聊聊golang的zap的CheckedEntry

序

本文主要研究一下golang的zap的CheckedEntry

Entry

zap@v1.16.0/zapcore/entry.go

type Entry struct {
    Level      Level
    Time       time.Time
    LoggerName string
    Message    string
    Caller     EntryCaller
    Stack      string
}

Entry定义了Level、Time、LoggerName、Message、Caller、Stack属性

CheckedEntry

zap@v1.16.0/zapcore/entry.go

type CheckedEntry struct {
    Entry
    ErrorOutput WriteSyncer
    dirty       bool // best-effort detection of pool misuse
    should      CheckWriteAction
    cores       []Core
}

CheckedEntry内嵌了Entry，定义了ErrorOutput、dirty、CheckWriteAction、cores属性

reset

zap@v1.16.0/zapcore/entry.go

func (ce *CheckedEntry) reset() {
    ce.Entry = Entry{}
    ce.ErrorOutput = nil
    ce.dirty = false
    ce.should = WriteThenNoop
    for i := range ce.cores {
        // don't keep references to cores
        ce.cores[i] = nil
    }
    ce.cores = ce.cores[:0]
}

reset会重置CheckedEntry的Entry、ErrorOutput、dirty、CheckWriteAction、cores属性

Write

zap@v1.16.0/zapcore/entry.go

func (ce *CheckedEntry) Write(fields ...Field) {
    if ce == nil {
        return
    }

    if ce.dirty {
        if ce.ErrorOutput != nil {
            // Make a best effort to detect unsafe re-use of this CheckedEntry.
            // If the entry is dirty, log an internal error; because the
            // CheckedEntry is being used after it was returned to the pool,
            // the message may be an amalgamation from multiple call sites.
            fmt.Fprintf(ce.ErrorOutput, "%v Unsafe CheckedEntry re-use near Entry %+v.\n", time.Now(), ce.Entry)
            ce.ErrorOutput.Sync()
        }
        return
    }
    ce.dirty = true

    var err error
    for i := range ce.cores {
        err = multierr.Append(err, ce.cores[i].Write(ce.Entry, fields))
    }
    if ce.ErrorOutput != nil {
        if err != nil {
            fmt.Fprintf(ce.ErrorOutput, "%v write error: %v\n", time.Now(), err)
            ce.ErrorOutput.Sync()
        }
    }

    should, msg := ce.should, ce.Message
    putCheckedEntry(ce)

    switch should {
    case WriteThenPanic:
        panic(msg)
    case WriteThenFatal:
        exit.Exit()
    case WriteThenGoexit:
        runtime.Goexit()
    }
}

Write方法先判断CheckedEntry是否是dirty，如果是则表示该entry复用出问题了，就往ErrorOutput输出错误信息，然后返回；不是dirty的话，就先标注为dirty，然后遍历cores挨个执行core的Write方法，并用multierr来记录错误，如果出现err且ErrorOutput不为nil则往ErrorOutput输出err信息；之后执行putCheckedEntry放入_cePool中，最后根据CheckWriteAction来执行对应的操作

AddCore

zap@v1.16.0/zapcore/entry.go

func (ce *CheckedEntry) AddCore(ent Entry, core Core) *CheckedEntry {
    if ce == nil {
        ce = getCheckedEntry()
        ce.Entry = ent
    }
    ce.cores = append(ce.cores, core)
    return ce
}

AddCore往CheckedEntry的cores添加core，相当于多添加一个输出

Should

zap@v1.16.0/zapcore/entry.go

func (ce *CheckedEntry) Should(ent Entry, should CheckWriteAction) *CheckedEntry {
    if ce == nil {
        ce = getCheckedEntry()
        ce.Entry = ent
    }
    ce.should = should
    return ce
}

Should用于更新CheckedEntry的CheckWriteAction

_cePool

zap@v1.16.0/zapcore/entry.go

var (
    _cePool = sync.Pool{New: func() interface{} {
        // Pre-allocate some space for cores.
        return &CheckedEntry{
            cores: make([]Core, 4),
        }
    }}
)

func getCheckedEntry() *CheckedEntry {
    ce := _cePool.Get().(*CheckedEntry)
    ce.reset()
    return ce
}

func putCheckedEntry(ce *CheckedEntry) {
    if ce == nil {
        return
    }
    _cePool.Put(ce)
}

_cePool为CheckedEntry的Pool，其New函数创建cores长度为4的CheckedEntry；其getCheckedEntry方法从_cePool取出一个CheckedEntry，然后执行reset，再返回；其putCheckedEntry方法将CheckedEntry归还到_cePool中

实例

func checkedEntryDemo() {
    entry := zapcore.Entry{
        Level:      zapcore.InfoLevel,
        Time:       time.Now(),
        LoggerName: "demoLogger",
        Message:    "hello world",
        Caller:     zapcore.NewEntryCaller(100, "/path/to/foo.go", 42, false),
        Stack:      "this is stack",
    }
    ce := &zapcore.CheckedEntry{
        Entry:       entry,
        ErrorOutput: zapcore.Lock(os.Stderr),
    }

    buf := &bytes.Buffer{}
    core := zapcore.NewCore(zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()), zapcore.AddSync(buf), zap.InfoLevel)

    ce.AddCore(entry, core)
    ce.Write()
    fmt.Print(buf)
}

输出

{"level":"info","ts":1608133564.1996229,"logger":"demoLogger","msg":"hello world","stacktrace":"this is stack"}

小结

CheckedEntry内嵌了Entry，定义了ErrorOutput、dirty、CheckWriteAction、cores属性；entry包使用_cePool来获取和归还CheckedEntry；CheckedEntry提供了AddCore方法往CheckedEntry的cores添加core，其Write会遍历cores挨个执行core的Write方法，其reset方法用于在从pool中取出CheckedEntry时重置其属性。

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