Concurrency Basics

Worker Sequence

A single worker goroutine processes queued jobs in send order.

worker A worker reads jobs from a channel and writes results to another channel.

Worker Sequence

extraJob
worker_sequence.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var extraJob = 3
	jobs := make(chan int, 3)
	results := make(chan int, 3)

	go func() {
		for job := range jobs {
			results <- job * 10
		}
	}()

	inputs := []int{1, 2, extraJob}
	for _, job := range inputs {
		jobs <- job
	}
	close(jobs)

	first := <-results
	second := <-results
	third := <-results
	fmt.Println("jobs=", len(inputs))
	fmt.Println("first=", first)
	fmt.Println("second=", second)
	fmt.Println("third=", third)
}

package main

import "fmt"

func main() {
	var extraJob = 4
	jobs := make(chan int, 3)
	results := make(chan int, 3)

	go func() {
		for job := range jobs {
			results <- job * 10
		}
	}()

	inputs := []int{1, 2, extraJob}
	for _, job := range inputs {
		jobs <- job
	}
	close(jobs)

	first := <-results
	second := <-results
	third := <-results
	fmt.Println("jobs=", len(inputs))
	fmt.Println("first=", first)
	fmt.Println("second=", second)
	fmt.Println("third=", third)
}

package main

import "fmt"

func main() {
	var extraJob = 5
	jobs := make(chan int, 3)
	results := make(chan int, 3)

	go func() {
		for job := range jobs {
			results <- job * 10
		}
	}()

	inputs := []int{1, 2, extraJob}
	for _, job := range inputs {
		jobs <- job
	}
	close(jobs)

	first := <-results
	second := <-results
	third := <-results
	fmt.Println("jobs=", len(inputs))
	fmt.Println("first=", first)
	fmt.Println("second=", second)
	fmt.Println("third=", third)
}

  1. extraJob ← 3, jobs ← (chan int)(⟨addr A⟩), results ← (chan int)(⟨addr B⟩)

    5func main() {6  var extraJob→ 3 = 3 //@extraJob=4, 57  jobs→ (chan int)(⟨addr A⟩) := make(chan int, 3)8  results→ (chan int)(⟨addr B⟩) := make(chan int, 3)910  go func() {11    for job := range jobs {12      results <- job * 1013    }14  }()1516  inputs→ []int{1, 2, 3} := []int{1, 2, extraJob3}17  for _, job := range inputs {

  2. for _, job := range inputs

    pass 1 of 3
    16inputs := []int{1, 2, extraJob}17for _, job1 := range inputs[]int{1, 2, 3} {18  jobs(chan int)(⟨addr A⟩) <- job119}
    All 3 passes — pass 1 is the card above
    passjob
    11
    22
    33

  3. close(jobs)

    19}20close(jobs(chan int)(⟨addr A⟩))2122first := <-results(chan int)(⟨addr B⟩)23second := <-results

  4. for job := range jobs

    pass 1 of 3
    10go func() {11  for job1 := range jobs(chan int)(⟨addr A⟩) {12    results(chan int)(⟨addr B⟩) <- job1 * 1013  }
    All 3 passes — pass 1 is the card above
    passjob
    11
    22
    33

  5. first ← 10, second ← 20, third ← 30

    22  first→ 10 := <-results(chan int)(⟨addr B⟩)23  second→ 20 := <-results(chan int)(⟨addr B⟩)24  third→ 30 := <-results(chan int)(⟨addr B⟩)25  fmt.Println("jobs=", len(inputs[]int{1, 2, 3}))26  fmt.Println("first=", first10)27  fmt.Println("second=", second20)28  fmt.Println("third=", third30)29}
    outputjobs= 3
first= 10
second= 20
third= 30

  1. extraJob ← 4, jobs ← (chan int)(⟨addr A⟩), results ← (chan int)(⟨addr B⟩)

