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|
package buffered_writer
import (
"io"
"sync"
"time"
)
type TimedWriteBuffer struct {
maxLatencyWriterAt *maxLatencyWriterAt
bufWriterAt *bufferedWriterAt
}
func (t *TimedWriteBuffer) ReadAt(p []byte, off int64) (n int, err error) {
bufStart := t.bufWriterAt.nextOffset - int64(t.bufWriterAt.dataSize)
start := max(bufStart, off)
stop := min(t.bufWriterAt.nextOffset, off+int64(len(p)))
if start <= stop {
n = copy(p, t.bufWriterAt.data[start-bufStart:stop-bufStart])
}
return
}
func (t *TimedWriteBuffer) WriteAt(p []byte, offset int64) (n int, err error) {
return t.maxLatencyWriterAt.WriteAt(p, offset)
}
func (t *TimedWriteBuffer) Flush() {
t.maxLatencyWriterAt.Flush()
}
func (t *TimedWriteBuffer) Close() {
t.maxLatencyWriterAt.Close()
}
func NewTimedWriteBuffer(writerAt io.WriterAt, size int, latency time.Duration, currentOffset int64) *TimedWriteBuffer {
bufWriterAt := newBufferedWriterAt(writerAt, size, currentOffset)
maxLatencyWriterAt := newMaxLatencyWriterAt(bufWriterAt, latency)
return &TimedWriteBuffer{
bufWriterAt: bufWriterAt,
maxLatencyWriterAt: maxLatencyWriterAt,
}
}
type bufferedWriterAt struct {
data []byte
dataSize int
nextOffset int64
writerAt io.WriterAt
counter int
}
func newBufferedWriterAt(writerAt io.WriterAt, bufferSize int, currentOffset int64) *bufferedWriterAt {
return &bufferedWriterAt{
data: make([]byte, bufferSize),
nextOffset: currentOffset,
dataSize: 0,
writerAt: writerAt,
}
}
func (b *bufferedWriterAt) WriteAt(p []byte, offset int64) (n int, err error) {
if b.nextOffset != offset {
println("nextOffset", b.nextOffset, "bufSize", b.dataSize, "offset", offset, "data", len(p))
}
if b.nextOffset != offset || len(p)+b.dataSize > len(b.data) {
if err = b.Flush(); err != nil {
return 0, err
}
}
if len(p)+b.dataSize > len(b.data) {
n, err = b.writerAt.WriteAt(p, offset)
if err == nil {
b.nextOffset = offset + int64(n)
}
} else {
n = copy(b.data[b.dataSize:len(p)+b.dataSize], p)
b.dataSize += n
b.nextOffset += int64(n)
b.counter++
}
return
}
func (b *bufferedWriterAt) Flush() (err error) {
if b.dataSize == 0 {
return nil
}
// println("flush", b.counter)
b.counter = 0
_, err = b.writerAt.WriteAt(b.data[0:b.dataSize], b.nextOffset-int64(b.dataSize))
if err == nil {
b.dataSize = 0
}
return
}
// adapted from https://golang.org/src/net/http/httputil/reverseproxy.go
type writeFlusher interface {
io.WriterAt
Flush() error
}
type maxLatencyWriterAt struct {
dst writeFlusher
latency time.Duration // non-zero; negative means to flush immediately
mu sync.Mutex // protects t, flushPending, and dst.Flush
t *time.Timer
flushPending bool
}
func newMaxLatencyWriterAt(dst writeFlusher, latency time.Duration) *maxLatencyWriterAt {
return &maxLatencyWriterAt{
dst: dst,
latency: latency,
}
}
func (m *maxLatencyWriterAt) WriteAt(p []byte, offset int64) (n int, err error) {
m.mu.Lock()
defer m.mu.Unlock()
n, err = m.dst.WriteAt(p, offset)
if m.latency < 0 {
m.dst.Flush()
return
}
if m.flushPending {
return
}
if m.t == nil {
m.t = time.AfterFunc(m.latency, m.Flush)
} else {
m.t.Reset(m.latency)
}
m.flushPending = true
return
}
func (m *maxLatencyWriterAt) Flush() {
m.mu.Lock()
defer m.mu.Unlock()
if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
return
}
m.dst.Flush()
m.flushPending = false
}
func (m *maxLatencyWriterAt) Close() {
m.mu.Lock()
defer m.mu.Unlock()
m.flushPending = false
if m.t != nil {
m.t.Stop()
}
}
func min(x, y int64) int64 {
if x <= y {
return x
}
return y
}
func max(x, y int64) int64 {
if x <= y {
return y
}
return x
}
|
