_content/blog/execution-traces-2024/flightrecorder.go

//go:build OMIT

package main

import (
	"bytes"
	"log"
	"net/http"
	"os"
	"sync"
	"time"

	"golang.org/x/exp/trace"
)

func main() {
	// START OMIT
	// Set up the flight recorder.
	fr := trace.NewFlightRecorder()
	fr.Start()

	// Set up and run an HTTP server.
	var once sync.Once
	http.HandleFunc("/my-endpoint", func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()

		// Do the work...
		doWork(w, r)

		// We saw a long request. Take a snapshot!
		if time.Since(start) > 300*time.Millisecond {
			// Do it only once for simplicitly, but you can take more than one.
			once.Do(func() {
				// Grab the snapshot.
				var b bytes.Buffer
				_, err = fr.WriteTo(&b)
				if err != nil {
					log.Print(err)
					return
				}
				// Write it to a file.
				if err := os.WriteFile("trace.out", b.Bytes(), 0o755); err != nil {
					log.Print(err)
					return
				}
			})
		}
	})
	log.Fatal(http.ListenAndServe(":8080", nil))
	// END OMIT
}

func doWork(_ http.ResponseWriter, _ *http.Request) {
}