如何实现限流器，请用chan实现一种限流器，也可以不用chan实现

题目来源： 字节跳动

答案：

使用计数器实现请求限流

限流的要求是在指定的时间间隔内，server 最多只能服务指定数量的请求。实现的原理是我们启动一个计数器，每次服务请求会把计数器加一，同时到达指定的时间间隔后会把计数器清零；这个计数器的实现代码如下所示：

package main
import (
    "fmt"
    "io"
    "net/http"
    "sync"
    "time"
)
type RequestLimitService struct {
    Interval time.Duration
    MaxCount int
    Lock     sync.Mutex
    ReqCount int
}
func NewRequestLimitService(interval time.Duration, maxCnt int) *RequestLimitService {
    reqLimit := &RequestLimitService{
        Interval: interval,
        MaxCount: maxCnt,
    }
    go func() {
        ticker := time.NewTicker(interval)
        for {
            <-ticker.C
            reqLimit.Lock.Lock()
            fmt.Println("Reset Count...")
            reqLimit.ReqCount = 0
            reqLimit.Lock.Unlock()
        }
    }()
    return reqLimit
}
func (reqLimit *RequestLimitService) Increase() {
    reqLimit.Lock.Lock()
    defer reqLimit.Lock.Unlock()
    reqLimit.ReqCount += 1
}
func (reqLimit *RequestLimitService) IsAvailable() bool {
    reqLimit.Lock.Lock()
    defer reqLimit.Lock.Unlock()
    return reqLimit.ReqCount < reqLimit.MaxCount
}
var RequestLimit = NewRequestLimitService(10 * time.Second, 5)
func helloHandler(w http.ResponseWriter, r *http.Request) {
    if RequestLimit.IsAvailable() {
        RequestLimit.Increase()
        fmt.Println(RequestLimit.ReqCount)
        io.WriteString(w, "Hello world!
")
    } else {
        fmt.Println("Reach request limiting!")
        io.WriteString(w, "Reach request limit!
")
    }
}
func main() {
    fmt.Println("Server Started!")
    http.HandleFunc("/", helloHandler)
    http.ListenAndServe(":8000", nil)
}