add locker

concurrency/locker/main.go

@@ -0,0 +1,35 @@
+package main
+
+/**
+In a particularly sensitive portion of code, you need to lock certain resources. Given
+the frequent use of channels in your code, you’d like to do this with channels instead
+of the sync package.
+
+When talking about using a channel as a lock, you want this kind of behavior:
+1 A function acquires a lock by sending a message on a channel.
+2 The function proceeds to do its sensitive operations.
+3 The function releases the lock by reading the message back off the channel.
+4 Any function that tries to acquire the lock before it’s been released will pause
+when it tries to acquire the (already locked) lock.
+**/
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	lock := make(chan bool, 1)
+	for i := 1; i < 7; i++ {
+		go worker(i, lock)
+	}
+	time.Sleep(time.Second * 10)
+}
+
+func worker(id int, lock chan bool) {
+	fmt.Printf("%d wants the lock\n", id)
+	lock <- true
+	fmt.Printf("%d has the lock\n", id)
+	time.Sleep(500 * time.Millisecond)
+	fmt.Printf("%d is releasing the lock\n", id)
+	<-lock
+}