Golang - 按值锁定

Question

我正在编写一个接受 tableName 值和 updEpoch 值的 golang api，即：

curl -F "tableName=abc" -F "updEpoch=123" myhost:8080/singleroute
curl -F "tableName=abc" -F "updEpoch=456" myhost:8080/singleroute
curl -F "tableName=def" -F "updEpoch=123" myhost:8080/singleroute
curl -F "tableName=def" -F "updEpoch=345" myhost:8080/singleroute

我想允许并行处理多个不同的 tableName 请求，但同时每个 tableName 只能处理 1 个请求。所以在上面的例子中，如果同时触发了 4 个以上的请求，那么第一个和第三个应该能够同时运行（作为唯一的 tableNames），但是第二个只会在第一个完成后开始，第四个只会在第三个完成后开始。当我研究互斥锁时，似乎没有任何例子适合这种情况，我不想在代码中的任何地方对 abc/def.etc 进行硬编码，因为相同的规则应该适用于任何任意 tableName。

我的猜测基于 Crowman 的帮助：

package main

import (
    "fmt"
    "sync"
    "time"
    "http"
)
km := KeyedMutex{}
type KeyedMutex struct {
    mutexes sync.Map // Zero value is empty and ready for use
}

func (m *KeyedMutex) Lock(key string) func() {
    value, _ := m.mutexes.LoadOrStore(key, &sync.Mutex{})
    mtx := value.(*sync.Mutex)
    mtx.Lock()

    return func() { mtx.Unlock() }
}

func myFunc(key string, data string) string {
  //do some stuff
  return "done for key:"+key+", data: "+data
}

func main() {
    key := //some form value sent to my api 
    data := //some form value sent to my api 
    unlock := km.Lock(key)
    defer unlock()
    retVal := myFunc(key, data)
}

Answer 1

您可以sync.Map将表名用作键，将 a*sync.Mutex用作值。

例如：

package main

import (
    "fmt"
    "sync"
    "time"
)

type KeyedMutex struct {
    mutexes sync.Map // Zero value is empty and ready for use
}

func (m *KeyedMutex) Lock(key string) func() {
    value, _ := m.mutexes.LoadOrStore(key, &sync.Mutex{})
    mtx := value.(*sync.Mutex)
    mtx.Lock()

    return func() { mtx.Unlock() }
}

func main() {
    wg := sync.WaitGroup{}
    km := KeyedMutex{}

    for _, job := range []struct {
        key  string
        data string
    }{
        {key: "abc", data: "123"},
        {key: "abc", data: "456"},
        {key: "def", data: "123"},
        {key: "def", data: "456"},
    } {
        var job = job
        wg.Add(1)

        go func() {
            defer wg.Done()

            unlock := km.Lock(job.key)
            defer unlock()

            fmt.Printf("%s:%s mutex acquired\n", job.key, job.data)
            time.Sleep(time.Second * 1) // To ensure some goroutines visibly block
            fmt.Printf("%s:%s done\n", job.key, job.data)
        }()
    }

    wg.Wait()
}

带有示例输出：

crow@mac:$ ./mut
def:456 mutex acquired
abc:456 mutex acquired
abc:456 done
def:456 done
abc:123 mutex acquired
def:123 mutex acquired
def:123 done
abc:123 done
crow@mac:$

显示具有不同表名的请求立即获得互斥锁，但具有相同表名的请求被序列化。

Answer 2

您可以创建包级别var map[string]*sync.Mutex并锁定将通过表名称获取/创建的相应互斥体。