golang Map 并发安全的几个点

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有几个坑，需要注意一下

实现1

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//
// map_safe.go
// Copyright (C) 2018 chentao <chentao@chentaos-MacBook-Pro.local>
//
// Distributed under terms of the MIT license.
//
package main
import (
	"fmt"
	"sync"
	"time"
)
type ctr struct {
	sync.RWMutex
	m map[string]int
}
func main() {
	counter := &ctr{m: make(map[string]int)}
	for i := 0; i < 10; i++ {
		go bc(counter)
	}
	//for i := 0; i < 10; i++ {
	//	go set(counter, i*10)
	//}
	//for i := 0; i < 10; i++ {
	//	go get(counter)
	//}
	time.Sleep(time.Second * 2)
}
func bc(counter *ctr) {
	for i := 0; i < 10; i++ {
		go set(counter, i)
	}
	for i := 0; i < 10; i++ {
		go get(counter)
	}
}
// counter 这里必须是引用
func set(counter *ctr, v int) {
	counter.Lock()
	defer func() {
		counter.Unlock()
		fmt.Printf("set unlock mutex addr %p \n", &counter.RWMutex)
		fmt.Printf("set unlock count addr %p \n", &counter.m)
		fmt.Printf("set unlock all addr %p \n", &counter)
	}()
	//counter.m["some_key"] = v
	counter.m["some_key"] = counter.m["some_key"] + v
	//time.Sleep(time.Millisecond * 10)
	fmt.Println("some_key set:", counter.m["some_key"])
}
func get(counter *ctr) {
	counter.RLock()
	defer func() {
		counter.RUnlock()
		fmt.Printf("get unlock mutex addr %p \n", &counter.RWMutex)
		fmt.Printf("get unlock count addr %p \n", &counter.m)
		fmt.Printf("get unlock all addr %p \n", &counter)
	}()
	n := counter.m["some_key"]
	fmt.Println("some_key get:", n)
}

实现2

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//
// map_safe.go
// Copyright (C) 2018 chentao <chentao@chentaos-MacBook-Pro.local>
//
// Distributed under terms of the MIT license.
//
package main
import (
	"fmt"
	"sync"
	"time"
	"unsafe"
)
type ctr2 struct {
	sync.RWMutex
	m map[string]int
}
func main() {
	counter := ctr2{m: make(map[string]int)}
	for i := 0; i < 10; i++ {
		go counter.bc()
	}
	//for i := 0; i < 10; i++ {
	//	go set(counter, i*10)
	//}
	//for i := 0; i < 10; i++ {
	//	go get(counter)
	//}
	time.Sleep(time.Second * 2)
}
// counter这里都OK
func (counter *ctr2) bc() {
	for i := 0; i < 10; i++ {
		go counter.set(i)
	}
	for i := 0; i < 10; i++ {
		go counter.get()
	}
}
func (counter *ctr2) set(v int) {
	counter.Lock()
	defer func() {
		counter.Unlock()
		fmt.Printf("set unlock mutex addr %p \n", &counter.RWMutex)
		fmt.Printf("set unlock count addr %p \n", &counter.m)
		fmt.Printf("set unlock all addr %p \n", &(*counter))
		fmt.Printf("set unlock all addr %p \n", unsafe.Pointer(counter))
		fmt.Printf("set unlock all addr %p \n", counter)
	}() // 注意这几个对象引用和地址的区分
	//counter.m["some_key"] = v
	counter.m["some_key"] = counter.m["some_key"] + v
	//time.Sleep(time.Millisecond * 10)
	fmt.Println("some_key set:", counter.m["some_key"])
}
func (counter *ctr2) get() {
	counter.RLock()
	defer func() {
		counter.RUnlock()
		fmt.Printf("get unlock mutex addr %p \n", &counter.RWMutex)
		fmt.Printf("get unlock count addr %p \n", &counter.m)
		fmt.Printf("get unlock all addr %p \n", &(*counter))
		fmt.Printf("get unlock all addr %p \n", unsafe.Pointer(counter))
		fmt.Printf("get unlock all addr %p \n", counter)
	}()
	n := counter.m["some_key"]
	fmt.Println("some_key get:", n)
}