glog: update glog to the latest internal version (#59)

This change upstreams a number of changes since the last package update.

In particular this adds:

- New exported APIs (see godoc for further details):
  - glog.VDepth
  - glog.InfoDepthf
  - glog.WarningDepthf
  - glog.ErrorDepthf
  - glog.FatalDepthf
  - glog.ExitDepthf
  - glog.Names
  - glog.NewStandardLogger
  - glog.Verbose.InfoDepth
  - glog.Verbose.InfoDepthf
  - glog.ErrNoLog

- The -log_backtrace_at flag accepts now a comma-separated list of file:line locations.

- The -vmodule flag accepts a new syntax to match the full path to a module instead of just the module name. See the updated package documentation.

- A new internal/logsink package to support other outputs than files. Note: This package is internal, because we cannot guarantee at this point that the API remains stable.

More details at go/log-vs-glog (google-internal).

Author: chressie

glog.go

@@ -0,0 +1,164 @@
+package glog
+
+import (
+	"flag"
+	"io/ioutil"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// discarder is a flushSyncWriter that discards all data.
+// Sync sleeps for 10ms to simulate a disk seek.
+type discarder struct {
+}
+
+func (d *discarder) Write(data []byte) (int, error) {
+	return len(data), nil
+}
+
+func (d *discarder) Flush() error {
+	return nil
+}
+
+func (d *discarder) Sync() error {
+	time.Sleep(10 * time.Millisecond)
+	return nil
+}
+
+func (d *discarder) filenames() []string {
+	return nil
+}
+
+// newDiscard sets the log writers to all new byte buffers and returns the old array.
+func (s *fileSink) newDiscarders() severityWriters {
+	return s.swap(severityWriters{new(discarder), new(discarder), new(discarder), new(discarder)})
+}
+
+func discardStderr() func() {
+	se := sinks.stderr.w
+	sinks.stderr.w = ioutil.Discard
+	return func() { sinks.stderr.w = se }
+}
+
+const message = "benchmark log message"
+
+func benchmarkLog(b *testing.B, log func(...any)) {
+	defer sinks.file.swap(sinks.file.newDiscarders())
+	defer discardStderr()()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		log(message)
+	}
+	b.StopTimer()
+}
+
+func benchmarkLogConcurrent(b *testing.B, log func(...any)) {
+	defer sinks.file.swap(sinks.file.newDiscarders())
+	defer discardStderr()()
+	b.ResetTimer()
+	concurrency := runtime.GOMAXPROCS(0)
+	var wg sync.WaitGroup
+	wg.Add(concurrency)
+	for i := 0; i < concurrency; i++ {
+		go func() {
+			for i := 0; i < b.N; i++ {
+				log(message)
+			}
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	b.StopTimer()
+}
+
+func BenchmarkInfo(b *testing.B) {
+	benchmarkLog(b, Info)
+}
+
+func BenchmarkInfoConcurrent(b *testing.B) {
+	benchmarkLogConcurrent(b, Info)
+}
+
+func BenchmarkWarning(b *testing.B) {
+	benchmarkLog(b, Warning)
+}
+
+func BenchmarkWarningConcurrent(b *testing.B) {
+	benchmarkLogConcurrent(b, Warning)
+}
+
+func BenchmarkError(b *testing.B) {
+	benchmarkLog(b, Error)
+}
+
+func BenchmarkErrorConcurrent(b *testing.B) {
+	benchmarkLogConcurrent(b, Error)
+}
+
+func mixer() func(...any) {
+	var i int64
+	return func(args ...any) {
+		n := atomic.AddInt64(&i, 1)
+		switch {
+		case n%10000 == 0:
+			Error(args...)
+		case n%1000 == 0:
+			Warning(args...)
+		default:
+			Info(args...)
+		}
+	}
+}
+
+func BenchmarkMix(b *testing.B) {
+	benchmarkLog(b, mixer())
+}
+
+func BenchmarkMixConcurrent(b *testing.B) {
+	benchmarkLogConcurrent(b, mixer())
+}
+
+func BenchmarkVLogDisabled(b *testing.B) {
+	benchmarkLog(b, vlog)
+}
+
+func BenchmarkVLogDisabledConcurrent(b *testing.B) {
+	benchmarkLogConcurrent(b, vlog)
+}
+
+func BenchmarkVLogModuleFlagSet(b *testing.B) {
+	defer withVmodule("nonexistant=5")()
+	benchmarkLog(b, vlog)
+}
+
+func BenchmarkVLogModuleFlagSetConcurrent(b *testing.B) {
+	defer withVmodule("nonexistant=5")()
+	benchmarkLogConcurrent(b, vlog)
+}
+
+func BenchmarkVLogEnabled(b *testing.B) {
+	defer withVmodule("glog_bench_test=5")()
+	if got := bool(V(3)); got != true {
+		b.Fatalf("V(3) == %v, want %v", got, true)
+	}
+	benchmarkLog(b, vlog)
+}
+
+func BenchmarkVLogEnabledConcurrent(b *testing.B) {
+	defer withVmodule("glog_bench_test=5")()
+	benchmarkLogConcurrent(b, vlog)
+}
+
+func vlog(args ...any) {
+	V(3).Info(args)
+}
+
+func withVmodule(val string) func() {
+	if err := flag.Set("vmodule", val); err != nil {
+		panic(err)
+	}
+	return func() { flag.Set("vmodule", "") }
+}