change the position of the lock

[pantianying]

What this PR does:

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-io]

Codecov Report

Merging #286 into develop will increase coverage by 0.3%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           develop     #286     +/-   ##
==========================================
+ Coverage    65.52%   65.82%   +0.3%     
==========================================
  Files          111      112      +1     
  Lines         7063     7175    +112     
==========================================
+ Hits          4628     4723     +95     
- Misses        1978     1990     +12     
- Partials       457      462      +5

Impacted Files	Coverage Δ
registry/protocol/protocol.go	81.73% <0%> (-1.83%)	⬇️
protocol/dubbo/pool.go	59.51% <100%> (+1.64%)	⬆️
config/service.go	92.3% <0%> (-7.7%)	⬇️
common/proxy/proxy.go	97.75% <0%> (-2.25%)	⬇️
registry/etcdv3/registry.go	50.5% <0%> (-1.02%)	⬇️
protocol/dubbo/codec.go	76.47% <0%> (ø)	⬆️
common/rpc_service.go	88.54% <0%> (ø)	⬆️
config/method_config.go	50% <0%> (ø)	⬆️
cluster/loadbalance/consistent_hash.go	91.17% <0%> (ø)
common/url.go	69.28% <0%> (+0.3%)	⬆️
... and 5 more

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[fangyincheng]

LGTM

[zouyx]

LGTM