Go language - what is critical resource security?

Critical resource security issues

Critical resources ： In concurrent programming , Can be used by multiple processes / Threads / Resources jointly accessed by the collaboration process .

If the critical resources are not handled properly in concurrent programming , It often leads to inconsistent data .

Ticket sales at the railway station demo, To demonstrate critical resource security issues

Realization 3 Tickets are sold at the same time

// Ticket allowance 
var tickets = 5

// Define synchronization waiting groups 
var wg sync.WaitGroup

func main() {
	wg.Add(3)
	go saleTickets("1 Ticket booth No ")
	go saleTickets("2 Ticket booth No ")
	go saleTickets("3 Ticket booth No ")
	wg.Wait()
}

func saleTickets(name string) {
	for {
		if tickets > 0 {
			fmt.Printf(" Ticket remaining :%v, %v Sell out \n", tickets, name)
			tickets--
		} else {
			fmt.Println(" The tickets have been sold out ...")
			wg.Done()
			break
		}
	}
}

Our parameters are totally set 5 Tickets , But the program finally sold 7 Tickets . This is the security of critical resources .

3 individual goroutine Judge whether the number of tickets is greater than at a certain time 0 When , At this moment, the number of tickets is enough . But when performing the next ticket selling operation , One of them goroutine The ticket office of sold the tickets first , But the other two ticket outlets have passed the logical judgment , Also sold tickets .

How to solve the safety problem of critical resources ？

1. Most languages solve the problem of synchronous resource security through locked The way . Only one is allowed at a time goroutine To access this shared data .go In language , Can use sync Lock operation under package .

2. stay go There is a classic saying in the concurrent programming of language ： Don't communicate by sharing memory , Instead, share memory by means of communication .Go Language encourages use channel Share state or change of share state in each goroutine Passed between , In this way, just like a lock, there is only one at a time goroutine Access shared state .