good good study, day day up!

vendor/gopl.io/ch9/bank3/bank.go

@@ -0,0 +1,30 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 263.
+
+// Package bank provides a concurrency-safe single-account bank.
+package bank
+
+//!+
+import "sync"
+
+var (
+	mu      sync.Mutex // guards balance
+	balance int
+)
+
+func Deposit(amount int) {
+	mu.Lock()
+	balance = balance + amount
+	mu.Unlock()
+}
+
+func Balance() int {
+	mu.Lock()
+	b := balance
+	mu.Unlock()
+	return b
+}
+
+//!-