feat: use read buffer to reduce read syscall

buffer.go

@@ -0,0 +1,83 @@
+package uuid
+
+import (
+	"io"
+	"sync/atomic"
+	"unsafe"
+)
+
+type buffer struct {
+	data    []byte
+	readPos int64
+}
+
+type bytesBuffer struct {
+	bufferPointer unsafe.Pointer
+	bufferSize    int
+	status        uint32
+	src           io.Reader
+}
+
+func newBytesBuffer(bufferSize int, src io.Reader) *bytesBuffer {
+	if bufferSize <= 0 || src == nil {
+		return nil
+	}
+	return &bytesBuffer{
+		bufferSize:    bufferSize,
+		bufferPointer: unsafe.Pointer(&buffer{}),
+		src:           src,
+	}
+}
+
+func (bb *bytesBuffer) reset(p []byte) {
+	atomic.StorePointer(&bb.bufferPointer, unsafe.Pointer(&buffer{
+		data:    p,
+		readPos: 0,
+	}))
+}
+
+func (bb *bytesBuffer) getBuffer() *buffer {
+	point := atomic.LoadPointer(&bb.bufferPointer)
+	return (*buffer)(point)
+}
+
+func (bb *bytesBuffer) read(dst []byte) (n int, err error) {
+	buff := bb.getBuffer()
+	readSize := (int64)(len(dst))
+	readEnd := atomic.AddInt64(&buff.readPos, readSize)
+	if readEnd > (int64)(3*len(buff.data)/4) {
+		go bb.readAhead()
+		if readEnd >= int64(len(buff.data)) {
+			return -1, io.EOF
+		}
+	}
+
+	return copy(dst, buff.data[readEnd-readSize:readEnd]), nil
+
+}
+func (bb *bytesBuffer) Read(dst []byte) (n int, err error) {
+	n, err = bb.read(dst)
+	if err != nil || n != len(dst) {
+		n, err = io.ReadFull(bb.src, dst)
+	}
+	return
+}
+
+func (bb *bytesBuffer) readAhead() (err error) {
+	if !atomic.CompareAndSwapUint32(&bb.status, 0, 1) {
+		return nil
+	}
+	defer atomic.StoreUint32(&bb.status, 0)
+
+	buf := make([]byte, bb.bufferSize)
+	readN, err := io.ReadFull(bb.src, buf[:])
+	if err != nil {
+		return err
+	}
+	if readN != bb.bufferSize {
+		return io.ErrUnexpectedEOF
+	}
+
+	bb.reset(buf)
+	return nil
+}

generator.go

@@ -102,7 +102,7 @@ func newRFC4122Generator() Generator {
 	return &rfc4122Generator{
 		epochFunc:  time.Now,
 		hwAddrFunc: defaultHWAddrFunc,
-		rand:       rand.Reader,
+		rand:       newBytesBuffer(4096, rand.Reader),
 	}
 }