From 9ad8250a786bfe8814e3372da089f70213742386 Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sun, 26 Jul 2020 18:54:41 +0200
Subject: [PATCH] Reduce overhead of debug calls if no log is enabled

In case no debug log is configured, then calls to debug.Log only incur
the costs to check a single boolean flag making the call really cheap.
---
 internal/debug/debug.go | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/internal/debug/debug.go b/internal/debug/debug.go
index 543755e25..3df2c2ef4 100644
--- a/internal/debug/debug.go
+++ b/internal/debug/debug.go
@@ -17,9 +17,10 @@ import (
 )
 
 var opts struct {
-	logger *log.Logger
-	funcs  map[string]bool
-	files  map[string]bool
+	isEnabled bool
+	logger    *log.Logger
+	funcs     map[string]bool
+	files     map[string]bool
 }
 
 // make sure that all the initialization happens before the init() functions
@@ -30,6 +31,12 @@ func initDebug() bool {
 	initDebugLogger()
 	initDebugTags()
 
+	if opts.logger == nil && len(opts.funcs) == 0 && len(opts.files) == 0 {
+		opts.isEnabled = false
+		return false
+	}
+
+	opts.isEnabled = true
 	fmt.Fprintf(os.Stderr, "debug enabled\n")
 
 	return true
@@ -173,6 +180,10 @@ func checkFilter(filter map[string]bool, key string) bool {
 
 // Log prints a message to the debug log (if debug is enabled).
 func Log(f string, args ...interface{}) {
+	if !opts.isEnabled {
+		return
+	}
+
 	fn, dir, file, line := getPosition()
 	goroutine := goroutineNum()