make sure thread safe

[qicosmos]

Fix #132

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.75%. Comparing base (4fb707c) to head (9083a15).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #133      +/-   ##
==========================================
+ Coverage   54.29%   54.75%   +0.45%     
==========================================
  Files         170      164       -6     
  Lines        8039     7946      -93     
==========================================
- Hits         4365     4351      -14     
+ Misses       3674     3595      -79     

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[github-actions]

Code Coverage Report
for detail, goto summary download Artifacts

Filename                    Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
client_util.hpp                     4                 1    75.00%          25                10    60.00%           4                 2    50.00%
codec.h                             4                 0   100.00%          24                 2    91.67%           0                 0         -
connection.h                       40                 4    90.00%         380                93    75.53%          72                37    48.61%
io_service_pool.h                   5                 0   100.00%          32                 1    96.88%          12                 1    91.67%
md5.hpp                            19                 2    89.47%         127                 8    93.70%          24                 0   100.00%
router.h                           19                 2    89.47%         144                35    75.69%           4                 3    25.00%
rpc_client.hpp                     74                 6    91.89%         669               120    82.06%         132                56    57.58%
rpc_server.h                       28                 3    89.29%         205                20    90.24%          44                10    77.27%
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                             193                18    90.67%        1606               289    82.00%         292               109    62.67%