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Changes: - Renamed all 10 Golang files from English to Chinese names - Created 00-项目概述/项目概述.md with comprehensive project overview - Created 08-算法与数据结构/算法与数据结构学习指南.md with detailed learning guide - Created 12-面试技巧/面试准备进度.md with progress tracking - Added .obsidian configuration for better markdown editing - Updated Claude.MD with Chinese filename rule Generated with [Claude Code](https://claude.ai/code) via [Happy](https://happy.engineering) Co-Authored-By: Claude <noreply@anthropic.com> Co-Authored-By: Happy <yesreply@happy.engineering>
391 lines
7.2 KiB
Markdown
391 lines
7.2 KiB
Markdown
# Goroutine 和并发模型
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## 问题
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1. 什么是 Goroutine？与线程的区别？
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2. 如何优雅地关闭 Goroutine？
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3. Channel 的底层实现原理是什么？
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4. select 的作用是什么？
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5. context 包的作用是什么？
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6. 如何避免 Goroutine 泄漏？
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7. Go 的调度器（GMP 模型）是怎样的？
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---
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## 标准答案
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### 1. Goroutine vs 线程
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#### **对比**
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| 特性 | Goroutine | 线程 |
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| -------- | ----------- | ------ |
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| **内存占用** | 2 KB（初始） | 1-2 MB |
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| **创建成本** | 极低 | 较高 |
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| **切换成本** | 低（用户态） | 高（内核态） |
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| **数量** | 数十万+ | 数千个 |
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| **调度** | Go 调度器（GMP） | 操作系统 |
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| **栈** | 动态伸缩（按需增长） | 固定大小 |
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---
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#### **创建 Goroutine**
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```go
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func hello(name string) {
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fmt.Println("Hello,", name)
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}
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func main() {
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// 启动 Goroutine
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go hello("Alice")
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go hello("Bob")
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// 等待（防止主 Goroutine 退出）
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time.Sleep(time.Second)
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}
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```
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---
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### 2. 优雅关闭 Goroutine
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#### **问题示例**
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```go
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// ❌ 无法停止
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func worker() {
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for {
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fmt.Println("working...")
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time.Sleep(time.Second)
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}
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}
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func main() {
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go worker()
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time.Sleep(3 * time.Second)
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// 程序退出，worker 未清理
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}
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```
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---
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#### **解决方案：使用 channel**
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```go
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func worker(stop <-chan struct{}) {
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for {
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select {
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case <-stop:
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fmt.Println("worker stopping...")
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return
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default:
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fmt.Println("working...")
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time.Sleep(time.Second)
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}
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}
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}
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func main() {
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stop := make(chan struct{})
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go worker(stop)
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time.Sleep(3 * time.Second)
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close(stop) // 发送停止信号
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time.Sleep(time.Second)
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}
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```
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---
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### 3. Channel 底层实现
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#### **Channel 结构**
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```go
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type hchan struct {
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qcount uint // 队列中的数据量
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dataqsiz uint // 环形队列大小
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buf unsafe.Pointer // 环形队列指针
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elemsize uint16 // 元素大小
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closed uint32 // 是否关闭
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elemtype *_type // 元素类型
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sendx uint64 // 发送索引
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recvx uint64 // 接收索引
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recvq waitq // 接收等待队列
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sendq waitq // 发送等待队列
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lock mutex // 互斥锁
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}
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```
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---
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#### **Channel 类型**
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**1. 无缓冲 Channel**：
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```go
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ch := make(chan int)
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// 发送会阻塞，直到有接收者
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go func() {
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ch <- 1 // 阻塞
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}()
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<-ch // 接收
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```
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**2. 有缓冲 Channel**：
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```go
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ch := make(chan int, 10) // 缓冲大小 10
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// 缓冲未满时，发送不阻塞
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ch <- 1
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ch <- 2
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```
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---
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### 4. select 的作用
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#### **多路复用**
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```go
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func worker1(ch chan<- int) {
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time.Sleep(1 * time.Second)
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ch <- 1
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}
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func worker2(ch chan<- int) {
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time.Sleep(2 * time.Second)
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ch <- 2
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}
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func main() {
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ch1 := make(chan int)
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ch2 := make(chan int)
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go worker1(ch1)
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go worker2(ch2)
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select {
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case val := <-ch1:
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fmt.Println("worker1:", val)
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case val := <-ch2:
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fmt.Println("worker2:", val)
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case <-time.After(3 * time.Second):
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fmt.Println("timeout")
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}
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}
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```
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---
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#### **select 的特性**
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1. **随机选择**：多个 case 就绪时随机选择
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2. **阻塞**：所有 case 不就绪时阻塞
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3. **default**：添加 default 后，select 不阻塞
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```go
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ch := make(chan int)
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select {
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case val := <-ch:
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fmt.Println(val)
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default:
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fmt.Println("no data")
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}
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```
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---
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### 5. context 包
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#### **作用**
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1. **超时控制**
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2. **取消信号传递**
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3. **元数据传递**
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---
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#### **使用示例**
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**1. 超时控制**：
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```go
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func doWork(ctx context.Context) {
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for {
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select {
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case <-ctx.Done():
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fmt.Println("work cancelled:", ctx.Err())
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return
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default:
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fmt.Println("working...")
