Range Over Channel Without Close (ARCH5036)

Key go.async.range-chan-no-close · Severity warning · Category async

Ranging over a channel that is never closed anywhere in the package leaves the range loop blocked forever after the last value. The producer side must close the channel once it is done sending.

Incorrect

func Sum(nums []int) int {
  ch := make(chan int)
  go func() {
    for _, n := range nums {
      ch <- n
    }
    // missing close
  }()
  total := 0
  for v := range ch { // blocks after the last value
    total += v
  }
  return total
}

Correct

func Sum(nums []int) int {
  ch := make(chan int)
  go func() {
    for _, n := range nums {
      ch <- n
    }
    close(ch)
  }()
  total := 0
  for v := range ch {
    total += v
  }
  return total
}

Fix

Close the channel with close(ch) once the producing goroutine is done sending.