115 lines
2.6 KiB
Go
115 lines
2.6 KiB
Go
// Package diode provides a thread-safe, lock-free, non-blocking io.Writer
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// wrapper.
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package diode
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import (
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"context"
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"io"
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"sync"
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"time"
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"git.tuxpa.in/a/zlog/diode/internal/diodes"
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)
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var bufPool = &sync.Pool{
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New: func() interface{} {
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return make([]byte, 0, 500)
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},
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}
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type Alerter func(missed int)
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type diodeFetcher interface {
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diodes.Diode
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Next() diodes.GenericDataType
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}
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// Writer is a io.Writer wrapper that uses a diode to make Write lock-free,
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// non-blocking and thread safe.
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type Writer struct {
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w io.Writer
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d diodeFetcher
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c context.CancelFunc
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done chan struct{}
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}
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// NewWriter creates a writer wrapping w with a many-to-one diode in order to
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// never block log producers and drop events if the writer can't keep up with
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// the flow of data.
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//
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// Use a diode.Writer when
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//
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// wr := diode.NewWriter(w, 1000, 0, func(missed int) {
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// log.Printf("Dropped %d messages", missed)
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// })
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// log := zlog.New(wr)
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//
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// If pollInterval is greater than 0, a poller is used otherwise a waiter is
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// used.
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//
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// See code.cloudfoundry.org/go-diodes for more info on diode.
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func NewWriter(w io.Writer, size int, pollInterval time.Duration, f Alerter) Writer {
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ctx, cancel := context.WithCancel(context.Background())
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dw := Writer{
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w: w,
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c: cancel,
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done: make(chan struct{}),
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}
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if f == nil {
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f = func(int) {}
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}
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d := diodes.NewManyToOne(size, diodes.AlertFunc(f))
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if pollInterval > 0 {
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dw.d = diodes.NewPoller(d,
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diodes.WithPollingInterval(pollInterval),
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diodes.WithPollingContext(ctx))
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} else {
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dw.d = diodes.NewWaiter(d,
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diodes.WithWaiterContext(ctx))
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}
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go dw.poll()
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return dw
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}
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func (dw Writer) Write(p []byte) (n int, err error) {
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// p is pooled in zlog so we can't hold it passed this call, hence the
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// copy.
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p = append(bufPool.Get().([]byte), p...)
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dw.d.Set(diodes.GenericDataType(&p))
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return len(p), nil
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}
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// Close releases the diode poller and call Close on the wrapped writer if
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// io.Closer is implemented.
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func (dw Writer) Close() error {
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dw.c()
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<-dw.done
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if w, ok := dw.w.(io.Closer); ok {
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return w.Close()
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}
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return nil
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}
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func (dw Writer) poll() {
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defer close(dw.done)
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for {
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d := dw.d.Next()
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if d == nil {
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return
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}
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p := *(*[]byte)(d)
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dw.w.Write(p)
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// Proper usage of a sync.Pool requires each entry to have approximately
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// the same memory cost. To obtain this property when the stored type
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// contains a variably-sized buffer, we add a hard limit on the maximum buffer
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// to place back in the pool.
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//
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// See https://golang.org/issue/23199
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const maxSize = 1 << 16 // 64KiB
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if cap(p) <= maxSize {
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bufPool.Put(p[:0])
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}
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}
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}
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