Go语言中bytes.Buffer的并发安全性探究与实现

package main

import (
    "bytes"
    "fmt"
    "runtime"
    "sync"
)

func main() {
    var b bytes.Buffer
    var wg sync.WaitGroup
    numWriters := 100
    dataToWrite := []byte("hello")

    // 限制CPU核心数，更容易观察到竞态条件
    runtime.GOMAXPROCS(1)

    for i := 0; i < numWriters; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            // 并发写入，没有锁保护
            b.Write(dataToWrite)
        }()
    }

    wg.Wait()

    // 打印最终缓冲区内容和长度
    // 期望长度是 numWriters * len(dataToWrite)
    // 实际内容可能混乱，长度也可能不正确
    fmt.Printf("Expected length: %d\n", numWriters*len(dataToWrite))
    fmt.Printf("Actual length: %d\n", b.Len())
    // fmt.Printf("Actual content: %s\n", b.String()) // 内容可能非常混乱，不建议打印
    if b.Len() != numWriters*len(dataToWrite) {
        fmt.Println("Error: Buffer length is incorrect due to race condition!")
    } else {
        fmt.Println("Buffer length is correct (might be lucky, still not thread-safe).")
    }
}

package main

import (
    "bytes"
    "fmt"
    "runtime"
    "sync"
)

// SafeBuffer 是一个并发安全的 bytes.Buffer 封装
type SafeBuffer struct {
    buf bytes.Buffer
    mu  sync.Mutex
}

// Write 将 p 的内容写入 SafeBuffer
func (sb *SafeBuffer) Write(p []byte) (n int, err error) {
    sb.mu.Lock()         // 加锁
    defer sb.mu.Unlock() // 确保解锁
    return sb.buf.Write(p)
}

// String 返回 SafeBuffer 的内容作为字符串
func (sb *SafeBuffer) String() string {
    sb.mu.Lock()
    defer sb.mu.Unlock()
    return sb.buf.String()
}

// Len 返回 SafeBuffer 中字节的数量
func (sb *SafeBuffer) Len() int {
    sb.mu.Lock()
    defer sb.mu.Unlock()
    return sb.buf.Len()
}

func main() {
    var sb SafeBuffer // 使用我们自定义的 SafeBuffer
    var wg sync.WaitGroup
    numWriters := 100
    dataToWrite := []byte("hello")

    runtime.GOMAXPROCS(1) // 同样限制CPU核心数，但现在应该不会有问题了

    for i := 0; i < numWriters; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            sb.Write(dataToWrite) // 调用并发安全的写入方法
        }()
    }

    wg.Wait()

    expectedLen := numWriters * len(dataToWrite)
    actualLen := sb.Len()

    fmt.Printf("Expected length: %d\n", expectedLen)
    fmt.Printf("Actual length: %d\n", actualLen)

    if actualLen != expectedLen {
        fmt.Println("Error: Buffer length is incorrect even with mutex!")
    } else {
        fmt.Println("Success: Buffer length is correct and thread-safe.")
    }
    // fmt.Printf("Actual content (first 50 chars): %s...\n", sb.String()[:50]) // 可以安全打印部分内容
}