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Commit 966eea8

Browse files
add more mutexes exercises
1 parent 83e7577 commit 966eea8

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28 files changed

+1093
-32
lines changed

28 files changed

+1093
-32
lines changed

‎mutexes/README.md‎

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@@ -134,5 +134,6 @@ the database consistency which otherwise is not possible for a non-serial schedu
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- [raceacquire - Go Source Code](https://github.com/golang/go/blob/master/src/runtime/race.go#L515)
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- [racecall - Go Source Code](https://github.com/golang/go/blob/master/src/runtime/race.go#L348)
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- [racecall - GOASM Source Code](https://github.com/golang/go/blob/master/src/runtime/race_amd64.s#L384)
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- [RWMutex - Go Source Code](https://github.com/golang/go/blob/master/src/sync/rwmutex.go#L28)
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[Home](https://github.com/golang-basics/concurrency)

‎mutexes/atomic-mutex-mix/main.go‎

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package main
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import (
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"fmt"
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"sync"
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"sync/atomic"
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)
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// try running this with the -race flag
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// go run -race main.go
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func main() {
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var count int32
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var mu sync.Mutex
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var wg sync.WaitGroup
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for i := 0; i < 10000; i++ {
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wg.Add(2)
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go func() {
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defer wg.Done()
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atomic.AddInt32(&count, 1)
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}()
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go func() {
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defer wg.Done()
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mu.Lock()
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count++
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mu.Unlock()
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}()
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}
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wg.Wait()
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// the result is correct, but Go is not able to properly detect a race condition
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// due to mixed usage of Mutex and Atomics
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fmt.Println("count:", count)
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}

‎mutexes/deadlock-and-race/main.go‎

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package main
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import (
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"fmt"
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"sync"
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)
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// Having both deadlock and race
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// will result in the program hanging
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// when ran with -race flag
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// go run -race main.go => will show races, but hang forever
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// Try running the program first without -race => fix the deadlock
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// go run main.go
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// then using the -race flag => fix the race condition
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// go run -race main.go
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func main() {
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var count int
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var mu sync.Mutex
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var wg sync.WaitGroup
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wg.Add(2)
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go func() {
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defer wg.Done()
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count++
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}()
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go func() {
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defer wg.Done()
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count++
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}()
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wg.Wait()
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mu.Lock()
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mu.Lock()
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fmt.Println("count:", count)
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}

‎mutexes/exercises/1/exercise.go‎

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package main
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import (
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"fmt"
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"sync"
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"sync/atomic"
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)
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// EXERCISE:
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// Find what's wrong in the following code
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// Make sure all the tests are passing
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// Make sure there's no deadlock or race condition
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// Hint: Limit the go routines (100), then find and fix the deadlock first
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// try running this with the -race flag
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// go run -race exercise.go
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// run the tests using:
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// GOFLAGS="-count=1" go test -race .
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func main() {
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clicks := exercise()
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fmt.Println("total clicks:", clicks.total)
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}
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func exercise() clickCounter {
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var mu sync.Mutex
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var wg sync.WaitGroup
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clicks := clickCounter{
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mu: &mu,
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elements: map[string]int{
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"btn1": 0,
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"btn2": 0,
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},
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}
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for i := 0; i < 1000; i++ {
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wg.Add(3)
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go func() {
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defer wg.Done()
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if len(clicks.elements) > 10 {
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fmt.Println("we got more than 10 elements")
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}
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}()
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go func() {
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defer wg.Done()
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clicks.add("btn1")
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clicks.add("btn2")
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}()
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go func() {
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defer wg.Done()
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total := atomic.LoadInt64(&clicks.total)
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if total > 20 {
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fmt.Println("something is wrong")
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}
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}()
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}
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wg.Wait()
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return clicks
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}
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type clickCounter struct {
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mu *sync.Mutex
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elements map[string]int
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total int64
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}
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func (c *clickCounter) add(element string) {
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c.mu.Lock()
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if c.elements[element]+1 > 10 {
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return
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}
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c.elements[element]++
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c.total++
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c.mu.Unlock()
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}

