Add -profile flag for CPU profiling (#2715)

There is already a commented-out code in main() for enabling CPU
profiling of micro, which is often useful. Adjust it to allow enabling
it just by providing -profile flag on the command line, without
modifying and recompiling the code.

cmd/micro/micro.go

@@ -9,6 +9,7 @@ import (
 	"os/signal"
 	"regexp"
 	"runtime"
+	"runtime/pprof"
 	"sort"
 	"strconv"
 	"syscall"
@@ -37,6 +38,7 @@ var (
 	flagConfigDir = flag.String("config-dir", "", "Specify a custom location for the configuration directory")
 	flagOptions   = flag.Bool("options", false, "Show all option help")
 	flagDebug     = flag.Bool("debug", false, "Enable debug mode (prints debug info to ./log.txt)")
+	flagProfile   = flag.Bool("profile", false, "Enable CPU profiling (writes profile info to ./micro.prof)")
 	flagPlugin    = flag.String("plugin", "", "Plugin command")
 	flagClean     = flag.Bool("clean", false, "Clean configuration directory")
 	optionFlags   map[string]*string
@@ -59,6 +61,9 @@ func InitFlags() {
 		fmt.Println("    \tShow all option help")
 		fmt.Println("-debug")
 		fmt.Println("    \tEnable debug mode (enables logging to ./log.txt)")
+		fmt.Println("-profile")
+		fmt.Println("    \tEnable CPU profiling (writes profile info to ./micro.prof")
+		fmt.Println("    \tso it can be analyzed later with \"go tool pprof micro.prof\")")
 		fmt.Println("-version")
 		fmt.Println("    \tShow the version number and information")
 
@@ -228,15 +233,21 @@ func main() {
 		os.Exit(0)
 	}()
 
-	// runtime.SetCPUProfileRate(400)
-	// f, _ := os.Create("micro.prof")
-	// pprof.StartCPUProfile(f)
-	// defer pprof.StopCPUProfile()
-
 	var err error
 
 	InitFlags()
 
+	if *flagProfile {
+		f, err := os.Create("micro.prof")
+		if err != nil {
+			log.Fatal("error creating CPU profile: ", err)
+		}
+		if err := pprof.StartCPUProfile(f); err != nil {
+			log.Fatal("error starting CPU profile: ", err)
+		}
+		defer pprof.StopCPUProfile()
+	}
+
 	InitLog()
 
 	err = config.InitConfigDir(*flagConfigDir)