worryg0d commented on code in PR #1946:
URL:
https://github.com/apache/cassandra-gocql-driver/pull/1946#discussion_r3273078597
##########
conn.go:
##########
@@ -2047,6 +1937,343 @@ func (c *Conn) awaitSchemaAgreementWithTimeout(ctx
context.Context, timeout time
return fmt.Errorf("gocql: cluster schema versions not consistent: %+v",
schemas)
}
+// segmentWriter allows batching multiple frames into a signle segment before
flushing them to the connection.
+type segmentWriter struct {
+ w contextWriter
+ quit <-chan struct{}
+
+ // Holds write requests for the current segment.
+ writeRequests []writeRequest
+ totalFramesLength int
+ writeCh chan writeRequest
+
+ segmentCodec segmentCodec
+}
+
+func newSegmentWriter(w contextWriter, writeInterval time.Duration, quit
<-chan struct{}, compressor Compressor) *segmentWriter {
+ sw := &segmentWriter{
+ w: w,
+ quit: quit,
+ writeCh: make(chan writeRequest),
+ segmentCodec: newSegmentCodec(compressor),
+ }
+
+ go sw.runFlusher(writeInterval)
+
+ return sw
+}
+
+func (sw *segmentWriter) writeContext(ctx context.Context, frame []byte) (int,
error) {
+ resultChan := make(chan writeResult, 1)
+ req := writeRequest{
+ resultChan: resultChan,
+ data: frame,
+ }
+
+ select {
+ case <-ctx.Done():
+ return 0, ctx.Err()
+ case <-sw.quit:
+ return 0, ErrConnectionClosed
+ case sw.writeCh <- req:
+ // Enqueued for writing
+ }
+
+ result := <-resultChan
+ return result.n, result.err
+}
+
+func (sw *segmentWriter) runFlusher(interval time.Duration) {
+ timer := time.NewTimer(interval)
+ defer timer.Stop()
+
+ if !timer.Stop() {
+ <-timer.C
+ }
+
+ // Indicates whether the flush timer is running
+ running := false
+
+ for {
+ select {
+ case <-sw.quit:
+ return
+ case req := <-sw.writeCh:
+ frame := req.data
+ if len(frame) > maxSegmentPayloadSize {
+ sw.flushBigFrameImmediately(req)
+ } else if sw.fitsSegment(frame) {
+ sw.appendWriteRequest(req)
+ if !running {
+ running = true
+ timer.Reset(interval)
+ }
+ } else {
+ // Frame doesn't fit into current segment,
+ // so we need to flush the current one and
start a new one
+ sw.flushCurrentSegment()
+ sw.reset()
+ sw.appendWriteRequest(req)
+ timer.Reset(interval)
+ }
+ case <-timer.C:
+ running = false
+ sw.flushCurrentSegment()
+ sw.reset()
+ }
+ }
+}
+
+func (sw *segmentWriter) appendWriteRequest(req writeRequest) {
+ sw.writeRequests = append(sw.writeRequests, req)
+ sw.totalFramesLength += len(req.data)
+}
+
+func (sw *segmentWriter) fitsSegment(frame []byte) bool {
+ return sw.totalFramesLength+len(frame) <= maxSegmentPayloadSize
+}
+
+// Flushes the current segment and writes the results to the result listeners.
+// Should be called before resetting the segment writer.
+func (sw *segmentWriter) flushCurrentSegment() {
+ framesBuf := make([]byte, 0, sw.totalFramesLength)
+ for _, req := range sw.writeRequests {
+ // TODO: interesting if compiler optimizes this
+ framesBuf = append(framesBuf, req.data...)
+ }
+
+ err := sw.encodeAndWrite(framesBuf, true)
+ if err != nil {
+ for _, req := range sw.writeRequests {
+ req.resultChan <- writeResult{
+ n: 0,
+ err: err,
+ }
+ }
+ return
+ }
+
+ for _, req := range sw.writeRequests {
+ req.resultChan <- writeResult{
+ n: len(req.data),
+ err: nil,
+ }
+ }
+}
+
+func (sw *segmentWriter) reset() {
+ sw.writeRequests = nil
+ sw.totalFramesLength = 0
+}
+
+// Encodes a big frame which size is larger than maxSegmentPayloadSize
+// into multiple non self-contained segments and flushes them immediately
+func (sw *segmentWriter) flushBigFrameImmediately(req writeRequest) {
+ // Calculate the number of segment the frame will be split into
+ segmentsCount := 0
+ frame := req.data
+ frameLength := len(frame)
+ exactFit := frameLength%maxSegmentPayloadSize == 0
+ if exactFit {
+ segmentsCount = frameLength / maxSegmentPayloadSize
+ } else {
+ // An extra segment for the remainder of the frame
+ segmentsCount = frameLength/maxSegmentPayloadSize + 1
+ }
+
+ var flushErr error
+
+ for i := 0; i < segmentsCount; i++ {
+ // Calculate the length of the current frame part which will be
encoded into a segment
+ partialFrameLength := 0
+ if i < segmentsCount-1 || exactFit {
+ partialFrameLength = maxSegmentPayloadSize
+ } else {
+ partialFrameLength = frameLength % maxSegmentPayloadSize
+ }
+ err := sw.encodeAndWrite(frame[:partialFrameLength], false)
+ if err != nil {
+ flushErr = err
+ break
+ }
+ frame = frame[partialFrameLength:]
+ }
+
+ written := len(req.data)
+ if flushErr != nil {
+ written = 0
+ }
+
+ req.resultChan <- writeResult{
+ n: written,
+ err: flushErr,
+ }
+}
+
+// Encodes a frame into a segment and writes it to the underlying connection
+func (sw *segmentWriter) encodeAndWrite(frame []byte, isSelfContained bool)
error {
+ segmentBuf, err := sw.segmentCodec.encode(frame, isSelfContained)
+ if err != nil {
+ return err
+ }
+ _, err = sw.w.writeContext(context.Background(), segmentBuf)
+ if err != nil {
+ return err
+ }
+ return nil
+}
+
+// segmentReader allows reading segments from the underlying connection.
+// Implements ConnReader interface.
+type segmentReader struct {
+ r ConnReader
+
+ segmentCodec segmentCodec
+
+ // Reusable buffer for decoded frames
+ // This buffer might have multiple frames inside if self-contained
segment is decoded
+ readBufferDecoded bytes.Reader
+ // Reusable buffer for reading frame header
+ frameHeaderBuf [frameHeadSize]byte
+}
+
+func newSegmentReader(r ConnReader, segmentCodec segmentCodec) *segmentReader {
+ return &segmentReader{
+ r: r,
+ segmentCodec: segmentCodec,
+ }
+}
+
+// why do we have a write method for reader lol
Review Comment:
ConnReader is public, but it is very unlikely anybody relies on this, imo,
as there is nothing in the driver that implements this interface and is
exported. We probably just have to make it private
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