futureName: Future[String] = Future(<not completed>)
```
]

---
class: medium-code

# Future is non-blocking

.sixty-two-left[
```scala
trait Future[A] {

def onComplete(callback: Try[A] => Unit): Unit

}
```
]
--

.sixty-two-left[
```scala
db.getUser(1234).onComplete {
  case Failure(error) => println("Oops")
  case Success(user)  => println(s"User 1234 is $user")
}
```
]

---
class: medium-code

# Future is non-blocking

.sixty-two-left[
```scala
trait Future[A] {

def onComplete(callback: Try[A] => Unit): Unit

}
```
]

.sixty-two-left[
```scala
db.getUser(1234).onComplete {
  case Failure(error) => println("Oops")
  case Success(user)  => println(s"User 1234 is $user")
}

db.getUser(4444).onComplete {
  case Failure(error) => println("Oops")
  case Success(user)  => println(s"User 4444 is $user")
}
```
]

---
class: medium-code

# Non-blocking IO

.sixty-two-left[
```scala
trait IO[A] {

def onComplete(callback: Try[A] => Unit): Unit

}
```
]

---
class: medium-code

# Asynchronous IO

.sixty-two-left[
```scala
trait IO[A] {

def unsafeRunAsync(callback: Try[A] => Unit): Unit

}
```
]

---
class: medium-code

# Asynchronous IO

.sixty-two-left[
```scala
trait IO[A] {
  // executes an IO `async`hronously
  def unsafeRunAsync(callback: Try[A] => Unit): Unit

// executes an IO `sync`hronously
  def unsafeRun(): A
}
```
]