Go slog level switch demo

main.go

package main

import (
	"log/slog"
	"os"
	"os/signal"
	"syscall"
	"time"
)

var LOG_LEVEL = new(slog.LevelVar)

func main() {
	LOG_LEVEL.Set(slog.LevelInfo)

	opts := &slog.HandlerOptions{
		Level: LOG_LEVEL,
	}

	logger := slog.New(
		slog.NewTextHandler(os.Stdout, opts),
	)

	// trap SIGQUIT to toggle debug level
  // run in your terminal:
  //    kill -3 <pid>
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGQUIT)

	go func() {
		for {
			<-sigChan
			currentLevel := LOG_LEVEL.Level()
			if currentLevel != slog.LevelDebug {
				SetLogLevel(slog.LevelDebug)
			} else {
				SetLogLevel(slog.LevelInfo)
			}
			logger.Info("Log level changed")
		}
	}()

	counter := 0

	logger = logger.With("pid", os.Getpid())

	for {
		logger.Debug("ready to increase counter in 1s")
		time.Sleep(time.Second)
		counter++
		logger.Info("counter increased", "counter", counter)
		logger.Debug("cooldown for 1s")
		time.Sleep(time.Second)
	}
}

func SetLogLevel(lvl slog.Level) {
	LOG_LEVEL.Set(lvl)
}

Do note the default interpretation of SIGQUIT in Go that you're currently overriding:

The SIGQUIT signal is sent when the user at the controlling terminal presses the quit character, which by default is ^\ (Control-Backslash). In general you can cause a program to simply exit by pressing ^C, and you can cause it to exit with a stack dump by pressing ^\ .

Perhaps a better signal for runtime changing of log levels could be SIGUSR1 or SIGUSR2 (although I've seen many examples of SIGHUP being used for hot-reloading configuration as well).

Do note the default interpretation of SIGQUIT in Go that you're currently overriding:

The SIGQUIT signal is sent when the user at the controlling terminal presses the quit character, which by default is ^\ (Control-Backslash). In general you can cause a program to simply exit by pressing ^C, and you can cause it to exit with a stack dump by pressing ^\ .

Perhaps a better signal for runtime changing of log levels could be SIGUSR1 or SIGUSR2 (although I've seen many examples of SIGHUP being used for hot-reloading configuration as well).

yes i understand
its a trade-off after all

but still a good idea handle hot reload