len, cap of channel: 0 0
recv from open channel: 1 true
received num: 2
received num: 3
slept
received num: 4
received num: 5
received num: 6
received num: 7
received num: 8
recv from closed channel: 0 false
got n: 10
got n: 11
got n: 10
got n: 11
got n: 10
got n: 11
sum: 25
sum: 29
sum: 33
sum(100): 4950