饿汉式单例

在导入包的时候直接创建好对象，线程安全，但是会直接占用内存

hungry.go

package single
import "sync"
var h *hungry
func init() {
    h = &hungry{}
}
type hungry struct {
    age int
    rwmux sync.RWMutex
}
func GetHungryInstance() *hungry {
    return h
}
func (h *hungry) IncrementAge() {
    h.rwmux.Lock()
    defer h.rwmux.Unlock()
    h.age++
}
func (h *hungry) GetAge() int {
    h.rwmux.RLock()
    h.rwmux.RUnlock()
    return h.age
}

测试用例: hungry_test.go

package single

import (
    "fmt"
    "sync"
    "testing"
)

func TestGetHungryInstance(t *testing.T) {
    var wg sync.WaitGroup
    wg.Add(20000)
    for i := 0; i < 10000; i++ {
        go func() {
            defer wg.Done()
            GetHungryInstance1()
        }()
        go func() {
            defer wg.Done()
            GetHungryInstance2()
        }()
    }
    wg.Wait()
    h := GetHungryInstance()
    age := h.GetAge()
    fmt.Printf("TestGetHungryInstance: %p\n", h)
    fmt.Println("age: ", age)
}

func GetHungryInstance1() {
    h := GetHungryInstance()
    h.IncrementAge()
    fmt.Printf("GetHungryInstance1: %p\n", h)
}


func GetHungryInstance2() {
    h := GetHungryInstance()
    h.IncrementAge()
    fmt.Printf("GetHungryInstance2: %p\n", h)
}