config+lnd: add new option --cpuprofile for writing cpuprofile to file

In this commit we add a new option to lnd, cpuprofile. With this option
we add additional telemetry hooks into and, allowing users to generate
CPU profiling files to measure hot spots within the daemon.

lnd.go

@@ -16,6 +16,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"runtime"
+	"runtime/pprof"
 	"strconv"
 	"time"
 
@@ -88,6 +89,18 @@ func lndMain() error {
 		}()
 	}
 
+	// Write cpu profile if requested.
+	if cfg.CPUProfile != "" {
+		f, err := os.Create(cfg.CPUProfile)
+		if err != nil {
+			ltndLog.Errorf("Unable to create cpu profile: %v", err)
+			return err
+		}
+		pprof.StartCPUProfile(f)
+		defer f.Close()
+		defer pprof.StopCPUProfile()
+	}
+
 	// Open the channeldb, which is dedicated to storing channel, and
 	// network related metadata.
 	chanDB, err := channeldb.Open(cfg.DataDir)