Go 使用互斥锁(sync.Mutex)实现线程安全的内存本地缓存(LocalCache)

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禅与计算机程序设计艺术 2022-06-07 17:38:23 ©著作权

文章标签 golang 缓存开发语言后端 ide 文章分类 Go语言后端开发

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本地缓存实现

var cache = struct { // 声明 struct 字面量 cahce (匿名结构体)
    sync.Mutex                   // 互斥锁, 内嵌 Struct
    caches     map[string]string // kv 内存存储
}{
    caches: make(map[string]string), // 初始化 kv 存储
}

// GetCache safe get memory cache
func GetCache(key string) string {
    cache.Lock()           // 锁住
    v := cache.caches[key] // 获取缓存值
    defer cache.Unlock()   // 释放锁
    return v
}

// PutCache safe put memory cache
func PutCache(key string, val string) {
    cache.Lock()            // 锁住
    cache.caches[key] = val // 设置缓存值
    defer cache.Unlock()    // 释放锁
}

func main() {
    for i := 0; i < 10; i++ {
        PutCache(fmt.Sprintf("key%d", i), fmt.Sprintf("value%d", i))
    }
    var v = GetCache("key1")
    fmt.Println(v) // value1
}

sync.Mutex 说明

核心实现: CompareAndSwap

// Package sync provides basic synchronization primitives such as mutual
// exclusion locks. Other than the Once and WaitGroup types, most are intended
// for use by low-level library routines. Higher-level synchronization is
// better done via channels and communication.
//
// Values containing the types defined in this package should not be copied.
package sync

import (
    "internal/race"
    "sync/atomic"
    "unsafe"
)

func throw(string) // provided by runtime

// A Mutex is a mutual exclusion lock.
// The zero value for a Mutex is an unlocked mutex.
//
// A Mutex must not be copied after first use.
type Mutex struct {
    state int32
    sema  uint32
}

// A Locker represents an object that can be locked and unlocked.
type Locker interface {
    Lock()
    Unlock()
}

const (
    mutexLocked = 1 << iota // mutex is locked
    mutexWoken
    mutexStarving
    mutexWaiterShift = iota

    // Mutex fairness.
    //
    // Mutex can be in 2 modes of operations: normal and starvation.
    // In normal mode waiters are queued in FIFO order, but a woken up waiter
    // does not own the mutex and competes with new arriving goroutines over
    // the ownership. New arriving goroutines have an advantage -- they are
    // already running on CPU and there can be lots of them, so a woken up
    // waiter has good chances of losing. In such case it is queued at front
    // of the wait queue. If a waiter fails to acquire the mutex for more than 1ms,
    // it switches mutex to the starvation mode.
    //
    // In starvation mode ownership of the mutex is directly handed off from
    // the unlocking goroutine to the waiter at the front of the queue.
    // New arriving goroutines don't try to acquire the mutex even if it appears
    // to be unlocked, and don't try to spin. Instead they queue themselves at
    // the tail of the wait queue.
    //
    // If a waiter receives ownership of the mutex and sees that either
    // (1) it is the last waiter in the queue, or (2) it waited for less than 1 ms,
    // it switches mutex back to normal operation mode.
    //
    // Normal mode has considerably better performance as a goroutine can acquire
    // a mutex several times in a row even if there are blocked waiters.
    // Starvation mode is important to prevent pathological cases of tail latency.
    starvationThresholdNs = 1e6
)

// Lock locks m.
// If the lock is already in use, the calling goroutine
// blocks until the mutex is available.
func (m *Mutex) Lock() {
    // Fast path: grab unlocked mutex.
    if atomic.CompareAndSwapInt32(&m.state, 0, mutexLocked) {
        if race.Enabled {
            race.Acquire(unsafe.Pointer(m))
        }
        return
    }
    // Slow path (outlined so that the fast path can be inlined)
    m.lockSlow()
}



// Unlock unlocks m.
// It is a run-time error if m is not locked on entry to Unlock.
//
// A locked Mutex is not associated with a particular goroutine.
// It is allowed for one goroutine to lock a Mutex and then
// arrange for another goroutine to unlock it.
func (m *Mutex) Unlock() {
    if race.Enabled {
        _ = m.state
        race.Release(unsafe.Pointer(m))
    }

    // Fast path: drop lock bit.
    new := atomic.AddInt32(&m.state, -mutexLocked)
    if new != 0 {
        // Outlined slow path to allow inlining the fast path.
        // To hide unlockSlow during tracing we skip one extra frame when tracing GoUnblock.
        m.unlockSlow(new)
    }
}

...

内嵌 struct

通常我们使用"有名"的 struct 嵌套如下:

package main
 
import "fmt"
 
type People struct{
    name string
    age int8
}
 
type Employee struct{
    profile *People
    salary float32
}
func main() {
   p := &People{
           name: "Mr.Lee",
           age: 32,
       }
   e := &Employee{
       profile: p,
       salary: 600000,
   }
    fmt.Println("Hello world!", e.profile.name)
}

go语言中虽然没有继承,但是可以结构内嵌,达到类似继承的效果:

type Info struct {
    sex int
    name string
    age int
    address string
}
 
type User struct{
    like string
    Info
}
 
type Admin struct {
    unlike string
    Info
}
 
user:= User{}
user.sex=0
user.address="广州市"
user.like="游戏"
f.Println(user)
    
    
admin:= Admin{Info:Info{sex:1}}//还可以这样声明一些属性值,因为Info是结构体,匿名,所以需要这样声明
admin.address="广州市"
admin.unlike="游戏"
f.Println(admin)