問題1 :
golang在講到共享變數時都會建議採用channel處理,
"Do not communicate by sharing memory; instead, share memory by communicating.”

於是我這邊試著改寫以下銀行範例,使用channel來做資料的處理
https://clouding.city/go/mutex-rwmutex/
但是使用go run -race main.go時仍會出現data race，
(（XX已解決）請問我的改法是哪裡出問題了呢？)
更正：原因似乎出在b.ReadBalance()，於是做了更正2的修正．延伸出問題2

package main

import (
	"fmt"
	"sync"
)

func main() {
	var wg sync.WaitGroup
	b := &Bank{}
	n := 10000
	wg.Add(n)
	valueCh := make(chan int)
	go b.ListenChanHandler(valueCh)
	for i := 1; i <= n; i++ {
		go func() {
			b.Deposit(100, valueCh) //同時存款
			wg.Done()
		}()

	}
	wg.Wait()
	fmt.Println(b.ReadBalance()) //印出 這個拿掉就不會data race
	fmt.Println("done")
}

type Bank struct {
	balance int
}

func (b *Bank) Deposit(amount int, valueCh chan int) {

	valueCh <- amount
}

func (b *Bank) ListenChanHandler(valueCh chan int) {
	go func() {
		for {
			select {
			case e := <-valueCh:
				b.balance = b.balance + e
			}
		}
	}()
}

func (b *Bank) ReadBalance() (balnce int) {
	balance := b.balance
	// fmt.Println("balance:", balance)
	return balance
}

更正2:
後來又用了鎖＋上channel一起用，data race就消失了

https://clouding.city/go/mutex-rwmutex/
package main

import (
	"fmt"
	"sync"
)

func main() {
	var wg sync.WaitGroup
	b := &Bank{}
	n := 10000
	wg.Add(n)
	valueCh := make(chan int)
	go b.ListenChanHandler(valueCh)
	for i := 1; i <= n; i++ {
		go func() {
			b.Deposit(100, valueCh) //同時存款
			wg.Done()
		}()

	}
	wg.Wait()
	fmt.Println(b.ReadBalance()) 
	fmt.Println("done")
}

type Bank struct {
	balance int
+	mux     sync.Mutex
}

func (b *Bank) Deposit(amount int, valueCh chan int) {

	valueCh <- amount
}

func (b *Bank) ListenChanHandler(valueCh chan int) {
	go func() {
		for {
			select {
			case e := <-valueCh:
+                               b.mux.Lock()
				b.balance = b.balance + e
+                               b.mux.Unlock()
			}
		}
	}()
}

func (b *Bank) ReadBalance() (balnce int) {
+	b.mux.Lock()
	balance := b.balance
+	b.mux.Unlock()
	// fmt.Println("balance:", balance)
	return balance
}

問題2: 竟然如此為什麼要用channel，這樣情況下單用原本的範例鎖會不會比較快？
好像不需要用上channel比較簡潔，
還是普遍有同時讀同時寫就使用鎖＋channel會更適用？
想知道有沒有這方面的場景比較分享呢？