Add mutex and block profiling via envvar

cmd/prometheus/main.go

@@ -22,6 +22,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"syscall"
 	"time"
@@ -64,6 +65,11 @@ func init() {
 }
 
 func main() {
+	if os.Getenv("DEBUG") != "" {
+		runtime.SetBlockProfileRate(20)
+		runtime.SetMutexProfileFraction(20)
+	}
+
 	cfg := struct {
 		printVersion bool
 		configFile   string