Task 4: Find errors in code with channels and goroutines (double closing of a channel)

A double channel close error in Go occurs when the same channel is closed more than once, leading to a panic.

A typical example of this error:

dataCh := make(chan int)

// Goroutine that closes the channel
go func() {
    for i := 0; i < 5; i++ {
        dataCh <- i
    }
    close(dataCh) // Closing the channel
}()

// Trying to close the channel elsewhere again
close(dataCh) // PANIC: closing an already closed channel

How to avoid:

• Only the sender (writer) should close the channel.
• Receivers should not close the channel.
• If multiple goroutines write to the channel, synchronization of closing (e.g., using sync.WaitGroup) is necessary.

Example of correct usage:

func producer(ch chan<- int) {
    for i := 0; i < 5; i++ {
        ch <- i
    }
    close(ch) // Close the channel only here
}

func consumer(ch <-chan int) {
    for val := range ch {
        fmt.Println(val)
    }
}

func main() {
    ch := make(chan int)
    go producer(ch)
    consumer(ch)
}

Thus, to avoid double closing, it is essential to clearly define responsibility for closing the channel and use synchronization when necessary.