In the following code I am trying to spawn MaxOutstanding
number of handlers. Each handler loops over items in the queue queue
and prints them out, I also write true
to the done
channel.
In my main function, I start the handlers and write 9 elements to the queue
and wait for the 1st element to be written to the done
queue.
package main
import "fmt"
type Request struct {
int32
}
var MaxOutstanding = 5
func handle(queue chan *Request, i int, done chan bool) {
for r := range queue {
fmt.Println(i, "---", r)
done <- true
}
}
func Serve(clientRequests chan *Request, quit, done chan bool) {
// Start handlers
for i := 0; i < MaxOutstanding; i++ {
go handle(clientRequests, i, done)
}
<-quit // Wait to be told to exit.
}
func main() {
clientRequests := make(chan *Request)
quit := make(chan bool)
done := make(chan bool)
go Serve(clientRequests, quit, done)
clientRequests <- &Request{4}
clientRequests <- &Request{1}
clientRequests <- &Request{2}
clientRequests <- &Request{3}
clientRequests <- &Request{5}
clientRequests <- &Request{6}
clientRequests <- &Request{7}
clientRequests <- &Request{8}
clientRequests <- &Request{9}
fmt.Println( "...........>", <- done )
close(clientRequests)
close(done)
}
On execution I get the following error. I don't see whats wrong with the implementation, I am even closing the channel.
4 --- &{4}
0 --- &{1}
1 --- &{2}
2 --- &{3}
3 --- &{5}
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [chan send]:
main.main()
/home/ubuntu/digs-svc/src/digs/go1.go:45 +0x251
goroutine 5 [chan receive]:
main.Serve(0xc82004c060, 0xc82004c0c0, 0xc82004c120)
/home/ubuntu/digs-svc/src/digs/go1.go:28 +0x92
created by main.main
/home/ubuntu/digs-svc/src/digs/go1.go:37 +0xb9
goroutine 6 [chan send]:
main.handle(0xc82004c060, 0x0, 0xc82004c120)
/home/ubuntu/digs-svc/src/digs/go1.go:16 +0x23b
created by main.Serve
/home/ubuntu/digs-svc/src/digs/go1.go:25 +0x5b
EDIT:
Apparently, the fmt.Println("....", <- done)
wasn't enough to signify that there is a consumer to the done
channel. I moved the code up in the execution order. A consumer needs to be "listening" on the channel when data is written to it. In my earlier code, the when the first data was written there were no consumer.
Working code.