you're doing great

Author: GoesToEleven

000_temp/46_sp17/51_question/01/main.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var wg sync.WaitGroup
+
+type SafeCounter struct {
+	c int
+	sync.Mutex
+}
+
+func (c *SafeCounter) Add() {
+	c.Lock()
+	defer c.Unlock()
+	c.c++
+}
+
+var counter *SafeCounter = &SafeCounter{}
+
+func main() {
+
+	fmt.Println(&counter.c)
+
+	wg.Add(2)
+	go incrementor("Foo:")
+	go incrementor("Bar:")
+	wg.Wait()
+	fmt.Println("Final Counter:", counter.c)
+}
+
+func incrementor(s string) {
+	rand.Seed(time.Now().UnixNano())
+	for i := 0; i < 20; i++ {
+		x := counter
+		fmt.Println("1----",counter)
+		fmt.Println("2----",x)
+		x.Add()
+		counter = x
+		time.Sleep(time.Duration(rand.Intn(3)) * time.Millisecond)
+		fmt.Println(s, i, "Counter:", counter.c)
+	}
+	wg.Done()
+}
+
+// go run -race main.go
+// vs
+// go run main.go

000_temp/46_sp17/51_question/02/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var wg sync.WaitGroup
+
+type SafeCounter struct {
+	c int
+	m sync.Mutex
+}
+
+func (sc *SafeCounter) Add() {
+	sc.m.Lock()
+	defer sc.m.Unlock()
+	sc.c++
+}
+
+var counter *SafeCounter = &SafeCounter{}
+
+func main() {
+
+	fmt.Println(&counter.c)
+
+	wg.Add(2)
+	go incrementor("Foo:")
+	go incrementor("Bar:")
+	wg.Wait()
+	fmt.Println("Final Counter:", counter.c)
+}
+
+func incrementor(s string) {
+	rand.Seed(time.Now().UnixNano())
+	for i := 0; i < 20; i++ {
+		counter.Add()
+		time.Sleep(time.Duration(rand.Intn(3)) * time.Millisecond)
+		//fmt.Println(s, i, "Counter:", counter.c) // causes a race; no lock here; multiple goroutines accessing to READ the value
+	}
+	wg.Done()
+}
+
+// go run -race main.go
+// vs
+// go run main.go