‎mutexes/exercises/1/exercise_test.go‎

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package main
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import (
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"testing"
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)
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// GOFLAGS="-count=1" go test -race .
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func TestExercise(t *testing.T) {
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clicks := exercise()
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n1 := clicks.elements["btn1"]
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n2 := clicks.elements["btn2"]
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total := clicks.total
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if n1 != 10 {
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t.Fatalf("expected number of clicks for btn1: %d, got: %d", 10, n1)
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}
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if n2 != 10 {
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t.Fatalf("expected number of clicks for btn2: %d, got: %d", 10, n2)
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}
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if total != 20 {
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t.Fatalf("expected total to be: %d, got: %d", 20, total)
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}
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}
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package main
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import (
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"fmt"
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"sync"
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)
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// EXERCISE:
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// Find what's wrong in the following code
10+
// Make sure all the tests are passing
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// Make sure there's no deadlock or race condition
12+
// Hint: Limit the go routines (100), then find and fix the deadlock first
13+
14+
// try running this with the -race flag
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// go run -race exercise.go
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// run the tests using:
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// GOFLAGS="-count=1" go test -race .
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func main() {
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clicks := exercise()
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fmt.Println("total clicks:", clicks.total)
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}
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func exercise() clickCounter {
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var mu sync.Mutex
26+
var wg sync.WaitGroup
27+
clicks := clickCounter{
28+
mu: &mu,
29+
elements: map[string]int{
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"btn1": 0,
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"btn2": 0,
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},
33+
}
34+
35+
for i := 0; i < 1000; i++ {
36+
wg.Add(3)
37+
go func() {
38+
defer wg.Done()
39+
clicks.mu.Lock()
40+
defer clicks.mu.Unlock()
41+
if len(clicks.elements) > 10 {
42+
fmt.Println("we got more than 10 elements")
43+
}
44+
}()
45+
go func() {
46+
defer wg.Done()
47+
clicks.add("btn1")
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clicks.add("btn2")
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}()
50+
go func() {
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defer wg.Done()
52+
clicks.mu.Lock()
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defer clicks.mu.Unlock()
54+
if clicks.total > 20 {
55+
fmt.Println("something is wrong")
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}
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}()
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}
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wg.Wait()
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return clicks
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}
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type clickCounter struct {
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mu *sync.Mutex
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elements map[string]int
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total int64
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}
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func (c *clickCounter) add(element string) {
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c.mu.Lock()
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defer c.mu.Unlock()
73+
if c.elements[element]+1 > 10 {
74+
return
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}
76+
c.elements[element]++
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c.total++
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}

‎mutexes/exercises/2/exercise.go‎

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package main
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import (
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"fmt"
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"strconv"
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"sync"
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"time"
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)
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10+
// EXERCISE:
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// Find what's wrong in the following code
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// Make sure all the tests are passing
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// DO NOT remove any Sleep() calls
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// try running this with the -race flag
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// go run -race exercise.go
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// run the tests using:
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// GOFLAGS="-count=1" go test .
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func main() {
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c := &catalog{data: map[string]string{
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"p1": "apples",
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"p2": "oranges",
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"p3": "grapes",
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"p4": "pineapple",
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"p5": "bananas",
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}}
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now := time.Now()
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exercise(c, "p1", "p2", "p3", "p4", "p5")
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fmt.Println("elapsed:", time.Since(now))
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}
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func exercise(c *catalog, ids ...string) {
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var wg sync.WaitGroup
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wg.Add(1000)
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for i := 0; i < 1000; i++ {
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go func(i int) {
40+
defer wg.Done()
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for _, id := range ids {
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c.get(id)
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}
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c.add("generated_"+strconv.Itoa(i), "generated product")
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}(i+1)
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}
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wg.Wait()
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}
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type catalog struct {
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mu sync.Mutex
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data map[string]string
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}
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func (c *catalog) add(id, product string) {
57+
c.mu.Lock()
58+
defer c.mu.Unlock()
59+
// simulate load
60+
time.Sleep(500*time.Nanosecond)
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c.data[id] = product
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}
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func (c *catalog) get(id string) string {
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c.mu.Lock()
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defer c.mu.Unlock()
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// simulate load
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time.Sleep(500*time.Nanosecond)
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// avoid key existence check
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return c.data[id]
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}

‎mutexes/exercises/2/exercise_test.go‎

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package main
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import (
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"testing"
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"time"
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)
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8+
// GOFLAGS="-count=1" go test .
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func TestExercise(t *testing.T) {
10+
c := &catalog{data: map[string]string{
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"p1": "apples",
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"p2": "oranges",
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"p3": "grapes",
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"p4": "pineapple",
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"p5": "bananas",
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}}
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18+
now := time.Now()
19+
exercise(c, "p1", "p2", "p3", "p4", "p5")
20+
elapsed := time.Since(now)
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numberOfProducts := len(c.data)
22+
23+
if numberOfProducts != 1005 {
24+
t.Fatalf("wrong number of products in the catalog, got: %d", numberOfProducts)
25+
}
26+
if elapsed > 10*time.Millisecond {
27+
t.Fatalf("exercise took too long, elapsed: %v", elapsed)
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}
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}

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