    5func main() {6  var extraJob→ 4 = 47  jobs→ (chan int)(⟨addr A⟩) := make(chan int, 3)8  results→ (chan int)(⟨addr B⟩) := make(chan int, 3)910  go func() {11    for job := range jobs {12      results <- job * 1013    }14  }()1516  inputs→ []int{1, 2, 4} := []int{1, 2, extraJob4}17  for _, job := range inputs {

  2. for _, job := range inputs

    pass 1 of 3
    16inputs := []int{1, 2, extraJob}17for _, job1 := range inputs[]int{1, 2, 4} {18  jobs(chan int)(⟨addr A⟩) <- job119}
    All 3 passes — pass 1 is the card above
    passjob
    11
    22
    34

  3. close(jobs)

    19}20close(jobs(chan int)(⟨addr A⟩))2122first := <-results(chan int)(⟨addr B⟩)23second := <-results

  4. for job := range jobs

    pass 1 of 3
    10go func() {11  for job1 := range jobs(chan int)(⟨addr A⟩) {12    results(chan int)(⟨addr B⟩) <- job1 * 1013  }
    All 3 passes — pass 1 is the card above
    passjob
    11
    22
    34

  5. first ← 10, second ← 20, third ← 40

    22  first→ 10 := <-results(chan int)(⟨addr B⟩)23  second→ 20 := <-results(chan int)(⟨addr B⟩)24  third→ 40 := <-results(chan int)(⟨addr B⟩)25  fmt.Println("jobs=", len(inputs[]int{1, 2, 4}))26  fmt.Println("first=", first10)27  fmt.Println("second=", second20)28  fmt.Println("third=", third40)29}
    outputjobs= 3
first= 10
second= 20
third= 40

  1. extraJob ← 5, jobs ← (chan int)(⟨addr A⟩), results ← (chan int)(⟨addr B⟩)

    5func main() {6  var extraJob→ 5 = 57  jobs→ (chan int)(⟨addr A⟩) := make(chan int, 3)8  results→ (chan int)(⟨addr B⟩) := make(chan int, 3)910  go func() {11    for job := range jobs {12      results <- job * 1013    }14  }()1516  inputs→ []int{1, 2, 5} := []int{1, 2, extraJob5}17  for _, job := range inputs {

  2. for _, job := range inputs

    pass 1 of 3
    16inputs := []int{1, 2, extraJob}17for _, job1 := range inputs[]int{1, 2, 5} {18  jobs <- job
    All 3 passes — pass 1 is the card above
    passjobjobs
    11—
    22—
    35(chan int)(⟨addr A⟩)

  3. jobs <- job

    17for _, job := range inputs {18  jobs(chan int)(⟨addr A⟩) <- job119}

  4. for job := range jobs

    pass 1 of 3
    10go func() {11  for job1 := range jobs(chan int)(⟨addr A⟩) {12    results <- job * 10
    All 3 passes — pass 1 is the card above
    passjobresults
    11—
    22(chan int)(⟨addr B⟩)
    35(chan int)(⟨addr B⟩)

  5. jobs <- job

    11  for job := range jobs {12    results(chan int)(⟨addr B⟩) <- job1 * 1013  }14}()1516inputs := []int{1, 2, extraJob}17for _, job := range inputs {18  jobs(chan int)(⟨addr A⟩) <- job219}

  6. jobs <- job

    17for _, job := range inputs {18  jobs(chan int)(⟨addr A⟩) <- job219}

  7. first ← 10, second ← 20

    19}20close(jobs(chan int)(⟨addr A⟩))2122first→ 10 := <-results(chan int)(⟨addr B⟩)23second→ 20 := <-results(chan int)(⟨addr B⟩)24third := <-results(chan int)(⟨addr B⟩)25fmt.Println("jobs=", len(inputs))

  8. third ← 50

    23  second := <-results24  third→ 50 := <-results(chan int)(⟨addr B⟩)25  fmt.Println("jobs=", len(inputs[]int{1, 2, 5}))26  fmt.Println("first=", first10)27  fmt.Println("second=", second20)28  fmt.Println("third=", third50)29}
    outputjobs= 3
first= 10
second= 20
third= 50