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buffered_writer.go
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/
buffered_writer.go
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package parallelwriter
import (
"container/list"
"errors"
"io"
"sync"
"github.com/akmistry/go-util/ringbuffer"
)
var (
ErrClosed = errors.New("buffered_writer: closed")
)
type WriteFlusher interface {
io.Writer
Flush() error
}
type nopFlusher struct {
io.Writer
}
func NopFlusher(w io.Writer) WriteFlusher {
return &nopFlusher{w}
}
func (*nopFlusher) Flush() error { return nil }
type bufferedOp struct {
length int
}
type flushOp struct {
done chan struct{}
err error
}
type bufOp struct {
buf []byte
done chan struct{}
n int
err error
}
type BufferedWriter struct {
w WriteFlusher
rb *ringbuffer.RingBuffer
closed bool
err error
ops list.List
lock sync.Mutex
cond *sync.Cond
}
func NewBufferedWriter(w WriteFlusher, bufferSize int) *BufferedWriter {
b := &BufferedWriter{
w: w,
}
if bufferSize > 0 {
b.rb = ringbuffer.NewRingBuffer(make([]byte, bufferSize))
}
b.cond = sync.NewCond(&b.lock)
go b.flusher()
return b
}
func (b *BufferedWriter) doOp(op interface{}) error {
switch o := op.(type) {
case *bufferedOp:
n := 0
for n < o.length {
buf := b.rb.Peek(0)
writeSize := o.length - n
if writeSize > len(buf) {
writeSize = len(buf)
}
b.lock.Unlock()
written, err := b.w.Write(buf[:writeSize])
b.lock.Lock()
n += written
b.rb.Consume(written)
if err != nil {
return err
}
}
return nil
case *flushOp:
b.lock.Unlock()
o.err = b.w.Flush()
b.lock.Lock()
close(o.done)
return o.err
case *bufOp:
b.lock.Unlock()
o.n, o.err = b.w.Write(o.buf)
b.lock.Lock()
close(o.done)
return o.err
default:
panic("unsupported op type")
}
}
func (b *BufferedWriter) flusher() {
b.lock.Lock()
defer b.lock.Unlock()
for b.err == nil && !b.closed {
if b.ops.Len() == 0 {
b.cond.Wait()
}
for b.ops.Len() > 0 && b.err == nil && !b.closed {
op := b.ops.Remove(b.ops.Back())
err := b.doOp(op)
if err != nil {
b.err = err
}
}
}
err := b.err
if err == nil {
err = ErrClosed
}
for b.ops.Len() > 0 {
op := b.ops.Remove(b.ops.Back())
switch o := op.(type) {
case *flushOp:
o.err = err
defer close(o.done)
case *bufOp:
o.err = err
defer close(o.done)
}
}
}
// Close closes the writer and prevents any new writes from succeeding. This
// does not close the underlying writer which must be closed to ensure any
// pending writes are canceled. It must be safe to close the underlying writer
// from a different goroutine than an active Write.
//
// Close does not block.
func (b *BufferedWriter) Close() error {
b.lock.Lock()
defer b.lock.Unlock()
b.closed = true
b.cond.Signal()
return b.err
}
func (b *BufferedWriter) writeBlocking(buf []byte) (int, error) {
bo := &bufOp{buf: buf, done: make(chan struct{})}
b.ops.PushFront(bo)
b.cond.Signal()
b.lock.Unlock()
<-bo.done
b.lock.Lock()
return bo.n, bo.err
}
func (b *BufferedWriter) Write(buf []byte) (int, error) {
b.lock.Lock()
defer b.lock.Unlock()
if b.err != nil {
return 0, b.err
} else if b.closed {
return 0, ErrClosed
}
if b.rb == nil || len(buf) > b.rb.Free() {
return b.writeBlocking(buf)
}
var bo *bufferedOp
head := b.ops.Front()
if head != nil {
bo, _ = head.Value.(*bufferedOp)
}
if bo == nil {
bo = new(bufferedOp)
b.ops.PushFront(bo)
b.cond.Signal()
}
bo.length += len(buf)
n, err := b.rb.Append(buf)
if err != nil {
panic(err)
}
return n, err
}
func (b *BufferedWriter) Flush() error {
b.lock.Lock()
defer b.lock.Unlock()
if b.err != nil {
return b.err
} else if b.closed {
return ErrClosed
}
var fo *flushOp
head := b.ops.Front()
if head != nil {
fo, _ = head.Value.(*flushOp)
}
if fo == nil {
fo = &flushOp{done: make(chan struct{})}
b.ops.PushFront(fo)
b.cond.Signal()
}
b.lock.Unlock()
<-fo.done
b.lock.Lock()
return fo.err
}