use channels instead of atomics in update loop

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #763 into master will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #763      +/-   ##
==========================================
- Coverage   50.35%   50.33%   -0.03%     
==========================================
  Files         409      409              
  Lines       52949    52938      -11     
==========================================
- Hits        26663    26646      -17     
- Misses      24267    24276       +9     
+ Partials     2019     2016       -3     

Impacted Files	Coverage Δ
miner/miner.go	0.00% <0.00%> (ø)
miner/worker.go	0.00% <0.00%> (ø)
consensus/cuckoo/sealer.go	0.00% <0.00%> (-6.76%)	⬇️
consensus/cuckoo/cuckoo.go	31.57% <0.00%> (-4.22%)	⬇️
p2p/discover/table.go	84.19% <0.00%> (-2.44%)	⬇️
trie/proof.go	75.37% <0.00%> (-1.87%)	⬇️
p2p/simulations/mocker.go	35.45% <0.00%> (-1.82%)	⬇️
ctxc/downloader/statesync.go	57.89% <0.00%> (-1.06%)	⬇️
p2p/message.go	53.96% <0.00%> (-0.80%)	⬇️
p2p/server.go	66.60% <0.00%> (-0.39%)	⬇️
... and 6 more