GO语言实战十二 标准库 log
log 包学习和源码分析
测试代码
package main
import (
"fmt"
"log"
)
func init() {
log.SetPrefix("Trace: ")
log.SetFlags(log.Ldate | log.Lmicroseconds | log.Llongfile)
}
func main() {
// Println写到标准日志记录器
log.Println("我是日志啊---")
Fatalln 在调用 Println()之后会接着调用 os.Exit(1)
//log.Fatalln("出错了啊")
// Panicln 在调用 Println()之后会接着调用 panic()
log.Panicln("我是panic")
fmt.Println("end=========")
}
log源码分析
golang 源码直接查看即可，而且还有注释
使用翻译工具翻译下 哈哈
// Package log implements a simple logging package. It defines a type, Logger,
// with methods for formatting output. It also has a predefined 'standard'
// Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and
// Panic[f|ln], which are easier to use than creating a Logger manually.
// That logger writes to standard error and prints the date and time
// of each logged message.
// Every log message is output on a separate line: if the message being
// printed does not end in a newline, the logger will add one.
// The Fatal functions call os.Exit(1) after writing the log message.
// The Panic functions call panic after writing the log message.
package log
import (
"fmt"
"io"
"os"
"runtime"
"sync"
"time"
)
//这些标记定义了日志记录器生成的每个日志条目的前缀文本。
//将位元放在一起以控制打印的内容。
//它们出现的顺序(所列的顺序)是没有办法控制的
//这里)或它们呈现的格式(如注释中所述)。
//只有在Llongfile或Lshortfile时，前缀后面才跟一个冒号
// 例如 flags = Ldate | Ltime (or LstdFlags) 生成,
// 2009/01/23 01:23:23 message
// 例如 flags = Ldate | Ltime | Lmicroseconds | Llongfile 则生成,
// 2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message
const (
Ldate = 1 << iota // 1 日期: 2009/01/23
Ltime // 2 时间: 01:23:23
Lmicroseconds // 4 微秒
Llongfile // 8 完整的文件名和行号: /a/b/c/d.go:23
Lshortfile // 16 最后的文件名和行号:d.go:23。覆盖Llongfile
LUTC // 32 如果设置了Ldate或Ltime，请使用UTC而不是本地时区
LstdFlags = Ldate | Ltime // 3 默认值
)
//日志程序表示一个活动的日志对象，它生成的是
//输出给io.Writer。每个日志操作只调用一次
//作者的写作方法。一个记录器可以同时使用
// 多个了goroutine;它保证对写入器的序列化访问。
type Logger struct {
mu sync.Mutex // 确保原子写入;保护以下字段
prefix string // 每行的前缀字段
flag int // 属性字段 如log.Ldate|log.Ltime|log.Llongfile
out io.Writer // 输出目标
buf []byte // for accumulating text to write
}
//初始化对象，设置三个属性，输出、前缀、属性
func New(out io.Writer, prefix string, flag int) *Logger {
return &Logger{out: out, prefix: prefix, flag: flag}
}
// 设置输出.
func (l *Logger) SetOutput(w io.Writer) {
l.mu.Lock()
defer l.mu.Unlock()
l.out = w
}
var std = New(os.Stderr, "", LstdFlags)
// 该方法主要用于将整数转换为定长的十进制 ASCII，同时给出负数宽度避免左侧补 0。另外会以相反的顺序组合十进制
func itoa(buf *[]byte, i int, wid int) {
// Assemble decimal in reverse order.
var b [20]byte
bp := len(b) - 1
for i >= 10 || wid > 1 {
wid--
q := i / 10
b[bp] = byte('0' + i - q*10)
bp--
i = q
}
// i < 10
b[bp] = byte('0' + i)
*buf = append(*buf, b[bp:]...)
