每日一库之134：fsm（基有限状态机库）

开发中，我们经常会遇到这种情况，服务模块有多种状态，它们有一定的顺序，先后执行，逐步切换。这时，fsm这个库可以帮助我们更好的管理多个状态。

fsm库，它主要基于两个FSM实现，增加了golang版本的实现：

• Javascript Finite State Machine, https://github.com/jakesgordon/javascript-state-machine
• Fysom for Python, https://github.com/oxplot/fysom (forked at https://github.com/mriehl/fysom)

简单举例

package main
import (
 "fmt"
 "github.com/looplab/fsm"
)
func enterState(e *fsm.Event) {
 fmt.Printf("event: %s, from:%s to %s\n", e.Event, e.Src, e.Dst)
}
func main() {
 f := fsm.NewFSM(
  "sleeping",
  fsm.Events{
   {Name: "eat", Src: []string{"sleeping"}, Dst: "eating"},
   {Name: "work", Src: []string{"eating"}, Dst: "working"},
   {Name: "sleep", Src: []string{"working"}, Dst: "sleeping"},
  },
  fsm.Callbacks{
   "enter_state": func(e *fsm.Event) { enterState(e) },
  },
 )
err := f.Event("eat")
 if err != nil {
  fmt.Println(err)
 }
err = f.Event("work")
 if err != nil {
  fmt.Println(err)
 }
err = f.Event("sleep")
 if err != nil {
  fmt.Println(err)
 }
}

执行，控制台输出如下：

$ go run test.go
event: eat, from:sleeping to eating
event: work, from:eating to working
event: sleep, from:working to sleeping

结构体举例

package main
import (
 "fmt"
 "github.com/looplab/fsm"
)
type Door struct {
 To  string
 FSM *fsm.FSM
}
func NewDoor(to string) *Door {
 d := &Door{
  To: to,
 }
d.FSM = fsm.NewFSM(
  "closed",
  fsm.Events{
   {Name: "open", Src: []string{"closed"}, Dst: "open"},
   {Name: "close", Src: []string{"open"}, Dst: "closed"},
  },
  fsm.Callbacks{
   "enter_state": func(e *fsm.Event) { d.enterState(e) },
  },
 )
return d
}
func (d Door) enterState(e fsm.Event) {
 fmt.Printf("The door to %s, event: %s, from:%s to %s\n", d.To, e.Event, e.Src, e.Dst)
}
func main() {
 door := NewDoor("zhang san")
err := door.FSM.Event("open")
 if err != nil {
  fmt.Println(err)
 }
err = door.FSM.Event("close")
 if err != nil {
  fmt.Println(err)
 }
}

执行，控制台输出如下：

$ go run test.go
The door to zhang san, event: open, from:closed to open
The door to zhang san, event: close, from:open to closed

总结

fsm 是一个非常简单，好用的状态机管理库。如果你各种状态切换的需求，不妨试试看，相信一定会喜欢上的！

参考资料

• https://github.com/looplab/fsm