Concurrent IO

---
class: medium-code

# fromTwoClients

.fifty-two-left[
 
```scala
def searchByClient(client: SearchFlightClient) =
 client
 .search(from, to, date)
 .handleErrorWith(_ => IO(Nil))

for {
 flights1 <- searchByClient(client1)
 flights2 <- searchByClient(client2)
} yield SearchResult(flights1 ++ flights2)
```
]

---
class: medium-code

# fromTwoClients

.fifty-two-left[
 
```scala
def searchByClient(client: SearchFlightClient) =
 `client`
 `.search(from, to, date)`
 .handleErrorWith(_ => IO(Nil))

for {
 flights1 <- searchByClient(client1)
 flights2 <- searchByClient(client2)
} yield SearchResult(flights1 ++ flights2)
```
]

---
class: medium-code

# fromTwoClients

.fifty-two-left[
 
```scala
def searchByClient(client: SearchFlightClient) =
 client
 .search(from, to, date)
 .handleErrorWith(_ => IO(Nil))

for {
 flights1 `<-` searchByClient(client1)
 flights2 `<-` searchByClient(client2)
} yield SearchResult(flights1 ++ flights2)
```
]

---
class: medium-code

# fromTwoClients is sequential

.fifty-two-left[
 
```scala
def searchByClient(client: SearchFlightClient) =
 client
 .search(from, to, date)
 .handleErrorWith(_ => IO(Nil))

for {
 flights1 <- searchByClient(client1)
 flights2 <- searchByClient(client2)
} yield SearchResult(flights1 ++ flights2)
```
]

.forty-seven-right[.center[
 
<img src="../img/foundation/from-two-clients-1.svg" style="width:500px;"/>
]]

---
class: medium-code

# For comprehensions are sequential

.fifty-two-left[
 
```scala
def searchByClient(client: SearchFlightClient) =
 client
 .search(from, to, date)
 .handleErrorWith(_ => IO(Nil))

for {
 `flights1` <- searchByClient(client1)
 flights2 <- `searchByClient(client2)`
} yield SearchResult(flights1 ++ flights2)
```
]

.forty-seven-right[.center[
 
<img src="../img/foundation/from-two-clients-1.svg" style="width:500px;"/>
]]

---
class: medium-code

# map and flatMap are sequential

.fifty-two-left[
 
```scala
searchByClient(client1).flatMap { `flights1` =>
 searchByClient(client2).map { `flights2` =>
 SearchResult(flights1 ++ flights2)
 }
}
```
]

.forty-seven-right[.center[
 
<img src="../img/foundation/from-two-clients-1.svg" style="width:500px;"/>
]]

---
class: medium-code

# Concurrent IOs

// Runs both the current IO and "other" concurrently,
  // then combine their results into a tuple
  def parZip[Other](other: IO[Other])(ec: ExecutionContext): IO[(A, Other)] =
    ???

}
```
]

---
class: medium-code

# Concurrent IOs

// Runs both the current IO and "other" `concurrently`,
  // then combine their results into a tuple
  def parZip[Other](other: IO[Other])(ec: ExecutionContext): IO[(A, Other)] =
    ???

// Runs both the current IO and "other" `sequentially`,
 // then combine their results into a tuple
 def zip[Other](other: IO[Other]): IO[(A, Other)] =
 for {
 first <- this
 second <- other
 } yield (first, second)

}
```
]

---
class: medium-code

# Sequential vs Concurrent

.seventy-two-left[
```scala
def stream(taskName: String, iteration: Int, duration: FiniteDuration) =
  List.range(0, iteration).traverse { n =>
    IO.debug(s"Task $taskName $n") andThen IO.sleep(duration)
  }

val streamA = stream("A", 4, 200.millis)
```
]

.seventy-two-left[
```scala
streamA.unsafeRun()
// Task A 0
// Task A 1
// Task A 2
// Task A 3
```
]

---
class: medium-code

# .hl2[Sequential] vs Concurrent

val streamA = stream("A", 4, 200.millis)
val streamB = stream("B", 3, 300.millis)
```
]

.seventy-two-left[
```scala
streamA.`zip`(streamB).unsafeRun()
// Task A 0
// Task A 1
// Task A 2
// Task A 3
// Task B 0
// Task B 1
// Task B 2
```
]

---
class: medium-code

# .hl2[Sequential] vs Concurrent

val streamA = stream("A", 4, 200.millis)
val streamB = stream("B", 3, 300.millis)
```
]

.seventy-two-left[
```scala
streamA.zip(streamB).unsafeRun()
// Task` A `0
// Task` A `1
// Task` A `2
// Task` A `3
// Task` B `0
// Task` B `1
// Task` B `2
```
]

---
class: medium-code

# Sequential vs .hl2[Concurrent]

val streamA = stream("A", 4, 200.millis)
val streamB = stream("B", 3, 300.millis)
```
]

.seventy-two-left[
```scala
streamA.`parZip`(streamB)(ec).unsafeRun()
// Task A 0
// Task B 0
// Task A 1
// Task B 1
// Task A 2
// Task A 3
// Task B 2
```
]

---
class: medium-code

# Sequential vs .hl2[Concurrent]

val streamA = stream("A", 4, 200.millis)
val streamB = stream("B", 3, 300.millis)
```
]

.seventy-two-left[
```scala
streamA.parZip(streamB)(ec).unsafeRun()
// Task` A `0
// Task` B `0
// Task` A `1
// Task` B `1
// Task` A `2
// Task` A `3
// Task` B `2
```
]

---
class: medium-code

# How to implement parZip?

// Runs both the current IO and "other" concurrently,
  // then combine their results into a tuple
  def parZip[Other](other: IO[Other])(ec: ExecutionContext): IO[(A, Other)] =
    `???`

}
```
]

---
class: medium-code

# Futures

.eighty-two-left[
```scala
trait SearchFlightClient {
  def search(from: Airport, to: Airport, date: LocalDate): `Future`[List[Flight]]
}
```
]

---
class: medium-code

# Concurrent Futures