Use time.Timer instead of time.After in either-or cases to avoid memory leak

[arijitAD]

Issue summary

The docs for time.After says

After waits for the duration to elapse and then sends the current time on the returned channel. It is equivalent to NewTimer(d).C. The underlying Timer is not recovered by the garbage collector until the timer fires. If efficiency is a concern, use NewTimer instead and call Timer.Stop if the timer is no longer needed.

We should replace time.After with time.Timer if we want to poll some code to avoid unnecessary allocation and deallocation.

Benchmark to compare time.After vs time.Sleep vs time.Timer vs time.Ticker

BenchmarkSleep-16    	   40676	     32230 ns/op	       0 B/op	       0 allocs/op
BenchmarkAfter-16    	   10000	    114656 ns/op	  200001 B/op	    3000 allocs/op
BenchmarkReset-16    	   27517	     44791 ns/op	     200 B/op	       3 allocs/op
BenchmarkTicker-16    	   31257	     35621 ns/op	     200 B/op	       3 allocs/op

https://play.golang.org/p/jfmFQQQv-0I

Other information and links

• https://golang.org/src/time/sleep.go?s=5504:5538#L150