Concurrency Concepts

Awaited Values

Multiple async calls can be awaited and then combined with ordinary arithmetic.

Await two calls

base
awaited_values.swift
Replay: real traced execution (multi-file project)
func score(_ value: Int) async -> Int {
    return value + 1
}

let base = 5
let first = await score(base)
let second = await score(base + 2)
let total = first + second
let message = "total=\(total)"

print(message)

func score(_ value: Int) async -> Int {
    return value + 1
}

let base = 2
let first = await score(base)
let second = await score(base + 2)
let total = first + second
let message = "total=\(total)"

print(message)

func score(_ value: Int) async -> Int {
    return value + 1
}

let base = 8
let first = await score(base)
let second = await score(base + 2)
let total = first + second
let message = "total=\(total)"

print(message)

  1. base ← 5

    5let base→ 5 = 5  //@base=2, 86let first = await score(base5)7let second = await score(base + 2)

  2. func score(_ value: Int) async -> Int

    pass 1 of 2
    1func score(_ value5: Int) async -> Int {2    return value5 + 13}

  3. first ← 6

    5let base = 5  //@base=2, 86let first→ 6 = await score(base5)7let second = await score(base5 + 2)8let total = first + second

  4. func score(_ value: Int) async -> Int

    pass 2 of 2
    1func score(_ value7: Int) async -> Int {2    return value7 + 13}

  5. second ← 8, total ← 14, message ← total=14

    6let first = await score(base)7let second→ 8 = await score(base5 + 2)8let total→ 14 = first6 + second89let message→ total=14 = "total=\(total14)"1011print(messagetotal=14)
    outputtotal=14

  1. base ← 2

    5let base→ 2 = 26let first = await score(base2)7let second = await score(base + 2)

  2. func score(_ value: Int) async -> Int

    pass 1 of 2
    1func score(_ value2: Int) async -> Int {2    return value2 + 13}

  3. first ← 3

    5let base = 26let first→ 3 = await score(base2)7let second = await score(base2 + 2)8let total = first + second

  4. func score(_ value: Int) async -> Int

    pass 2 of 2
    1func score(_ value4: Int) async -> Int {2    return value4 + 13}

  5. second ← 5, total ← 8, message ← total=8

    6let first = await score(base)7let second→ 5 = await score(base2 + 2)8let total→ 8 = first3 + second59let message→ total=8 = "total=\(total8)"1011print(messagetotal=8)
    outputtotal=8

  1. base ← 8

    5let base→ 8 = 86let first = await score(base8)7let second = await score(base + 2)

  2. func score(_ value: Int) async -> Int

    pass 1 of 2
    1func score(_ value8: Int) async -> Int {2    return value8 + 13}

  3. first ← 9

    5let base = 86let first→ 9 = await score(base8)7let second = await score(base8 + 2)8let total = first + second

  4. func score(_ value: Int) async -> Int

    pass 2 of 2
    1func score(_ value10: Int) async -> Int {2    return value10 + 13}

  5. second ← 11, total ← 20, message ← total=20

    6let first = await score(base)7let second→ 11 = await score(base8 + 2)8let total→ 20 = first9 + second119let message→ total=20 = "total=\(total20)"1011print(messagetotal=20)
    outputtotal=20
awaited value Awaiting each async call stores normal values that later statements can reuse.