今天面試golang碰到了一道考并發和鎖的題目,沒有完成,是以把它記錄下來,僅為以後複習。
場景:在一個高并發的web伺服器中,要限制IP的頻繁通路。現模拟100個IP同時并發通路伺服器,每個IP要重複通路1000次。每個IP三分鐘之内隻能通路一次。修改以下代碼完成該過程,要求能成功輸出 success:100
package main
import (
"fmt"
"time"
)
type Ban struct {
visitIPs map[string]time.Time
}
func NewBan() *Ban {
return &Ban{visitIPs: make(map[string]time.Time)}
}
func (o *Ban) visit(ip string) bool {
if _, ok := o.visitIPs[ip]; ok {
return true
}
o.visitIPs[ip] = time.Now()
return false
}
func main() {
success := 0
ban := NewBan()
for i := 0; i < 1000; i++ {
for j := 0; j < 100; j++ {
go func() {
ip := fmt.Sprintf("192.168.1.%d", j)
if !ban.visit(ip) {
success++
}
}()
}
}
fmt.Println("success:", success)
}
以上代碼有一些坑。當時也是沒有做出來,回來請教一位大佬,得以解決。
package main
import (
"fmt"
"sync"
"sync/atomic"
"time"
)
type Ban struct {
visitIPs map[string]struct{}
}
func NewBan() *Ban {
return &Ban{visitIPs: make(map[string]struct{})}
}
//判斷IP是否存在
func (o *Ban) visit(ip string) bool {
mapMutex.Lock()
defer mapMutex.Unlock()
if _, ok := o.visitIPs[ip]; ok {
return true
}
o.visitIPs[ip] = struct{}{}
go o.invalidAfter3Min(ip)
return false
}
// 3分鐘後ip失效, 從map中移除. 是以ip再次通路時便可正常通路
func (o *Ban) invalidAfter3Min(ip string) {
time.Sleep(time.Minute * 3)
mapMutex.Lock()
visitIPs := o.visitIPs
delete(visitIPs, ip)
o.visitIPs = visitIPs
mapMutex.Unlock()
}
var mapMutex *sync.Mutex // mutex to avoid concurrent map writes
func main() {
mapMutex = new(sync.Mutex)
var success int64
ban := NewBan()
wg := new(sync.WaitGroup)
for i := 0; i < 1000; i++ {
for j := 0; j < 100; j++ {
wg.Add(1)
ipEnd := j
go func() {
defer wg.Done()
ip := fmt.Sprintf("192.168.1.%d", ipEnd)
if !ban.visit(ip) {
atomic.AddInt64(&success, 1)
}
}()
}
}
wg.Wait()
fmt.Println("success:", success)
}
主要用到了閉包,原子操作和鎖實作
---------------------
作者:自傷無色丶
來源:CSDN
原文:https://blog.csdn.net/qq_28163175/article/details/75287877
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轉載于:https://www.cnblogs.com/smallleiit/p/10891011.html