Fix issue 3988

[huanghantao]

fix issue #3988

[codecov]

Codecov Report

Merging #3990 (cc4e36e) into master (d54258b) will increase coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3990      +/-   ##
==========================================
+ Coverage   48.92%   49.06%   +0.14%     
==========================================
  Files          69       69              
  Lines       12971    13003      +32     
==========================================
+ Hits         6346     6380      +34     
+ Misses       6625     6623       -2     

Impacted Files	Coverage Δ
src/os/async_thread.cc	68.99% <0.00%> (-0.44%)	⬇️
src/server/port.cc	54.07% <0.00%> (+0.32%)	⬆️
src/memory/buffer.cc	92.52% <0.00%> (+1.85%)	⬆️
src/protocol/base.cc	66.66% <0.00%> (+2.04%)	⬆️

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