How was there a future John Connor to send Kyle Reese back in time if Kyle is his father?

I watched Terminator Salvation over the weekend and it got me thinking. I cannot seem to get my head around how, if Kyle Reese is John's father, there was a John Connor in the future (2029) to send Kyle Reese back in time to protect Sarah Connor in 1984. There would be no future John if Kyle had never gone back in time, so how could 2029 John send Kyle back to 1984 as Kyle had not gone back yet and impregnated Sarah? 2029 John Connor would never have existed to send Kyle back. Does that make sense?