文件输出引擎使用到的读写锁 sync.RWMutex读写锁是一种同步机制，允许多个读操作同时读取数据，但是只允许一个写操作写数据。锁的状态有三种：读模式加锁、写模式加锁、无锁。无锁。读/写进程都可以进入。读模式锁。读进程可以进入。写进程不可以进入。写模式锁。读/写进程都不可以进入。就拿文件行数这个变量来看，如果开启了日志文件按小时按行数切割的功能，要先读取当前文件行数变量值。当并发情况下，多个 goroutine 在打日志，读取文件行数和修改文件行数便成为一对“读写”操作，所以需要用读写锁，读写锁对于读操作不会导致锁竞争和 goroutine 阻塞。// WriteMsg write logger message into file.func (w *fileLogWriter) WriteMsg(when time.Time, msg string, level int) error { ··· if w.Rotate { w.RLock() if w.needRotateHourly(len(msg), h) { w.RUnlock() w.Lock() if w.needRotateHourly(len(msg), h) { if err := w.doRotate(when); err != nil { fmt.Fprintf(os.Stderr, “FileLogWriter(%q): %s\n”, w.Filename, err) } } w.Unlock() } else if w.needRotateDaily(len(msg), d) { w.RUnlock() w.Lock() if w.needRotateDaily(len(msg), d) { if err := w.doRotate(when); err != nil { fmt.Fprintf(os.Stderr, “FileLogWriter(%q): %s\n”, w.Filename, err) } } w.Unlock() } else { w.RUnlock() } } w.Lock() , err := w.fileWriter.Write([]byte(msg)) if err == nil { w.maxLinesCurLines++ w.maxSizeCurSize += len(msg) } w.Unlock() ···}总结下 Goroutine 的使用监听 msgChan第一处是开启异步选项时，启动一个 goroutine 监听 msgChan 是否为空，发现不为空便取走日志信息进行输出。// Async set the log to asynchronous and start the goroutinefunc (bl *BeeLogger) Async(msgLen …int64) *BeeLogger { ··· go bl.startLogger() ···}// start logger chan reading.// when chan is not empty, write logs.func (bl *BeeLogger) startLogger() { gameOver := false for { select { case bm := <-bl.msgChan: bl.writeToLoggers(bm.when, bm.msg, bm.level) logMsgPool.Put(bm) ··· } ··· }}监听计时器实现日志文件按日期分割文件输出引擎 file.go 文件中，初始化 fileWriter *os.File 时启动一个 goroutine 执行 dailyRotate() ：func (w *fileLogWriter) initFd() error { fd := w.fileWriter fInfo, err := fd.Stat() if err != nil { return fmt.Errorf(“get stat err: %s”, err) } w.maxSizeCurSize = int(fInfo.Size()) w.dailyOpenTime = time.Now() w.dailyOpenDate = w.dailyOpenTime.Day() w.maxLinesCurLines = 0 if w.Daily { go w.dailyRotate(w.dailyOpenTime) // <—— } if fInfo.Size() > 0 && w.MaxLines > 0 { count, err := w.lines() if err != nil { return err } w.maxLinesCurLines = count } return nil}dailyRotate() 方法中，tm 定时器时间一到，便会往 tm.C 通道发送当前时间，此时 a 语句便停止阻塞，可以继续往下执行。func (w *fileLogWriter) dailyRotate(openTime time.Time) { y, m, d := openTime.Add(24 * time.Hour).Date() nextDay := time.Date(y, m, d, 0, 0, 0, 0, openTime.Location()) tm := time.NewTimer(time.Duration(nextDay.UnixNano() - openTime.UnixNano() + 100)) <-tm.C // <— a 语句 w.Lock() if w.needRotate(0, time.Now().Day()) { if err := w.doRotate(time.Now()); err != nil { fmt.Fprintf(os.Stderr, “FileLogWriter(%q): %s\n”, w.Filename, err) } } w.Unlock()}开启新的 goroutine 删除失效的日志文件因为删除文件涉及文件 IO 处理，为了避免阻塞主线程，便交由另外 goroutine 去做。，go w.deleteOldLog()，超过 MaxDays 的日志文件便是失效的。// DoRotate means it need to write file in new file.// new file name like xx.2013-01-01.log (daily) or xx.001.log (by line or size)func (w fileLogWriter) doRotate(logTime time.Time) error { ··· err = os.Rename(w.Filename, fName) ··· startLoggerErr := w.startLogger() go w.deleteOldLog() ···}func (w fileLogWriter) deleteOldLog() { dir := filepath.Dir(w.Filename) filepath.Walk(dir, func(path string, info os.FileInfo, err error) (returnErr error) { defer func() { if r := recover(); r != nil { fmt.Fprintf(os.Stderr, “Unable to delete old log ‘%s’, error: %v\n”, path, r) } }() if info == nil { return } if !info.IsDir() && info.ModTime().Add(24time.Hourtime.Duration(w.MaxDays)).Before(time.Now()) { if strings.HasPrefix(filepath.Base(path), filepath.Base(w.fileNameOnly)) && strings.HasSuffix(filepath.Base(path), w.suffix) { os.Remove(path) } } return })}使用 goto 语句保证即使发生错误也要重启 LoggerdoRotate() 方法大体逻辑：重命名之前写入的日志文件，err = os.Rename(w.Filename, fName)首先找到 一个可用的 filename ，循环遍历1-999，如果找不到报错；,err:=os.Lstat(fName) ：若以 fName 为名的文件不存在则返回 err 不为空。