github.com/hasnat/dolt/go@v0.0.0-20210628190320-9eb5d843fbb7/libraries/doltcore/table/read_ahead_table_reader.go (about) 1 // Copyright 2020 Dolthub, Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package table 16 17 import ( 18 "context" 19 20 "github.com/dolthub/dolt/go/libraries/doltcore/row" 21 "github.com/dolthub/dolt/go/libraries/doltcore/schema" 22 "github.com/dolthub/dolt/go/libraries/utils/async" 23 ) 24 25 var _ TableReadCloser = (*AsyncReadAheadTableReader)(nil) 26 27 // AsyncReadAheadTableReader is a TableReadCloser implementation that spins up a go routine to keep reading data into 28 // a buffered channel so that it is ready when the caller wants it. 29 type AsyncReadAheadTableReader struct { 30 backingReader TableReadCloser 31 reader *async.AsyncReader 32 } 33 34 // NewAsyncReadAheadTableReader creates a new AsyncReadAheadTableReader 35 func NewAsyncReadAheadTableReader(tr TableReadCloser, bufferSize int) *AsyncReadAheadTableReader { 36 read := func(ctx context.Context) (interface{}, error) { 37 return tr.ReadRow(ctx) 38 } 39 40 reader := async.NewAsyncReader(read, bufferSize) 41 return &AsyncReadAheadTableReader{tr, reader} 42 } 43 44 // Start the worker routine reading rows to the channel 45 func (tr *AsyncReadAheadTableReader) Start(ctx context.Context) error { 46 return tr.reader.Start(ctx) 47 } 48 49 // GetSchema gets the schema of the rows that this reader will return 50 func (tr *AsyncReadAheadTableReader) GetSchema() schema.Schema { 51 return tr.backingReader.GetSchema() 52 } 53 54 // ReadRow reads a row from a table. If there is a bad row the returned error will be non nil, and calling 55 // IsBadRow(err) will be return true. This is a potentially non-fatal error and callers can decide if they want to 56 // continue on a bad row, or fail. 57 func (tr *AsyncReadAheadTableReader) ReadRow(ctx context.Context) (row.Row, error) { 58 obj, err := tr.reader.Read() 59 60 if err != nil { 61 return nil, err 62 } 63 64 return obj.(row.Row), err 65 } 66 67 // Close releases resources being held 68 func (tr *AsyncReadAheadTableReader) Close(ctx context.Context) error { 69 _ = tr.reader.Close() 70 return tr.backingReader.Close(ctx) 71 }