[Insei]

The logger is often configured by the config, but the config is parsed by the manager that already needs the logger. WithDeferredLogger keeps the log records in memory, and Manager.SetLogger writes them to the logger created from the parsed config.

config, _ := tinyconf.New(tinyconf.WithDriver(...), tinyconf.WithDeferredLogger())
err := config.Parse(ctx, conf)
config.SetLogger(newLogger(conf.Logging)) // the records of Parse are written to it
tinyconf.Subscribe(ctx, config, func(_, next *Logging) { config.SetLogger(newLogger(*next)) })

• SetLogger is safe for concurrent use: the logger is stored in atomic.Pointer, the kept records are written under the mutex, the records written concurrently wait for them, and the loggers taken before SetLogger (by Parse running at the same time) write to the current logger of the manager. Nothing is lost, the order is kept.
• Up to 1000 records are kept, the oldest are dropped with a warning about their count. SetLogger(nil) disables logging.
• Without WithDeferredLogger nothing is kept, SetLogger only replaces the logger; the behaviour of the existing code is not changed.
• ExampleWithDeferredLogger with slog (Go 1.21+), the example service creates its logger from the config and follows the changes of the level, checked by hand with the change of config.yaml.
• Race test of SetLogger with concurrent Parse and writers.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (335bb93) to head (6e74f4b).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #52   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           31        32    +1     
  Lines         2581      2630   +49     
=========================================
+ Hits          2581      2630   +49     

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[github-actions]

Benchmark diff: 335bb93 → 5680f8c (10 runs)

goos: linux
goarch: amd64
pkg: github.com/insei/tinyconf/v2
cpu: AMD EPYC 7763 64-Core Processor                
                    │  base.txt   │              head.txt              │
                    │   sec/op    │   sec/op     vs base               │
Parse-4               8.516µ ± 1%   8.518µ ± 1%       ~ (p=0.796 n=10)
Parse_SubConfig-4     3.008µ ± 0%   3.050µ ± 2%  +1.40% (p=0.000 n=10)
Current-4             55.16n ± 0%   55.33n ± 0%  +0.30% (p=0.024 n=10)
Current_SubConfig-4   98.02n ± 0%   98.81n ± 1%  +0.82% (p=0.000 n=10)
geomean               610.0n        613.9n       +0.64%

                    │    base.txt    │               head.txt                │
                    │      B/op      │     B/op      vs base                 │
Parse-4               4.899Ki ± 0%     4.899Ki ± 0%       ~ (p=1.000 n=10) ¹
Parse_SubConfig-4     1.367Ki ± 0%     1.367Ki ± 0%       ~ (p=1.000 n=10) ¹
Current-4               0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
Current_SubConfig-4     0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                            ²                 +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                    │   base.txt   │              head.txt               │
                    │  allocs/op   │ allocs/op   vs base                 │
Parse-4               139.0 ± 0%     139.0 ± 0%       ~ (p=1.000 n=10) ¹
Parse_SubConfig-4     44.00 ± 0%     44.00 ± 0%       ~ (p=1.000 n=10) ¹
Current-4             0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
Current_SubConfig-4   0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                          ²               +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

pkg: github.com/insei/tinyconf/v2/drivers
                │  base.txt   │           head.txt            │
                │   sec/op    │   sec/op     vs base          │
Parse_Drivers-4   75.05µ ± 1%   75.22µ ± 2%  ~ (p=0.739 n=10)

                │   base.txt   │            head.txt            │
                │     B/op     │     B/op      vs base          │
Parse_Drivers-4   32.04Ki ± 0%   32.04Ki ± 0%  ~ (p=1.000 n=10)

                │  base.txt  │            head.txt            │
                │ allocs/op  │ allocs/op   vs base            │
Parse_Drivers-4   645.0 ± 0%   645.0 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal