The output of the sender has error
The output of the sender has error

when  if (dots.incrementAndGet() == 3)  dots.set(1), the value is 1,not 3,
so for (int i = 0; i < dots.get(); i++) { builder.append('.'); } can not println hello...   
it reality println
 [x] Sent 'Hello.1'
 [x] Sent 'Hello..2'
 [x] Sent 'Hello.3'
 [x] Sent 'Hello..4'
 ......
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