opt: reduce duplicate code for I/O reactors

[panjf2000]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.50%. Comparing base (5cca785) to head (a5bc95b).

Files	Patch %	Lines
reactor_default.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #590      +/-   ##
==========================================
- Coverage   79.76%   79.50%   -0.26%     
==========================================
  Files          23       21       -2     
  Lines        2184     2098      -86     
==========================================
- Hits         1742     1668      -74     
+ Misses        302      296       -6     
+ Partials      140      134       -6     

Flag	Coverage Δ
unittests	79.50% <50.00%> (-0.26%)	⬇️

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