未初始化的通道如何表现?

问题描述

我有一个结构体，其中包含一个未初始化的通道.

I have a struct that holds a channel that is not initialized.

当我写入它时，例程按预期阻塞，但从未通知读者管道中有东西.

When I write into it, the routine is blocking as expected but the reader is never notified that something is in the pipe.

我很惊讶没有错误，我想知道 Go 在做什么.

I am surprised that there is no error and I am wondering what is doing Go.

在下面的示例中，消息 pushed 和 got it 都没有打印出来.(取消注释初始化，它会像魅力一样工作)

In the example bellow, neither the message pushed nor got it are printed. (Uncomment the intialization and it will work like a charm)

type MyStruct struct {
    over chan bool
}

func main() {
    nonInitialized := &MyStruct{}
    // nonInitialized.over = make(chan bool)
    go func() {
        for i := 0; i < 10; i++ {
            select {
            case <-nonInitialized.over:
                fmt.Println("got it")
            default:
                // proceed
            }
            fmt.Println("do some stuff")
            time.Sleep(10 * time.Millisecond)
        }
        panic("took too long")
    }()
    // push on the non initialized channel
    fmt.Println("pushing")
    nonInitialized.over <- true
    fmt.Println("pushed")
}

这里是游乐场https://play.golang.org/p/76zrCuoeoh

(我知道我应该初始化通道，这不是问题的目的，我想知道使用未初始化的通道在 Go 中发生了什么.)

(I know I should initialize the channel, this is not the purpose of the question, I want to know what is happening in Go with non initialized channels.)

推荐答案

的未初始化"字段或变量频道类型将具有所有频道类型的零值，即nil.因此，让我们检查 nil 通道或对它的操作的行为.

An "uninitialized" field or variable of channel type will have the zero value of all channel types which is nil. So let's examine how a nil channel or operations on it behave.

值得在一篇文章中收集频道公理:

• 在 nil 频道上发送永远阻塞(规范:发送语句)
• 来自 nil 频道的接收将永远阻塞(规范:接收运算符)
• 发送到关闭的通道恐慌(规范:发送语句)
• 来自封闭通道的接收立即返回零值(规范:接收运算符)

• a send on a nil channel blocks forever (Spec: Send statements)
• a receive from a nil channel blocks forever (Spec: Receive operator)
• a send to a closed channel panics (Spec: Send statements)
• a receive from a closed channel returns the zero value immediately (Spec: Receive operator)

在 nil 通道的情况下阻塞的原因:如果通道值为 nil，则没有人引用它，因此没有人准备好接收从它(我们想要发送的)；或者在上面发送任何东西(我们会从中收到什么).

Reasoning for blocking in case of nil channels: if a channel value is nil, no one has a reference to it, so no one will ever be ready to receive from it (what we want to send); or send anything on it (what we would receive from it).

您可以在 Dave Cheney:Channel Axioms 中阅读有关此的进一步推理和更多详细信息.

为了完整性:

• 关闭 nil 频道会导致 运行时恐慌(就像关闭已经关闭的频道一样).
• 长度和容量 nil 频道是 0;根据 nil 切片和具有 0 长度和容量的映射.

• Closing a nil channel causes a run-time panic (just like closing an already closed channel).
• Length and capacity of a nil channel is 0; in accordance with nil slices and maps having 0 length and capacity.

推理:关闭"是一种状态，但nil通道不能有状态(只有一个nil通道，而关闭"和一个用于未关闭"通道).并且在 nil 通道中没有元素排队(所以 len = 0)，并且它没有缓冲容量(所以 cap = 0).

Reasoning: "closed" is a state, but a nil channel cannot have a state (there is only one nil channel, and not one for "closed" and one for "not closed" channel). And there are no elements queued in a nil channel (so len = 0), and it does not have a buffer capacity (so cap = 0).

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