A brief analysis of the current limiting algorithm in Golang

Golang, as a programming language with superior performance, is often used to handle high-concurrency server-side programs. When dealing with high concurrency, it is often necessary to limit the flow of requests to ensure the availability and stability of the service.

There are many popular current limiting algorithms in Golang, such as token bucket algorithm, leaky bucket algorithm, etc. Below we will use the token bucket algorithm as an example to introduce the implementation of these algorithms.

1. Principle of Token Bucket Algorithm

The token bucket algorithm is a relatively simple and effective current limiting algorithm. The principle is relatively simple, we can understand it with a bucket.

We can think of the request as water, and the token is the water in the bucket. Each request needs to obtain a token from the bucket before entering the system. When the bucket does not have a token, the request is rejected.

The bucket leaks water at a certain rate, that is, the system processes the number of requests at a certain rate. When the tokens in the bucket have not been taken out, the excess tokens will be stored in the bucket, waiting for the next request.

2. Golang implements the token bucket algorithm

Below we will use Golang to implement a simple token bucket algorithm.

1. Define a TokenBucket structure

First, we need to define a TokenBucket structure to save the parameters in the token bucket.

type TokenBucket struct {
    capacity   int           // 令牌桶容量
    rate       time.Duration // 令牌桶填充速率
    tokens     int           // 当前令牌数
    lastUpdate time.Time     // 上一次更新时间
}

2. Write the initialization function of TokenBucket

Next, we need to write a TokenBucket initialization function to initialize the parameters of the token bucket.

func NewTokenBucket(capacity int, rate time.Duration) *TokenBucket {
    return &TokenBucket{
        capacity:   capacity,
        rate:       rate,
        tokens:     0,
        lastUpdate: time.Now(),
    }
}

3. Implement the Take() method for TokenBucket

Next, we need to implement the Take() method for TokenBucket. This method is used to remove a token from the token bucket, and returns false if the token cannot be obtained.

func (tb *TokenBucket) Take() bool {
    tokens := tb.tokens - 1
    if tokens < 0 {
        return false
    }
    tb.tokens = tokens
    return true
}

4. Implement the Refill() method for TokenBucket

Next, we need to implement the Refill() method for TokenBucket to fill tokens regularly.

func (tb *TokenBucket) Refill() {
    now := time.Now()
    diff := now.Sub(tb.lastUpdate)
    tokens := int(diff / tb.rate)
    if tokens > 0 {
        tb.tokens = tb.tokens + tokens
        if tb.tokens > tb.capacity {
            tb.tokens = tb.capacity
        }
        tb.lastUpdate = now
    }
}

5. Implement the Run() method for TokenBucket

Finally, we need to implement the Run() method for TokenBucket and start a goroutine to fill and update the token.

func (tb *TokenBucket) Run() {
    ticker := time.NewTicker(tb.rate)
    go func() {
        for {
            select {
            case <-ticker.C:
                tb.Refill()
            }
        }
    }()
}

6. Use TokenBucket for current limiting

Using TokenBucket for current limiting is very simple. You only need to call the Take() method on each request. If true is returned, it means that the request can be made, otherwise the flow needs to be limited.

bucket := NewTokenBucket(100, time.Millisecond*10)
bucket.Run()

// 需要进行限流的请求
if !bucket.Take() {
    // 进行限流处理，以避免系统负载过高
}

3. Summary

Through the above code, we can see the simple implementation method of the token bucket algorithm. In actual projects, we can adjust and optimize according to specific needs, such as increasing the number of current limiting attempts, adjusting the filling rate, etc. Mastering the implementation methods of these current limiting algorithms is very helpful for understanding the design and implementation process of high-concurrency systems.

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