go的context

• 在context中存储数据
• 使用context来管理协程

context的本质

type Context interface {
	Deadline() (time.Time, bool)
	Err() error
	value(key any) any
	Done() <-chan struct{}
}

emptyContext

// An emptyCtx is never canceled, has no values, and has no deadline. It is not
// struct{}, since vars of this type must have distinct addresses.
type emptyCtx int

func (*emptyCtx) Deadline() (deadline time.Time, ok bool) {
	return
}

func (*emptyCtx) Done() <-chan struct{} {
	return nil
}

func (*emptyCtx) Err() error {
	return nil
}

func (*emptyCtx) Value(key any) any {
	return nil
}