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moby--moby/pkg/ioutils/bytespipe.go

187 lines
4.2 KiB
Go

package ioutils // import "github.com/docker/docker/pkg/ioutils"
import (
"errors"
"io"
"sync"
)
// maxCap is the highest capacity to use in byte slices that buffer data.
const maxCap = 1e6
// minCap is the lowest capacity to use in byte slices that buffer data
const minCap = 64
// blockThreshold is the minimum number of bytes in the buffer which will cause
// a write to BytesPipe to block when allocating a new slice.
const blockThreshold = 1e6
var (
// ErrClosed is returned when Write is called on a closed BytesPipe.
ErrClosed = errors.New("write to closed BytesPipe")
bufPools = make(map[int]*sync.Pool)
bufPoolsLock sync.Mutex
)
// BytesPipe is io.ReadWriteCloser which works similarly to pipe(queue).
// All written data may be read at most once. Also, BytesPipe allocates
// and releases new byte slices to adjust to current needs, so the buffer
// won't be overgrown after peak loads.
type BytesPipe struct {
mu sync.Mutex
wait *sync.Cond
buf []*fixedBuffer
bufLen int
closeErr error // error to return from next Read. set to nil if not closed.
}
// NewBytesPipe creates new BytesPipe, initialized by specified slice.
// If buf is nil, then it will be initialized with slice which cap is 64.
// buf will be adjusted in a way that len(buf) == 0, cap(buf) == cap(buf).
func NewBytesPipe() *BytesPipe {
bp := &BytesPipe{}
bp.buf = append(bp.buf, getBuffer(minCap))
bp.wait = sync.NewCond(&bp.mu)
return bp
}
// Write writes p to BytesPipe.
// It can allocate new []byte slices in a process of writing.
func (bp *BytesPipe) Write(p []byte) (int, error) {
bp.mu.Lock()
written := 0
loop0:
for {
if bp.closeErr != nil {
bp.mu.Unlock()
return written, ErrClosed
}
if len(bp.buf) == 0 {
bp.buf = append(bp.buf, getBuffer(64))
}
// get the last buffer
b := bp.buf[len(bp.buf)-1]
n, err := b.Write(p)
written += n
bp.bufLen += n
// errBufferFull is an error we expect to get if the buffer is full
if err != nil && err != errBufferFull {
bp.wait.Broadcast()
bp.mu.Unlock()
return written, err
}
// if there was enough room to write all then break
if len(p) == n {
break
}
// more data: write to the next slice
p = p[n:]
// make sure the buffer doesn't grow too big from this write
for bp.bufLen >= blockThreshold {
bp.wait.Wait()
if bp.closeErr != nil {
continue loop0
}
}
// add new byte slice to the buffers slice and continue writing
nextCap := b.Cap() * 2
if nextCap > maxCap {
nextCap = maxCap
}
bp.buf = append(bp.buf, getBuffer(nextCap))
}
bp.wait.Broadcast()
bp.mu.Unlock()
return written, nil
}
// CloseWithError causes further reads from a BytesPipe to return immediately.
func (bp *BytesPipe) CloseWithError(err error) error {
bp.mu.Lock()
if err != nil {
bp.closeErr = err
} else {
bp.closeErr = io.EOF
}
bp.wait.Broadcast()
bp.mu.Unlock()
return nil
}
// Close causes further reads from a BytesPipe to return immediately.
func (bp *BytesPipe) Close() error {
return bp.CloseWithError(nil)
}
// Read reads bytes from BytesPipe.
// Data could be read only once.
func (bp *BytesPipe) Read(p []byte) (n int, err error) {
bp.mu.Lock()
if bp.bufLen == 0 {
if bp.closeErr != nil {
err := bp.closeErr
bp.mu.Unlock()
return 0, err
}
bp.wait.Wait()
if bp.bufLen == 0 && bp.closeErr != nil {
err := bp.closeErr
bp.mu.Unlock()
return 0, err
}
}
for bp.bufLen > 0 {
b := bp.buf[0]
read, _ := b.Read(p) // ignore error since fixedBuffer doesn't really return an error
n += read
bp.bufLen -= read
if b.Len() == 0 {
// it's empty so return it to the pool and move to the next one
returnBuffer(b)
bp.buf[0] = nil
bp.buf = bp.buf[1:]
}
if len(p) == read {
break
}
p = p[read:]
}
bp.wait.Broadcast()
bp.mu.Unlock()
return
}
func returnBuffer(b *fixedBuffer) {
b.Reset()
bufPoolsLock.Lock()
pool := bufPools[b.Cap()]
bufPoolsLock.Unlock()
if pool != nil {
pool.Put(b)
}
}
func getBuffer(size int) *fixedBuffer {
bufPoolsLock.Lock()
pool, ok := bufPools[size]
if !ok {
pool = &sync.Pool{New: func() interface{} { return &fixedBuffer{buf: make([]byte, 0, size)} }}
bufPools[size] = pool
}
bufPoolsLock.Unlock()
return pool.Get().(*fixedBuffer)
}