I need a non blocking channel with dynamic buffer for a project so I wrote this code.
Here is the type declaration:
//receiver is the receiver of the non blocking channel
type receiver struct {
Chan <-chan string
list *[]string
mutex sync.RWMutex
}
//Clear sets the buffer to 0 elements
func (r *receiver) Clear() {
r.mutex.Lock()
*r.list = (*r.list)[:0]
r.mutex.Unlock()
//Discards residual content
if len(r.Chan) == 1 {
<-r.Chan
}
}
Constructor:
//NewNonBlockingChannel returns the receiver & sender of a non blocking channel
func NewNonBlockingChannel() (*receiver, chan<- string) {
//Creates the send and receiver channels and the buffer
send := make(chan string)
recv := make(chan string, 1)
list := make([]string, 0, 20)
r := &receiver{Chan: recv, list: &list}
go func() {
for {
//When the receiver is empty sends the next element from the buffer
if len(recv) == 0 && len(list) > 0 {
r.mutex.Lock()
recv <- list[len(list)-1]
list = list[:len(list)-1]
r.mutex.Unlock()
}
select {
//Adds the incoming elements to the buffer
case s := <-send:
r.mutex.Lock()
list = append(list, s)
r.mutex.Unlock()
//default:
}
}
}()
return r, send
}
And the toy test in the main:
func main() {
recv, sender := NewNonBlockingChannel()
//send data to the channel
go func() {
for i := 0; i < 5; i++ {
sender <- "Hi"
}
time.Sleep(time.Second)
for i := 0; i < 5; i++ {
sender <- "Bye"
}
}()
time.Sleep(time.Millisecond * 70) //waits to receive every "Hi"
recv.Clear()
for data := range recv.Chan {
println(data)
}
}
When I tested it and a deadlock happened in the select statement when I receive from the sender "case s := <-send:" but when I move the conditional block which sends the next buffered string into the select statement everything works perfectly:
go func() {
for {
select {
//Adds the incoming elements to the buffer
case s := <-send:
r.mutex.Lock()
list = append(list, s)
r.mutex.Unlock()
default:
//When the receiver is empty sends the next element from the buffer
if len(recv) == 0 && len(list) > 0 {
r.mutex.Lock()
recv <- list[len(list)-1]
list = list[:len(list)-1]
r.mutex.Unlock()
}
}
}
}()
I'd like to know why.