序
本文主要研究一下klog的Flush
Flush
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// Flush flushes all pending log I/O.
func Flush() {
logging.lockAndFlushAll()
}
Flush方法执行的是logging.lockAndFlushAll()
init
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// init sets up the defaults and runs flushDaemon.
func init() {
logging.stderrThreshold = errorLog // Default stderrThreshold is ERROR.
logging.setVState(0, nil, false)
logging.logDir = ""
logging.logFile = ""
logging.logFileMaxSizeMB = 1800
logging.toStderr = true
logging.alsoToStderr = false
logging.skipHeaders = false
logging.addDirHeader = false
logging.skipLogHeaders = false
logging.oneOutput = false
go logging.flushDaemon()
}
klog的init方法异步协程执行logging.flushDaemon()
logging.flushDaemon()
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// flushDaemon periodically flushes the log file buffers.
func (l *loggingT) flushDaemon() {
for range time.NewTicker(flushInterval).C {
l.lockAndFlushAll()
}
}
flushDaemon方法range新建ticker的channel，然后执行l.lockAndFlushAll()
lockAndFlushAll
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// lockAndFlushAll is like flushAll but locks l.mu first.
func (l *loggingT) lockAndFlushAll() {
l.mu.Lock()
l.flushAll()
l.mu.Unlock()
}
lockAndFlushAll使用lock执行flushAll
flushAll
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制const (
infoLog severity = iota
warningLog
errorLog
fatalLog
numSeverity = 4
)
// flushAll flushes all the logs and attempts to "sync" their data to disk.
// l.mu is held.
func (l *loggingT) flushAll() {
// Flush from fatal down, in case there's trouble flushing.
for s := fatalLog; s >= infoLog; s-- {
file := l.file[s]
if file != nil {
file.Flush() // ignore error
file.Sync() // ignore error
}
}
}
flushAll方法从fatalLog开始递减到infoLog级别挨个执行l.file[s]的Flush及Sync方法
flushSyncWriter
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// flushSyncWriter is the interface satisfied by logging destinations.
type flushSyncWriter interface {
Flush() error
Sync() error
io.Writer
}
type Writer interface {
Write(p []byte) (n int, err error)
}
flushSyncWriter接口定义了Flush、Sync方法，内嵌了io.Writer接口
redirectBuffer
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// redirectBuffer is used to set an alternate destination for the logs
type redirectBuffer struct {
w io.Writer
}
func (rb *redirectBuffer) Sync() error {
return nil
}
func (rb *redirectBuffer) Flush() error {
return nil
}
func (rb *redirectBuffer) Write(bytes []byte) (n int, err error) {
return rb.w.Write(bytes)
}
redirectBuffer内嵌了io.Writer，其Write方法通过io.Writer来写；其Sync及Flush方法都为空操作
syncBuffer
k8s.io/klog/v2@v2.4.0/klog.go
代码语言：javascript复制// syncBuffer joins a bufio.Writer to its underlying file, providing access to the
// file's Sync method and providing a wrapper for the Write method that provides log
// file rotation. There are conflicting methods, so the file cannot be embedded.
// l.mu is held for all its methods.
type syncBuffer struct {
logger *loggingT
*bufio.Writer
file *os.File
sev severity
nbytes uint64 // The number of bytes written to this file
maxbytes uint64 // The max number of bytes this syncBuffer.file can hold before cleaning up.
}
func (sb *syncBuffer) Sync() error {
return sb.file.Sync()
}
func (sb *syncBuffer) Write(p []byte) (n int, err error) {
if sb.nbytes uint64(len(p)) >= sb.maxbytes {
if err := sb.rotateFile(time.Now(), false); err != nil {
sb.logger.exit(err)
}
}
n, err = sb.Writer.Write(p)
sb.nbytes = uint64(n)
if err != nil {
sb.logger.exit(err)
}
return
}
syncBuffer定义了logger、file、sev、nbytes、maxbytes属性，内嵌了
*bufio.Writer；其Sync方法执行的是*os.File.Sync；其Flush方法执行的是*bufio.Writer.Flush
Flush
/usr/local/go/src/bufio/bufio.go
代码语言：javascript复制type Writer struct {
err error
buf []byte
n int
wr io.Writer
}
// Flush writes any buffered data to the underlying io.Writer.
func (b *Writer) Flush() error {
if b.err != nil {
return b.err
}
if b.n == 0 {
return nil
}
n, err := b.wr.Write(b.buf[0:b.n])
if n < b.n && err == nil {
err = io.ErrShortWrite
}
if err != nil {
if n > 0 && n < b.n {
copy(b.buf[0:b.n-n], b.buf[n:b.n])
}
b.n -= n
b.err = err
return err
}
b.n = 0
return nil
}
*bufio.Writer.Flush方法执行的是底层io.Writer的Write方法
rotateFile
代码语言：javascript复制// rotateFile closes the syncBuffer's file and starts a new one.
// The startup argument indicates whether this is the initial startup of klog.
// If startup is true, existing files are opened for appending instead of truncated.
func (sb *syncBuffer) rotateFile(now time.Time, startup bool) error {
if sb.file != nil {
sb.Flush()
sb.file.Close()
}
var err error
sb.file, _, err = create(severityName[sb.sev], now, startup)
if err != nil {
return err
}
if startup {
fileInfo, err := sb.file.Stat()
if err != nil {
return fmt.Errorf("file stat could not get fileinfo: %v", err)
}
// init file size
sb.nbytes = uint64(fileInfo.Size())
} else {
sb.nbytes = 0
}
sb.Writer = bufio.NewWriterSize(sb.file, bufferSize)
if sb.logger.skipLogHeaders {
return nil
}
// Write header.
var buf bytes.Buffer
fmt.Fprintf(&buf, "Log file created at: %sn", now.Format("2006/01/02 15:04:05"))
fmt.Fprintf(&buf, "Running on machine: %sn", host)
fmt.Fprintf(&buf, "Binary: Built with %s %s for %s/%sn", runtime.Compiler, runtime.Version(), runtime.GOOS, runtime.GOARCH)
fmt.Fprintf(&buf, "Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msgn")
n, err := sb.file.Write(buf.Bytes())
sb.nbytes = uint64(n)
return err
}
syncBuffer.rotateFile方法会设置其Writer为bufio.NewWriterSize(sb.file, bufferSize)，底层writer为syncBuffer的file
小结
klog的init方法异步协程执行logging.flushDaemon()，它内部执行的是l.lockAndFlushAll()；Flush方法是执行l.lockAndFlushAll()；l.lockAndFlushAll()方法使用lock执行flushAll；flushAll方法从fatalLog开始递减到infoLog级别挨个执行l.file[s]的Flush及Sync方法；对于redirectBuffer，其Flush及Sync方法为空操作；对于syncBuffer，其Sync方法执行的是*os.File.Sync；其Flush方法执行的是*bufio.Writer.Flush，*bufio.Writer.Flush方法执行的是底层io.Writer的Write方法，即syncBuffer的file的Write方法。
doc
- klog
