log: avoid stack lookups when not needed/used

log/format.go

@@ -33,8 +33,16 @@ var locationTrims = []string{
 // format output.
 func PrintOrigins(print bool) {
 	locationEnabled.Store(print)
+	if print {
+		stackEnabled.Store(true)
+	}
 }
 
+// storeStackRecords is an atomic flag controlling whether the log handler needs
+// to store the callsite stack. This is needed in case any handler wants to
+// print locations (locationEnabled), use vmodule, or print full stacks (BacktraceAt).
+var stackEnabled atomic.Bool
+
 // locationEnabled is an atomic flag controlling whether the terminal formatter
 // should append the log locations too when printing entries.
 var locationEnabled atomic.Bool

log/handler_glog.go

@@ -139,7 +139,10 @@ func (h *GlogHandler) Vmodule(ruleset string) error {
 	h.patterns = filter
 	h.siteCache = make(map[uintptr]Lvl)
 	h.override.Store(len(filter) != 0)
-
+	// Enable location storage (globally)
+	if len(h.patterns) > 0 {
+		stackEnabled.Store(true)
+	}
 	return nil
 }
 
@@ -172,7 +175,8 @@ func (h *GlogHandler) BacktraceAt(location string) error {
 
 	h.location = location
 	h.backtrace.Store(len(location) > 0)
-
+	// Enable location storage (globally)
+	stackEnabled.Store(true)
 	return nil
 }
 

log/logger.go

@@ -177,19 +177,22 @@ type logger struct {
 }
 
 func (l *logger) write(msg string, lvl Lvl, ctx []interface{}, skip int) {
-	l.h.Log(&Record{
+	record := &Record{
 		Time: time.Now(),
 		Lvl:  lvl,
 		Msg:  msg,
 		Ctx:  newContext(l.ctx, ctx),
-		Call: stack.Caller(skip),
 		KeyNames: RecordKeyNames{
 			Time: timeKey,
 			Msg:  msgKey,
 			Lvl:  lvlKey,
 			Ctx:  ctxKey,
 		},
-	})
+	}
+	if stackEnabled.Load() {
+		record.Call = stack.Caller(skip)
+	}
+	l.h.Log(record)
 }
 
 func (l *logger) New(ctx ...interface{}) Logger {

log/logger_test.go

@@ -0,0 +1,68 @@
+package log
+
+import (
+	"bytes"
+	"os"
+	"strings"
+	"testing"
+	"time"
+)
+
+func BenchmarkTraceLogging(b *testing.B) {
+	Root().SetHandler(LvlFilterHandler(LvlInfo, StreamHandler(os.Stderr, TerminalFormat(true))))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		Trace("a message", "v", i)
+	}
+}
+
+type notimeHandler struct {
+	next Handler
+}
+
+func (n notimeHandler) Log(r *Record) error {
+	r.Time = time.Unix(0, 0)
+	return n.next.Log(r)
+}
+
+// TestLoggingWithTrace checks that if BackTraceAt is set, then the
+// gloghandler is capable of spitting out a stacktrace
+func TestLoggingWithTrace(t *testing.T) {
+	defer stackEnabled.Store(stackEnabled.Load())
+	out := new(bytes.Buffer)
+	logger := New()
+	{
+		glog := NewGlogHandler(StreamHandler(out, TerminalFormat(false)))
+		glog.Verbosity(LvlTrace)
+		if err := glog.BacktraceAt("logger_test.go:42"); err != nil {
+			t.Fatal(err)
+		}
+		logger.SetHandler(notimeHandler{glog})
+	}
+	logger.Trace("a message", "foo", "bar") // Will be bumped to INFO
+	have := out.String()
+	wantPrefix := "INFO [01-01|01:00:00.000] a message\n\ngoroutine"
+	if len(have) < len(wantPrefix) || !strings.HasPrefix(have, wantPrefix) {
+		t.Errorf("\nhave: %q\nwant: %q\n", have, wantPrefix)
+	}
+}
+
+// TestLoggingWithVmodule checks that vmodule works.
+func TestLoggingWithVmodule(t *testing.T) {
+	defer stackEnabled.Store(stackEnabled.Load())
+	out := new(bytes.Buffer)
+	logger := New()
+	{
+		glog := NewGlogHandler(StreamHandler(out, TerminalFormat(false)))
+		glog.Verbosity(LvlCrit)
+		logger.SetHandler(notimeHandler{glog})
+		logger.Warn("This should not be seen", "ignored", "true")
+		glog.Vmodule("logger_test.go=5")
+	}
+	logger.Trace("a message", "foo", "bar")
+	have := out.String()
+	want := "TRACE[01-01|01:00:00.000] a message                                foo=bar\n"
+	if have != want {
+		t.Errorf("\nhave: %q\nwant: %q\n", have, want)
+	}
+}