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各个组件作为一个整体运行，并有序地结束
假设我们有四个 Go routine 组件，如图所示，分别是运行一个状态机 sm.Run 、启动一个 HTTP 服务器、执行定时任务 cronJobs(sm) 读取状态机状态、和运行信号监听器。每个 Go routine 组件互相独立运行。
Group 是一组 actor，通过调用 Add 方法将 actor 添加到 Group 中. 每个 actor 有两个方法：execute 和 interrupt。execute 完成 Go routine 的计算任务，interrupt 结束 Go routine 并退出。
// github.com/oklog/run@v1.1.0/group.go
// Group collects actors (functions) and runs them concurrently.
// When one actor (function) returns, all actors are interrupted.
// The zero value of a Group is useful.
type Group struct {
actors []actor
}
type actor struct {
execute func() error
interrupt func(error)
}添加
// Add an actor (function) to the group. Each actor must be pre-emptable by an
// interrupt function. That is, if interrupt is invoked, execute should return.
// Also, it must be safe to call interrupt even after execute has returned.
//
// The first actor (function) to return interrupts all running actors.
// The error is passed to the interrupt functions, and is returned by Run.
func (g *Group) Add(execute func() error, interrupt func(error)) {
g.actors = append(g.actors, actor{execute, interrupt})
}运行
调用 Run 方法后会启动所有 Go routine（或者称为 actor），并等待第一个结束的 Go routine（无论正常退出或因为异常终止）。一旦捕获到第一个结束信号，会依次结束其他 Go routine 直到所有 Go routine 完全退出。
// Run all actors (functions) concurrently.
// When the first actor returns, all others are interrupted.
// Run only returns when all actors have exited.
// Run returns the error returned by the first exiting actor.
func (g *Group) Run() error {
if len(g.actors) == 0 {
return nil
}
// Run each actor.
errors := make(chan error, len(g.actors))
for _, a := range g.actors {
go func(a actor) {
errors <- a.execute()
}(a)
}
// Wait for the first actor to stop.
err := <-errors
// Signal all actors to stop.
for _, a := range g.actors {
a.interrupt(err)
}
// Wait for all actors to stop.
for i := 1; i < cap(errors); i++ {
<-errors
}
// Return the original error.
return err
}