Merge pull request #827 from harshavardhana/krishnasrinivas-parallel-read2

Read from the disks in parallel during object read

pkg/donut/bucket.go

@@ -553,13 +553,31 @@ func (b bucket) decodeEncodedData(totalLeft, blockSize int64, readers map[int]io
 		return nil, err.Trace()
 	}
 	encodedBytes := make([][]byte, encoder.k+encoder.m)
+	errCh := make(chan error, len(readers))
+	var errRet error
+	var readCnt int
+
 	for i, reader := range readers {
-		var bytesBuffer bytes.Buffer
-		_, err := io.CopyN(&bytesBuffer, reader, int64(curChunkSize))
+		go func(reader io.Reader, i int) {
+			encodedBytes[i] = make([]byte, curChunkSize)
+			_, err := io.ReadFull(reader, encodedBytes[i])
+			if err != nil {
+				encodedBytes[i] = nil
+				errCh <- err
+				return
+			}
+			errCh <- nil
+		}(reader, i)
+		// read through errCh for any errors
+		err := <-errCh
 		if err != nil {
-			return nil, probe.NewError(err)
+			errRet = err
+		} else {
+			readCnt++
 		}
-		encodedBytes[i] = bytesBuffer.Bytes()
+	}
+	if readCnt < int(encoder.k) {
+		return nil, probe.NewError(errRet)
 	}
 	decodedData, err := encoder.Decode(encodedBytes, int(curBlockSize))
 	if err != nil {