[TOC] ## 7、动态保活Worker工作池设计 ### 一、我们如何知道一个Goroutine已经死亡？ 实际上，Go语言并没有给我们暴露如何知道一个Goroutine是否存在的接口，如果要证明一个Go是否存在，可以在子Goroutine的业务中，定期写向一个keep live的Channel，然后主Goroutine来发现当前子Go的状态。Go语言在对于Go和Go之间没有像进程和线程一样有强烈的父子、兄弟等关系，每个Go实际上对于调度器都是一个独立的，平等的执行流程。 >PS: 如果你是监控子线程、子进程的死亡状态，就没有这么简单了，这里也要感谢go的调度器给我们提供的方便，我们既然用Go，就要基于Go的调度器来实现该模式。 那么，我们如何做到一个Goroutine已经死亡了呢？ #### 子Goroutine 可以通过给一个被监控的Goroutine添加一个`defer` ，然后`recover()` 捕获到当前Goroutine的异常状态，最后给主Goroutine发送一个死亡信号，通过`Channel`。 #### 主Goroutine 在`主Goroutine`上，从这个`Channel`读取内容，当读到内容时，就重启这个`子Goroutine`，当然`主Goroutine`需要记录`子Goroutine`的`ID`，这样也就可以针对性的启动了。 ### 二、代码实现 我们这里以一个工作池的场景来对上述方式进行实现。 `WorkerManager`作为`主Goroutine`, `worker`作为子`Goroutine` > WorkerManager ```go type WorkerManager struct { //用来监控Worker是否已经死亡的缓冲Channel workerChan chan *worker // 一共要监控的worker数量 nWorkers int } //创建一个WorkerManager对象 func NewWorkerManager(nworkers int) *WorkerManager { return &WorkerManager{ nWorkers:nworkers, workerChan: make(chan *worker, nworkers), } } //启动worker池，并为每个Worker分配一个ID，让每个Worker进行工作 func (wm *WorkerManager)StartWorkerPool() { //开启一定数量的Worker for i := 0; i < wm.nWorkers; i++ { i := i wk := &worker{id: i} go wk.work(wm.workerChan) } //启动保活监控 wm.KeepLiveWorkers() } //保活监控workers func (wm *WorkerManager) KeepLiveWorkers() { //如果有worker已经死亡 workChan会得到具体死亡的worker然后 打出异常，然后重启 for wk := range wm.workerChan { // log the error fmt.Printf("Worker %d stopped with err: [%v] \n", wk.id, wk.err) // reset err wk.err = nil // 当前这个wk已经死亡了，需要重新启动他的业务 go wk.work(wm.workerChan) } } ``` >worker ```go type worker struct { id int err error } func (wk *worker) work(workerChan chan<- *worker) (err error) { // 任何Goroutine只要异常退出或者正常退出 都会调用defer 函数，所以在defer中想WorkerManager的WorkChan发送通知 defer func() { //捕获异常信息，防止panic直接退出 if r := recover(); r != nil { if err, ok := r.(error); ok { wk.err = err } else { wk.err = fmt.Errorf("Panic happened with [%v]", r) } } else { wk.err = err } //通知 主 Goroutine，当前子Goroutine已经死亡 workerChan <- wk }() // do something fmt.Println("Start Worker...ID = ", wk.id) // 每个worker睡眠一定时间之后，panic退出或者 Goexit()退出 for i := 0; i < 5; i++ { time.Sleep(time.Second*1) } panic("worker panic..") //runtime.Goexit() return err } ``` ### 三、测试 >main ```go func main() { wm := NewWorkerManager(10) wm.StartWorkerPool() } ``` 结果： ```bash $ go run workmanager.go Start Worker...ID = 2 Start Worker...ID = 1 Start Worker...ID = 3 Start Worker...ID = 4 Start Worker...ID = 7 Start Worker...ID = 6 Start Worker...ID = 8 Start Worker...ID = 9 Start Worker...ID = 5 Start Worker...ID = 0 Worker 9 stopped with err: [Panic happened with [worker panic..]] Worker 1 stopped with err: [Panic happened with [worker panic..]] Worker 0 stopped with err: [Panic happened with [worker panic..]] Start Worker...ID = 9 Start Worker...ID = 1 Worker 2 stopped with err: [Panic happened with [worker panic..]] Worker 5 stopped with err: [Panic happened with [worker panic..]] Worker 4 stopped with err: [Panic happened with [worker panic..]] Start Worker...ID = 0 Start Worker...ID = 2 Start Worker...ID = 4 Start Worker...ID = 5 Worker 7 stopped with err: [Panic happened with [worker panic..]] Worker 8 stopped with err: [Panic happened with [worker panic..]] Worker 6 stopped with err: [Panic happened with [worker panic..]] Worker 3 stopped with err: [Panic happened with [worker panic..]] Start Worker...ID = 3 Start Worker...ID = 6 Start Worker...ID = 8 Start Worker...ID = 7 ... ... ``` 我们会发现，无论子Goroutine是因为 panic()异常退出，还是Goexit()退出，都会被主Goroutine监听到并且重启。主要我们就能够起到保活的功能了. 当然如果线程死亡？进程死亡？我们如何保证？ 大家不用担心，我们用Go开发实际上是基于Go的调度器来开发的，进程、线程级别的死亡，会导致调度器死亡，那么我们的全部基础框架都将会塌陷。那么就要看线程、进程如何保活啦，不在我们Go开发的范畴之内了。