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time.Sleep(500 * time.Millisecond)
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}
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}
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}
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func main() {
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ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
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defer cancel()
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go doWork(ctx)
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time.Sleep(3 * time.Second)
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}
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```
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---
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**2. 取消信号**：
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```go
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func main() {
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ctx, cancel := context.WithCancel(context.Background())
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go func() {
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time.Sleep(1 * time.Second)
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cancel() // 取消
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}()
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select {
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case <-ctx.Done():
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fmt.Println("cancelled:", ctx.Err())
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}
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}
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```
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---
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**3. 元数据传递**：
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```go
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func handler(ctx context.Context) {
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userID := ctx.Value("userID").(string)
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fmt.Println("userID:", userID)
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}
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func main() {
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ctx := context.WithValue(context.Background(), "userID", "12345")
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handler(ctx)
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}
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```
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---
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### 6. 避免 Goroutine 泄漏
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#### **问题示例**
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```go
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// ❌ Goroutine 泄漏
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func query() {
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ch := make(chan int)
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go func() {
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val := <-ch // 永久阻塞
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fmt.Println(val)
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}()
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// 如果没有数据发送到 ch，Goroutine 永久泄漏
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}
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```
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---
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#### **解决方案**
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**1. 使用 context**：
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```go
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func query(ctx context.Context) {
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ch := make(chan int)
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go func() {
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select {
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case val := <-ch:
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fmt.Println(val)
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case <-ctx.Done():
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return // 超时或取消时退出
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}
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}()
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select {
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case ch <- 1:
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case <-time.After(1 * time.Second):
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fmt.Println("timeout")
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}
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}
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```
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---
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**2. 使用缓冲 Channel**：
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```go
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func query() {
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ch := make(chan int, 1) // 缓冲大小 1
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go func() {
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val := <-ch
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fmt.Println(val)
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}()
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ch <- 1 // 不会阻塞
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}
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```
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---
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### 7. GMP 调度模型
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#### **组成**
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- **G（Goroutine）**：用户级线程（轻量级）
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- **M（Machine）**：系统线程（与内核线程 1:1）
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- **P（Processor）**：逻辑处理器（M 的队列，运行 Go 代码）
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---
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#### **GMP 模型**
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```
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P1 (Processor) P2 (Processor) P3 (Processor)
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│ │ │
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├─ G1 ├─ G5 ├─ G9
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├─ G2 ├─ G6 ├─ G10
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└─ G3 └─ G7 └─ G11
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│ │ │
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↓ ↓ ↓
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M1 (Thread) M2 (Thread) M3 (Thread)
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```
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**工作流程**：
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1. P 维护一个 Goroutine 队列
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2. P 从队列中取出 G，执行
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3. G 阻塞（I/O、channel）时，P 继续执行其他 G
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4. P 空闲时，从其他 P "偷" G（工作窃取）
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---
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#### **调度策略**
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1. **Work-Stealing（工作窃取）**：P 从其他 P 窃取 G
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2. **抢占式调度**：sysmon 线程抢占长时间运行的 G
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3. **Time Slice（时间片）**：每个 G 执行 10ms 后调度
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---
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### 8. 阿里 P7 加分项
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**深度理解**：
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- 理解 Go 调度器的实现原理（GMP 模型）
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- 理解 Channel 的底层实现（环形队列、锁）
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- 理解 context 的传播机制
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**实战经验**：
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- 有处理 Goroutine 泄漏的经验
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- 有处理并发竞争条件的经验
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- 有性能优化的经验（减少锁、使用 sync.Pool）
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**性能优化**：
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- 理解如何避免 Goroutine 泄漏
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- 理解如何减少 Channel 阻塞
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- 理解如何提高并发性能（Worker Pool、批处理）
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