fix: data race in Default and SetDefault

[op]

This adds synchronisation primitives around all uses of the defaultLogger.

atomic.Pointer was introduced in Go 1.19. I see you have 1.19 in .github/ and go.mod, but maybe you still try to be backwards compatible? If so, I can replace atomic.Pointer with atomic.Value.

UPDATE: I see now that in #111, on purpose we delay initialisation of the logger. Reading about init in Effective Go it looks like using func init() should work fine.

[..] init is called after all the variable declarations in the package have evaluated their initializers, and those are evaluated only after all the imported packages have been initialized.

(An alternative solution exists at e31f99c but is more complicated imho. Most likely the problem with escape sequence during initialisation was because of the race within this package.)

Fixes #121.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.03%. Comparing base (2338a13) to head (3e0b742).
Report is 15 commits behind head on main.

❗ Current head 3e0b742 differs from pull request most recent head e31f99c. Consider uploading reports for the commit e31f99c to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #122      +/-   ##
==========================================
+ Coverage   80.92%   81.03%   +0.11%     
==========================================
  Files          11       11              
  Lines         739      654      -85     
==========================================
- Hits          598      530      -68     
+ Misses        126      109      -17     
  Partials       15       15              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[aymanbagabas]

Thank you @op for the PR!

atomic.Pointer was introduced in Go 1.19. I see you have 1.19 in .github/ and go.mod, but maybe you still try to be backwards compatible? If so, I can replace atomic.Pointer with atomic.Value.

Go 1.19 looks good, this is the minimum Go requirement for this package.

UPDATE: I see now that in #111, on purpose we delay initialisation of the logger. Reading about init in Effective Go it looks like using func init() should work fine.

[..] init is called after all the variable declarations in the package have evaluated their initializers, and those are evaluated only after all the imported packages have been initialized.

(An alternative solution exists at e31f99c but is more complicated imho. Most likely the problem with escape sequence during initialisation was because of the race within this package.)

I'm leaning more towards the alternative solution since AFAICT, in some cases init() can get called before Default(). We want to delay the logger initialization till the first call to log.

[op]

@aymanbagabas Sounds fair! I've updated the PR to make sure that you're able to cal SetDefault to prevent any default initialisation taking place.