os.Chmod(fName, os.FileMode(rotatePerm)) 修改文件权限。重新启动 Logger ：一是启动 Logger ，w.startLogger()；二是开启一个 goroutine 删除失效的日志文件。注意到下面代码段中的 a 语句和 b 语句，它们并不是返回错误阻止代码继续执行，而是即使发生错误也会保证重启一个新的 Logger。如果是执行到 a 语句这种情况，有可能是该日志文件已经被别的程序删除或者其他原因导致文件不存在，但大可不必因为一个日志文件的丢失而阻止了新 Logger 的启动，简而言之，这个错误是可以忽略的。// DoRotate means it need to write file in new file.// new file name like xx.2013-01-01.log (daily) or xx.001.log (by line or size)func (w *fileLogWriter) doRotate(logTime time.Time) error { // file exists // Find the next available number num := 1 fName := "" rotatePerm, err := strconv.ParseInt(w.RotatePerm, 8, 64) if err != nil { return err } _, err = os.Lstat(w.Filename) if err != nil { //even if the file is not exist or other ,we should RESTART the logger goto RESTART_LOGGER // <——- a 语句 } if w.MaxLines > 0 || w.MaxSize > 0 { for ; err == nil && num <= 999; num++ { fName = w.fileNameOnly + fmt.Sprintf(".%s.%03d%s", logTime.Format(“2006-01-02”), num, w.suffix) _, err = os.Lstat(fName) } } else { fName = fmt.Sprintf("%s.%s%s", w.fileNameOnly, w.dailyOpenTime.Format(“2006-01-02”), w.suffix) _, err = os.Lstat(fName) for ; err == nil && num <= 999; num++ { fName = w.fileNameOnly + fmt.Sprintf(".%s.%03d%s", w.dailyOpenTime.Format(“2006-01-02”), num, w.suffix) _, err = os.Lstat(fName) } } // return error if the last file checked still existed if err == nil { return fmt.Errorf( “Rotate: Cannot find free log number to rename %s”, w.Filename) } // close fileWriter before rename w.fileWriter.Close() // Rename the file to its new found name // even if occurs error,we MUST guarantee to restart new logger err = os.Rename(w.Filename, fName) if err != nil { goto RESTART_LOGGER // <——- b 语句 } err = os.Chmod(fName, os.FileMode(rotatePerm))RESTART_LOGGER: // <——- startLoggerErr := w.startLogger() go w.deleteOldLog() if startLoggerErr != nil { return fmt.Errorf(“Rotate StartLogger: %s”, startLoggerErr) } if err != nil { return fmt.Errorf(“Rotate: %s”, err) } return nil}涉及到 sync.WaitGroup 的使用a 语句处，开启 goroutine 前计数器加一，执行完该 goroutine 后计数器减一，即 b 语句。// Async set the log to asynchronous and start the goroutinefunc (bl *BeeLogger) Async(msgLen …int64) *BeeLogger { ··· bl.wg.Add(1) // <—– a 语句 go bl.startLogger() return bl}// start logger chan reading.// when chan is not empty, write logs.func (bl *BeeLogger) startLogger() { gameOver := false for { select { case bm := <-bl.msgChan: bl.writeToLoggers(bm.when, bm.msg, bm.level) logMsgPool.Put(bm) case sg := <-bl.signalChan: // Now should only send “flush” or “close” to bl.signalChan bl.flush() if sg == “close” { for _, l := range bl.outputs { l.Destroy() } bl.outputs = nil gameOver = true } bl.wg.Done() // <—— b 语句 } if gameOver { break } }}分析并发执行下面 Flush() 方法的情况。假设有 A , B , C 三个 goroutine,并且假设 A 先执行到 e 语句，从a 语句知道初始计数器为 1 ，所以 e 语句必须等到上述 startLogger-goroutine 执行 b 语句完毕后才停止阻塞。而后 A 再让计数器加一。因为 bl.signalChan 的缓存大小为1，所以 B,C 阻塞在 d 语句，等到 B,C 其中之一能执行 e 语句的时候计数器必然大于0，才不会导致永久阻塞。所以 f 语句要放在 e 语句之后。// Flush flush all chan data.func (bl *BeeLogger) Flush() { if bl.asynchronous { bl.signalChan <- “flush” // <—— d 语句 bl.wg.Wait() // <—— e 语句 bl.wg.Add(1) // <—— f 语句 return } bl.flush()}因此再看下面的 Close() 方法，它是不能并发执行的，会导致 “panic: close of closed channel"错误。不过笔者暂时没懂为什么 beego logs 不把这里做一下改进，让 Close() 也支持并发调用不好吗？// Close close logger, flush all chan data and destroy all adapters in BeeLogger.func (bl *BeeLogger) Close() { if bl.asynchronous { bl.signalChan <- “close” bl.wg.Wait() // <—— g 语句 close(bl.msgChan) } else { bl.flush() for _, l := range bl.outputs { l.Destroy() } bl.outputs = nil } close(bl.signalChan)}
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