120 lines
2.7 KiB
Go
120 lines
2.7 KiB
Go
package main
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import (
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"fmt"
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"sync"
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)
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func main() {
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fmt.Println("=== 1. Slice 扩容机制 ===")
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demoSliceGrowth()
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fmt.Println("\n=== 2. Slice 深拷贝 vs 浅拷贝 ===")
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demoSliceCopy()
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fmt.Println("\n=== 3. Map 基本使用 ===")
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demoMapUsage()
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fmt.Println("\n=== 4. Map 并发写风险（会 panic！）===")
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// ⚠️ 下面这行默认注释掉，避免程序崩溃
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// demoUnsafeConcurrentMap()
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fmt.Println("\n=== 5. 安全的并发 map（sync.Map）===")
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demoSafeConcurrentMap()
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}
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// 1. 演示 slice 扩容机制
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func demoSliceGrowth() {
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var s []int
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fmt.Printf("初始: len=%d, cap=%d, addr=%p\n", len(s), cap(s), s)
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for i := 0; i < 10; i++ {
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s = append(s, i)
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fmt.Printf("append %d: len=%d, cap=%d, addr=%p\n", i, len(s), cap(s), s)
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}
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// 观察：当容量不足时，底层数组会重新分配，地址改变
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}
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// 2. 深拷贝 vs 浅拷贝
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func demoSliceCopy() {
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original := []int{1, 2, 3, 4, 5}
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shallow := original // 浅拷贝：共享底层数组
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deep := make([]int, len(original))
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copy(deep, original) // 深拷贝：独立底层数组
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fmt.Println("修改前:")
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fmt.Println("original:", original)
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fmt.Println("shallow :", shallow)
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fmt.Println("deep :", deep)
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// 修改原 slice
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original[0] = 999
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fmt.Println("\n修改 original[0] = 999 后:")
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fmt.Println("original:", original) // [999, 2, 3, 4, 5]
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fmt.Println("shallow :", shallow) // [999, 2, 3, 4, 5] ← 被影响！
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fmt.Println("deep :", deep) // [1, 2, 3, 4, 5] ← 不受影响
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}
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// 3. Map 基本使用
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func demoMapUsage() {
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m := make(map[string]int)
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m["apple"] = 5
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m["banana"] = 3
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fmt.Println("map 内容:", m)
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fmt.Println("apple 数量:", m["apple"])
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// 检查 key 是否存在
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if count, ok := m["orange"]; ok {
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fmt.Println("orange 存在，数量:", count)
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} else {
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fmt.Println("orange 不存在")
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}
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// 删除 key
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delete(m, "apple")
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fmt.Println("删除 apple 后:", m)
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}
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// 4. 不安全的并发 map 写入（会导致 panic）
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func demoUnsafeConcurrentMap() {
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m := make(map[int]int)
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var wg sync.WaitGroup
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for i := 0; i < 100; i++ {
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wg.Add(1)
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go func(key int) {
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defer wg.Done()
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m[key] = key * 10 // 并发写 → fatal error: concurrent map writes
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}(i)
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}
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wg.Wait()
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fmt.Println("unsafe map done (should not reach here)")
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}
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// 5. 使用 sync.Map 实现安全并发
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func demoSafeConcurrentMap() {
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var sm sync.Map
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var wg sync.WaitGroup
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for i := 0; i < 100; i++ {
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wg.Add(1)
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go func(key int) {
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defer wg.Done()
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sm.Store(key, key*10)
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}(i)
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}
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wg.Wait()
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// 读取部分值验证
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sm.Range(func(key, value any) bool {
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if key.(int) < 5 { // 只打印前几个
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fmt.Printf("key=%v, value=%v\n", key, value)
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}
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return true // 继续遍历
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})
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}
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