为什么在 Golang 中发送超过缓冲通道大小的值会导致死锁错误？

Question

// By default channels are _unbuffered_, meaning that they

// will only accept sends (`chan <-`) if there is a

// corresponding receive (`<- chan`) ready to receive the

// sent value. _Buffered channels_ accept a limited

// number of  values without a corresponding receiver for

// those values.

package main

import "fmt"

func main() {

    // Here we `make` a channel of strings buffering up to

    // 2 values.

    messages := make(chan string, 2)

    // Because this channel is buffered, we can send these

    // values into the channel without a corresponding

    // concurrent receive.

    messages <- "buffered"

    messages <- "channel"

    messages <- "channel1" //I added this. 

    // Later we can receive these two values as usual.

    fmt.Println(<-messages)

    fmt.Println(<-messages)

}

它抛出的错误：

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan send]:

main.main()

    /tmp/sandbox795158698/prog.go:23 +0x8d

问题：

1. 我们不能发送比缓冲区大小更多的值吗？

2. 为什么错误说“所有 goroutines 都在睡觉 - 死锁！” 当代码中没有 goroutines 时？

3. 为什么会出现这种僵局？请解释？

Answer 1

写入完整通道的尝试将被阻塞，直到其他一些 goroutine 从中读取。在您的程序中，没有其他 goroutines。因此，当您写入完整通道时，主 goroutine 会阻塞，并且由于没有其他 goroutine，因此主 goroutine 不可能继续进行。那是一个僵局。

Answer 2

添加到上述答案： https ://stackoverflow.com/a/61512364/4106031package mainimport (&nbsp; &nbsp; "fmt"&nbsp; &nbsp; "github.com/practo/klog/v2"&nbsp; &nbsp; "os"&nbsp; &nbsp; "os/signal"&nbsp; &nbsp; "syscall"&nbsp; &nbsp; "time")func producer(msgBuf chan<- string) {&nbsp; &nbsp; for i := 0; ; i++ {&nbsp; &nbsp; &nbsp; &nbsp; fmt.Printf("sent: %d\n", i)&nbsp; &nbsp; &nbsp; &nbsp; msgBuf <- fmt.Sprintf("%d", i)&nbsp; &nbsp; &nbsp; &nbsp; time.Sleep(1 * time.Second)&nbsp; &nbsp; }}func process(msgBuf <-chan string) {&nbsp; &nbsp; time.Sleep(10 * time.Second)&nbsp; &nbsp; for {&nbsp; &nbsp; &nbsp; &nbsp; select {&nbsp; &nbsp; &nbsp; &nbsp; case msg := <-msgBuf:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fmt.Printf("processing: %v\n", msg)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; time.Sleep(10 * time.Second)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fmt.Printf("processed: %v\n", msg)&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}func main() {&nbsp; &nbsp; msgBuf := make(chan string, 2)&nbsp; &nbsp; go producer(msgBuf)&nbsp; &nbsp; go process(msgBuf)&nbsp; &nbsp; sigterm := make(chan os.Signal, 1)&nbsp; &nbsp; signal.Notify(sigterm, syscall.SIGINT, syscall.SIGTERM)&nbsp; &nbsp; for {&nbsp; &nbsp; &nbsp; &nbsp; select {&nbsp; &nbsp; &nbsp; &nbsp; default:&nbsp; &nbsp; &nbsp; &nbsp; case <-sigterm:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; klog.Info("SIGTERM signal received")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; os.Exit(1)&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}当您在不同的 go 例程中运行它们时，这不会导致死锁。