Timeouts {.en}

超时处理 {.zh}

::: {.en} Timeouts are important for programs that connect to external resources or that otherwise need to bound execution time. Implementing timeouts in Go is easy and elegant thanks to channels and select. :::

::: {.zh}

超时处理对于连接到外部资源或需要限制执行时间的程序非常重要。通过通道和通道选择器，在 Go 中实现超时很容易。

:::

package main
import "time"
import "fmt"
func main() {

::: {.en} For our example, suppose we’re executing an external call that returns its result on a channel c1 after 2s. :::

::: {.zh}

对于我们的示例，假设我们正在执行一个外部调用，它在 2s 后在通道 c1 上返回其结果。

:::

    c1 := make(chan string, 1)
    go func() {
        time.Sleep(2 * time.Second)
        c1 <- "result 1"
    }()

::: {.en} Here’s the select implementing a timeout. res := <-c1 awaits the result and <-Time.After awaits a value to be sent after the timeout of 1s. Since select proceeds with the first receive that’s ready, we’ll take the timeout case if the operation takes more than the allowed 1s. :::

::: {.zh}

这是通道选择器实现超时的例子。res := <-c1 等待结果，<-Time.After 等待超时 时间 1 秒后发送的值。由于 select 默认处理第一个 已准备好的接收操作，如果这个操作超过了允许的 1 秒 的话，将会执行超时 case。

:::

    select {
    case res := <-c1:
        fmt.Println(res)
    case <-time.After(1 * time.Second):
        fmt.Println("timeout 1")
    }

::: {.en} If we allow a longer timeout of 3s, then the receive from c2 will succeed and we’ll print the result. :::

::: {.zh}

如果我们允许更长的 3s 超时，将会成功的从 c2 接收到值，并且打印出结果。

:::

    c2 := make(chan string, 1)
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "result 2"
    }()
    select {
    case res := <-c2:
        fmt.Println(res)
    case <-time.After(3 * time.Second):
        fmt.Println("timeout 2")
    }
}

::: {.en} Running this program shows the first operation timing out and the second succeeding. :::

::: {.zh}

运行此程序显示第一个操作超时，第二个成功。

:::

$ go run timeouts.go 
timeout 1
result 2

::: {.en} Using this select timeout pattern requires communicating results over channels. This is a good idea in general because other important Go features are based on channels and select. We’ll look at two examples of this next: timers and tickers. :::

::: {.zh}

使用这个 select 超时方式，需要使用通道传递结果。这对于 一般情况是个好的方式，因为其他重要的 Go 特性是基于通道和 select 的。接下来我们就要看到两个例子：timer 和 ticker。

:::