Fix the log duplication issue for --log-file

when we use a `log-file`, all the items in l.file array point to the
same file. we are currently using a switch statement with fallthrough
which ends up logging the same line multiple times. So check if we are
using a `log-file` and just write the data once.

Change-Id: I3396558f487daf9db2c5e21e29a7a6bee618d64a

klog.go

@@ -781,24 +781,38 @@ func (l *loggingT) output(s severity, buf *buffer, file string, line int, alsoTo
 		if alsoToStderr || l.alsoToStderr || s >= l.stderrThreshold.get() {
 			os.Stderr.Write(data)
 		}
-		if l.file[s] == nil {
-			if err := l.createFiles(s); err != nil {
-				os.Stderr.Write(data) // Make sure the message appears somewhere.
-				l.exit(err)
+
+		if logging.logFile != "" {
+			// Since we are using a single log file, all of the items in l.file array
+			// will point to the same file, so just use one of them to write data.
+			if l.file[infoLog] == nil {
+				if err := l.createFiles(infoLog); err != nil {
+					os.Stderr.Write(data) // Make sure the message appears somewhere.
+					l.exit(err)
+				}
 			}
-		}
-		switch s {
-		case fatalLog:
-			l.file[fatalLog].Write(data)
-			fallthrough
-		case errorLog:
-			l.file[errorLog].Write(data)
-			fallthrough
-		case warningLog:
-			l.file[warningLog].Write(data)
-			fallthrough
-		case infoLog:
 			l.file[infoLog].Write(data)
+		} else {
+			if l.file[s] == nil {
+				if err := l.createFiles(s); err != nil {
+					os.Stderr.Write(data) // Make sure the message appears somewhere.
+					l.exit(err)
+				}
+			}
+
+			switch s {
+			case fatalLog:
+				l.file[fatalLog].Write(data)
+				fallthrough
+			case errorLog:
+				l.file[errorLog].Write(data)
+				fallthrough
+			case warningLog:
+				l.file[warningLog].Write(data)
+				fallthrough
+			case infoLog:
+				l.file[infoLog].Write(data)
+			}
 		}
 	}
 	if s == fatalLog {

klog_test.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	stdLog "log"
+	"os"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -521,6 +522,31 @@ func BenchmarkHeaderWithDir(b *testing.B) {
 	}
 }
 
+func BenchmarkLogs(b *testing.B) {
+	setFlags()
+	defer logging.swap(logging.newBuffers())
+
+	testFile, err := ioutil.TempFile("", "test.log")
+	if err != nil {
+		b.Error("unable to create temporary file")
+	}
+	defer os.Remove(testFile.Name())
+
+	logging.verbosity.Set("0")
+	logging.toStderr = false
+	logging.alsoToStderr = false
+	logging.stderrThreshold = fatalLog
+	logging.logFile = testFile.Name()
+	logging.swap([numSeverity]flushSyncWriter{nil, nil, nil, nil})
+
+	for i := 0; i < b.N; i++ {
+		Error("error")
+		Warning("warning")
+		Info("info")
+	}
+	logging.flushAll()
+}
+
 // Test the logic on checking log size limitation.
 func TestFileSizeCheck(t *testing.T) {
 	setFlags()