}
// 格式化日志头:
// * l.prefix 如果不是空值，则将 prefix 写入 buf
// * date and/or time (如果不是空值，则写入 buf),
// * file and line number (如果设置了文件和行号).
func (l *Logger) formatHeader(buf *[]byte, t time.Time, file string, line int) {
*buf = append(*buf, l.prefix...)
if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 {
if l.flag&LUTC != 0 {
t = t.UTC()
}
if l.flag&Ldate != 0 {
year, month, day := t.Date()
itoa(buf, year, 4)
*buf = append(*buf, '/')
itoa(buf, int(month), 2)
*buf = append(*buf, '/')
itoa(buf, day, 2)
*buf = append(*buf, ' ')
}
if l.flag&(Ltime|Lmicroseconds) != 0 {
hour, min, sec := t.Clock()
itoa(buf, hour, 2)
*buf = append(*buf, ':')
itoa(buf, min, 2)
*buf = append(*buf, ':')
itoa(buf, sec, 2)
if l.flag&Lmicroseconds != 0 {
*buf = append(*buf, '.')
itoa(buf, t.Nanosecond()/1e3, 6)
}
*buf = append(*buf, ' ')
}
}
if l.flag&(Lshortfile|Llongfile) != 0 {
if l.flag&Lshortfile != 0 {
short := file
for i := len(file) - 1; i > 0; i-- {
if file[i] == '/' {
short = file[i+1:]
break
}
}
file = short
}
*buf = append(*buf, file...)
*buf = append(*buf, ':')
itoa(buf, line, -1)
*buf = append(*buf, ": "...)
}
}
// Output writes the output for a logging event. The string s contains
// the text to print after the prefix specified by the flags of the
// Logger. A newline is appended if the last character of s is not
// already a newline. Calldepth is used to recover the PC and is
// provided for generality, although at the moment on all pre-defined
// paths it will be 2.
//简单讲就是组合输出信息
func (l *Logger) Output(calldepth int, s string) error {
now := time.Now() // get this early.
var file string
var line int
l.mu.Lock()
defer l.mu.Unlock()
if l.flag&(Lshortfile|Llongfile) != 0 {
// 释放锁，同时获得caller的信息-这是昂贵的。
l.mu.Unlock()
var ok bool
_, file, line, ok = runtime.Caller(calldepth)
if !ok {
file = "???"
line = 0
}
l.mu.Lock()
}
l.buf = l.buf[:0]
l.formatHeader(&l.buf, now, file, line)
l.buf = append(l.buf, s...)
if len(s) == 0 || s[len(s)-1] != '\n' {
l.buf = append(l.buf, '\n')
}
_, err := l.out.Write(l.buf)
return err
}
// Printf calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Printf.
func (l *Logger) Printf(format string, v ...interface{}) {
l.Output(2, fmt.Sprintf(format, v...))
}
// Print calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Print.
func (l *Logger) Print(v ...interface{}) { l.Output(2, fmt.Sprint(v...)) }
// Println calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Println.
func (l *Logger) Println(v ...interface{}) { l.Output(2, fmt.Sprintln(v...)) }
// Fatal is equivalent to l.Print() followed by a call to os.Exit(1).
func (l *Logger) Fatal(v ...interface{}) {
l.Output(2, fmt.Sprint(v...))
os.Exit(1)
}
// Fatalf is equivalent to l.Printf() followed by a call to os.Exit(1).
func (l *Logger) Fatalf(format string, v ...interface{}) {
l.Output(2, fmt.Sprintf(format, v...))
os.Exit(1)
}
// Fatalln is equivalent to l.Println() followed by a call to os.Exit(1).
func (l *Logger) Fatalln(v ...interface{}) {
l.Output(2, fmt.Sprintln(v...))
os.Exit(1)
}
// Panic is equivalent to l.Print() followed by a call to panic().
func (l *Logger) Panic(v ...interface{}) {
s := fmt.Sprint(v...)
l.Output(2, s)
panic(s)
}
// Panicf is equivalent to l.Printf() followed by a call to panic().
func (l *Logger) Panicf(format string, v ...interface{}) {
s := fmt.Sprintf(format, v...)
l.Output(2, s)
panic(s)
}
// Panicln is equivalent to l.Println() followed by a call to panic().
func (l *Logger) Panicln(v ...interface{}) {
s := fmt.Sprintln(v...)
l.Output(2, s)
panic(s)
}
// Flags returns the output flags for the logger.
func (l *Logger) Flags() int {
l.mu.Lock()
defer l.mu.Unlock()
return l.flag
}
// SetFlags sets the output flags for the logger.
