example_logger_test.go

package gctx_test

import (
	"context"
	"fmt"
	"sync"

	"github.com/ansiwen/gctx"
)

type requestID struct{}

// "global" logger instance
func log(s string) {
	ctx := gctx.Get()
	reqID, _ := ctx.Value(requestID{}).(int)
	fmt.Printf("[LOG] reqID: %d - %s\n", reqID, s)
}

// placeholder for an external library function without context support
// doing something and using a global logger
func someLibraryFunction() {
	/* ... */
	log("did something")
	/* ... */
}

func Example_logger() {
	var wg sync.WaitGroup
	// asynchronously call a library function for 5 times
	for i := 0; i < 5; i++ {
		wg.Add(1)
		ctx := context.WithValue(context.Background(), requestID{}, i)
		go func() {
			gctx.Set(ctx)
			someLibraryFunction()
			wg.Done()
		}()
	}
	wg.Wait()

	// Unordered output:
	// [LOG] reqID: 0 - did something
	// [LOG] reqID: 1 - did something
	// [LOG] reqID: 2 - did something
	// [LOG] reqID: 3 - did something
	// [LOG] reqID: 4 - did something
}