如何在 Go 中安全地关闭一个 chan chan T？

Question

我正在实施一个简单的工作池算法，其中 1 个 Sender（调度程序）将作业发送到 M（Worker）go 例程。为此，它使用一个通道的通道来为第一个空闲的工作人员分配一个可用的工作：

// builds the pool
func NewWorkerPool(maxWorkers int) WorkerPool {
    pool := make(chan chan Job, maxWorkers)
    workers := make([]Worker, 0)
    return WorkerPool{
        WorkerPool: pool,
        Workers: workers,
        maxWorkers: maxWorkers,
        waitGroup: sync.WaitGroup{}}
}

// Starts the WorkerPool
func (p *WorkerPool) Run(queue chan Job) {
    w := p.waitGroup

    // starting n number of workers
    for i := 0; i < p.maxWorkers; i++ {
        worker := NewWorker(p.WorkerPool)
        p.Workers = append(p.Workers, worker)
        w.Add(1)
        worker.Start(&w)
    }

    go p.dispatch(queue)
}

// dispatches a job to be handled by an idle Worker of the pool
func (p *WorkerPool) dispatch(jobQueue chan Job) {
    for {
        select {
        case job := <-jobQueue:
            // a model request has been received
            go func(job Job) {
                // try to obtain a worker model channel that is available.
                // this will block until a worker is idle
                jobChannel := <-p.WorkerPool

                // dispatch the model to the worker model channel
                jobChannel <- job
            }(job)
        }
    }
}


// checks if a Worker Pool is open or closed - If we can recieve on the channel then it is NOT closed
func (p *WorkerPool) IsOpen() bool {
    _, ok := <-p.WorkerPool
    return ok
}

worker 启动和停止方法

// Start method starts the run loop for the worker, listening for a quit channel in
// case we need to stop it
func (w Worker) Start(wg *sync.WaitGroup) {
    go func() {
        defer wg.Done()
        for {
            // register the current worker into the worker queue.
            w.WorkerPool <- w.JobChannel

            select {
            case job := <-w.JobChannel:
                // we have received a work request.
                result := job.Run()
                job.ReturnChannel <- result

                // once result is returned close the job output channel
                close(job.ReturnChannel)

            case <-w.quit:
                // we have received a signal to stop
                return
            }
        }
    }()
}

// Stop signals the worker to stop listening for work requests.
func (w Worker) Stop() {
    go func() {
        w.quit <- true
    }()
}

现在我尝试使用以下方法关闭池，我使用 sync.WaitGroup 以等待所有工作人员关闭：

// stops the Pool
func (p *WorkerPool) Stop() bool {
    // stops all workers
    for _, worker := range p.Workers {
        worker.Stop()
    }
    p.waitGroup.Wait() //Wait for the goroutines to shutdown

    close(p.WorkerPool)

    more := p.IsOpen()

    fmt.Printf(" more? %t", more)

    return ok
}

//打印更多？真

即使我等待工作人员退出并稍后调用关闭（p.WorkerPool）我仍然打开了通道，在这种情况下缺少什么，如何相应地关闭通道？

Answer 1

关闭通道表示不再向其发送任何值。这对于向通道的接收者传达完成信息很有用。

通道中的数据仍然存在，您可能需要关闭通道，然后删除其中的所有通道，如下所示

// Stop stops the Pool and free all the channels
func (p *WorkerPool) Stop() bool {
    // stops all workers
    for _, worker := range p.Workers {
        worker.Stop()
    }
    p.waitGroup.Wait() //Wait for the goroutines to shutdown
    close(p.WorkerPool)
    for channel := range p.WorkerPool {
        fmt.Println("Freeing channel") //remove all the channels
    }
    more := p.IsOpen()
    fmt.Printf(" more? %t", more)

    return ok
}

顺便说一句，不能使用 _, ok <- 来检查频道是否关闭。我会为函数建议一个不同的名称

如何在 Go 中安全地关闭一个 chan chan T？

how to safely close a chan chan T in Go?

multithreading

go

synchronization

shutdown