golang 框架通过限流和熔断提升并发能力，具体实现如下：限流：限制每秒请求数量，防止系统超负荷，实现方式为使用令牌桶算法；熔断：当系统故障时暂停处理请求，防止故障传播，实现方式为使用断路器模式，设置最大失败次数、打开时间和复位时间。

Golang 框架如何通过限流和熔断提高系统的并发能力

限流

限流是一种用来限制系统每秒钟处理请求数量的技术。它可以防止系统超负荷，从而导致性能下降或崩溃。在 Golang 中，可以使用以下代码段来实现限流：

import (
    "context"
    "errors"
    "time"
)

// Limit is a struct that implements the Token Bucket algorithm
type Limit struct {
    rate  time.Duration
    burst int
    queue chan struct{}
    ctx   context.Context
    cancel context.CancelFunc
}

// NewLimit creates a new Limit
func NewLimit(rate time.Duration, burst int) *Limit {
    ctx, cancel := context.WithCancel(context.Background())
    return &Limit{
        rate:  rate,
        burst: burst,
        queue: make(chan struct{}, burst),
        ctx:   ctx,
        cancel: cancel,
    }
}

// Wait waits for a token to become available and then consumes it
func (l *Limit) Wait() error {
    select {
    case <-l.ctx.Done():
        return errors.New("context canceled")
    case <-l.queue:
        return nil
    }
}

// Acquire acquires a token and increments the counter
func (l *Limit) Acquire() error {
    if err := l.Wait(); err != nil {
        return err
    }

    go func() {
        time.Sleep(l.rate)
        select {
        case l.queue <- struct{}{}:
        case <-l.ctx.Done():
        }
    }()

    return nil
}

熔断

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熔断是一种当系统出现故障时暂时停止处理请求的技术。它可以防止故障传播并允许系统自我恢复。在 Golang 中，可以使用以下代码段来实现熔断：

import (
    "context"
    "sync/atomic"
    "time"
)

// CircuitBreaker is a struct that implements the Circuit Breaker pattern
type CircuitBreaker struct {
    maxFailures    int
    openTime       time.Duration
    resetTime      time.Duration
    count          int64
    state          string
    openAt         time.Time
    resetAt        time.Time
    closedAt       time.Time
    lastFailedAt   time.Time
    totalFailures  int64
    totalSuccesses int64
}

// NewCircuitBreaker creates a new CircuitBreaker
func NewCircuitBreaker(maxFailures int, openTime time.Duration, resetTime time.Duration) *CircuitBreaker {
    return &CircuitBreaker{
        maxFailures: maxFailures,
        openTime:    openTime,
        resetTime:   resetTime,
        state:       "CLOSED",
        closedAt:    time.Now(),
    }
}

// Execute executes a function and handles circuit breaker logic
func (cb *CircuitBreaker) Execute(f func()) {
    switch cb.state {
    case "OPEN":
        if time.Since(cb.openAt) > cb.openTime {
            cb.setState("HALF_OPEN")
            cb.openAt = time.Now()
        }
        return
    case "HALF_OPEN":
        if time.Since(cb.resetAt) > cb.resetTime {
            cb.setState("CLOSED")
            cb.resetAt = time.Now()
        }
    }

    start := time.Now()
    f()
    end := time.Since(start)

    if end >= cb.openTime {
        atomic.AddInt64(&cb.count, 1)
    } else {
        atomic.AddInt64(&cb.totalSuccesses, 1)
    }

    if atomic.LoadInt64(&cb.count) >= int64(maxFailures) {
        cb.setState("OPEN")
        cb.count = 0
    }
}

// setState changes the state of the circuit breaker
func (cb *CircuitBreaker) setState(state string) {
    switch state {
    case "OPEN":
        cb.state = "OPEN"
        cb.openAt = time.Now()
    case "HALF_OPEN":
        cb.state = "HALF_OPEN"
        cb.resetAt = time.Now()
    case "CLOSED":
        cb.state = "CLOSED"
        cb.closedAt = time.Now()
    }
}

实战案例

以下是一个使用限流和熔断来提高 Golang 应用并发能力的实战案例：

import (
    "context"
    "fmt"
    "log"
    "net/http"
    "sync"
    "time"

    "github.com/google/go-github/v42/github"
)

// Limit the number of requests to the GitHub API
var rateLimiter = NewLimit(time.Second, 10)

// Circuit breaker to prevent overloading the GitHub API
var cb = NewCircuitBreaker(3, time.Minute, time.Minute*5)

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        if err := acquireToken(); err != nil {
            // Handle error
            return
        }

        cb.Execute(func() {
            // Make request to GitHub API
            client := github.NewClient(nil)
            ctx := context.Background()
            repos, _, err := client.Repositories.List(ctx, "", nil)
            if err != nil {
                // Handle error
                return
            }

            for _, repo := range repos {
                fmt.Fprintf(w, "%sn", repo.GetFullName())
            }
        })
    })

    log.Fatal(http.ListenAndServe(":8080", nil))
}

// acquireToken blocks until a token is available and then consumes it
func acquireToken() error {
    if err := rateLimiter.Acquire(); err != nil {
        return err
    }

    return nil
}

在这个示例中，rateLimiter 用于限制对 GitHub API 的请求速率，而 cb 则用于防止因故障导致请求过载。这使得应用程序能够以受控和健壮的方式处理来自用户的请求，从而提高了系统的整体并发能力。