concurrent

type Runnable interface {
	// Run executes this operation, possibly returning an error if the operation
	// could not be started.  This method is responsible for spawning any necessary
	// goroutines and to ensure WaitGroup.Add() and WaitGroup.Done() are called appropriately.
	// Generally speaking, Run() should be idempotent.
	//
	// The supplied shutdown channel is used to signal any goroutines spawned by this
	// method that they should gracefully exit.  Callers can then use the waitGroup to
	// wait until things have been cleaned up properly.
	Run(waitGroup *sync.WaitGroup, shutdown <-chan struct{}) error
}

type RunnableFunc func(*sync.WaitGroup, <-chan struct{}) error

type RunnableSet []Runnable