func (l *Logger) SetFlags(flag int) {
l.mu.Lock()
defer l.mu.Unlock()
l.flag = flag
}
// Prefix returns the output prefix for the logger.
func (l *Logger) Prefix() string {
l.mu.Lock()
defer l.mu.Unlock()
return l.prefix
}
// SetPrefix sets the output prefix for the logger.
func (l *Logger) SetPrefix(prefix string) {
l.mu.Lock()
defer l.mu.Unlock()
l.prefix = prefix
}
// SetOutput sets the output destination for the standard logger.
func SetOutput(w io.Writer) {
std.mu.Lock()
defer std.mu.Unlock()
std.out = w
}
// Flags returns the output flags for the standard logger.
func Flags() int {
return std.Flags()
}
// SetFlags sets the output flags for the standard logger.
func SetFlags(flag int) {
std.SetFlags(flag)
}
// Prefix returns the output prefix for the standard logger.
func Prefix() string {
return std.Prefix()
}
// SetPrefix sets the output prefix for the standard logger.
func SetPrefix(prefix string) {
std.SetPrefix(prefix)
}
// These functions write to the standard logger.
// Print calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Print.
func Print(v ...interface{}) {
std.Output(2, fmt.Sprint(v...))
}
// Printf calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Printf.
func Printf(format string, v ...interface{}) {
std.Output(2, fmt.Sprintf(format, v...))
}
// Println calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Println.
func Println(v ...interface{}) {
std.Output(2, fmt.Sprintln(v...))
}
// Fatal is equivalent to Print() followed by a call to os.Exit(1).
func Fatal(v ...interface{}) {
std.Output(2, fmt.Sprint(v...))
os.Exit(1)
}
// Fatalf is equivalent to Printf() followed by a call to os.Exit(1).
func Fatalf(format string, v ...interface{}) {
std.Output(2, fmt.Sprintf(format, v...))
os.Exit(1)
}
// Fatalln is equivalent to Println() followed by a call to os.Exit(1).
func Fatalln(v ...interface{}) {
std.Output(2, fmt.Sprintln(v...))
os.Exit(1)
}
// Panic is equivalent to Print() followed by a call to panic().
func Panic(v ...interface{}) {
s := fmt.Sprint(v...)
std.Output(2, s)
panic(s)
}
// Panicf is equivalent to Printf() followed by a call to panic().
func Panicf(format string, v ...interface{}) {
s := fmt.Sprintf(format, v...)
std.Output(2, s)
panic(s)
}
// Panicln is equivalent to Println() followed by a call to panic().
func Panicln(v ...interface{}) {
s := fmt.Sprintln(v...)
std.Output(2, s)
panic(s)
}
// Output writes the output for a logging event. The string s contains
// the text to print after the prefix specified by the flags of the
// Logger. A newline is appended if the last character of s is not
// already a newline. Calldepth is the count of the number of
// frames to skip when computing the file name and line number
// if Llongfile or Lshortfile is set; a value of 1 will print the details
// for the caller of Output.
func Output(calldepth int, s string) error {
return std.Output(calldepth+1, s) // +1 for this frame.
}
这一段代码 有点意思
// 释放锁，同时获得caller的信息-这是昂贵的。
l.mu.Unlock()
var ok bool
_, file, line, ok = runtime.Caller(calldepth)
if !ok {
file = "???"
line = 0
}
l.mu.Lock()
}
为什么在调用 runtime.Caller 前要先解锁，后再加锁呢?
注释里说明官方也是知道runtime.Caller性能有问题。这里的Logger里带有一个Mutex锁，方便在高并发或者多协程的时候保护上下文数据一致。
这里值得借鉴的是并没有所有的日志都记录文件名和行号，而是添加了标记位flag，只有在需要的业务场景下(Lshortfile或者Llongfile )，才调用runtime.Caller，避免不必要的开支。
另外一方面，在调用性能比较差的runtime.Caller之前，把锁释放，执行完毕后再把锁加上，继续处理自己后续的业务。这个可以避免锁的时间过长，影响其他业务。
参考
https://cloud.tencent.com/developer/article/1385947
https://segmentfault.com/a/1190000016555832