adding cases for mutexes examples

Author: symonk

mutexes/main.go

@@ -1,6 +1,60 @@
 package mutexes
 
+import (
+	"fmt"
+	"sync"
+)
+
 // Allows for more complex state synchronisation
 // Across multiple goroutines where atomic/counters
 // are not enough.
-func Run() {}
+func Run() {
+	container := &Container{counters: map[string]int{"A": 0, "B": 0}}
+	var wg sync.WaitGroup
+	doIncrement := func(name string, n int) {
+		for i := 0; i < n; i++ {
+			container.Increment(name)
+		}
+		wg.Done()
+	}
+	wg.Add(5)
+	go doIncrement("A", 10000)
+	go doIncrement("B", 15000)
+	go doIncrement("C", 5000)
+	go doIncrement("A", 15000)
+	go doIncrement("B", 25000)
+	wg.Wait()
+	fmt.Println(container.counters)
+	container.CheckCounterIs("A", 25000)
+	container.CheckCounterIs("B", 40000)
+	container.CheckCounterIs("C", 5000)
+
+}
+
+// A simple type that stores counter hits.
+// Default state(s) of mutexes are usable.
+// Note: Mutexes should not be copied; so pass this by pointer.
+type Container struct {
+	counters map[string]int
+	mutex sync.Mutex
+}
+
+// Acquire the mutex lock and carry out the work.
+func (c *Container) Increment(counter string) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	c.counters[counter]++
+}
+
+// Assert a counter (safely) has a particular value at a point in time.
+func (c *Container) CheckCounterIs(counter string, expected int) {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	lookup, ok := c.counters[counter]
+	if !ok {
+		panic(fmt.Sprintf("Counter did not contain %s key.", counter))
+	}
+	if lookup != expected {
+		panic(fmt.Sprintf("Counter key %s was not equal to %d", counter, expected))
+	}
+}