fix deadlock among tasks

[zhenghaoz]

No description provided.

[codecov]

Codecov Report

Merging #554 (746ad12) into master (92e2404) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

❗ Current head 746ad12 differs from pull request most recent head 35ccb8d. Consider uploading reports for the commit 35ccb8d to get more accurate results

@@            Coverage Diff             @@
##           master     #554      +/-   ##
==========================================
- Coverage   71.21%   71.19%   -0.02%     
==========================================
  Files          62       62              
  Lines       11765    11770       +5     
==========================================
+ Hits         8378     8380       +2     
- Misses       2585     2587       +2     
- Partials      802      803       +1     

Impacted Files	Coverage Δ
base/task/schedule.go	92.78% <40.00%> (-2.87%)	⬇️
master/tasks.go	61.34% <100.00%> (ø)

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