adamreeve commented on code in PR #35496: URL: https://github.com/apache/arrow/pull/35496#discussion_r1222407723
########## csharp/src/Apache.Arrow/C/CArrowArrayStreamImporter.cs: ########## @@ -0,0 +1,137 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +using System; +using System.Threading; +using System.Threading.Tasks; +using Apache.Arrow.Ipc; + +namespace Apache.Arrow.C +{ + public static class CArrowArrayStreamImporter + { + /// <summary> + /// Import C pointer as an <see cref="IArrowArrayStream"/>. + /// </summary> + /// <remarks> + /// This will call the release callback on the passed struct if the function fails. + /// Otherwise, the release callback is called when the IArrowArrayStream is disposed. + /// </remarks> + /// <examples> + /// Typically, you will allocate an uninitialized CArrowArrayStream pointer, + /// pass that to external function, and then use this method to import + /// the result. + /// + /// <code> + /// CArrowArrayStream* importedPtr = CArrowArrayStream.Create(); + /// foreign_export_function(importedPtr); + /// IArrowArrayStream importedStream = CArrowArrayStreamImporter.ImportStream(importedPtr); + /// </code> + /// </examples> + public static unsafe IArrowArrayStream ImportArrayStream(CArrowArrayStream* ptr) + { + return new ImportedArrowArrayStream(ptr); + } + + private sealed unsafe class ImportedArrowArrayStream : IArrowArrayStream + { + private readonly CArrowArrayStream* _cArrayStream; + private readonly Schema _schema; + private bool _disposed; + + public ImportedArrowArrayStream(CArrowArrayStream* cArrayStream) + { + if (cArrayStream == null) + { + throw new ArgumentNullException(nameof(cArrayStream)); + } + _cArrayStream = cArrayStream; + if (_cArrayStream->release == null) + { + throw new ArgumentException("Tried to import an array stream that has already been released.", nameof(cArrayStream)); + } + + CArrowSchema* cSchema = CArrowSchema.Create(); + try + { + int errno = _cArrayStream->get_schema(_cArrayStream, cSchema); + if (errno != 0) + { + throw new Exception($"Unexpected error recieved from external stream. Errno: {errno}"); + } + _schema = CArrowSchemaImporter.ImportSchema(cSchema); + } + finally + { + if (_schema == null) + { + CArrowSchema.Free(cSchema); + } + } + } + + ~ImportedArrowArrayStream() + { + Dispose(); + } + + public Schema Schema => _schema; + + public ValueTask<RecordBatch> ReadNextRecordBatchAsync(CancellationToken cancellationToken = default) + { + if (_disposed) + { + throw new ObjectDisposedException(typeof(ImportedArrowArrayStream).Name); + } + + RecordBatch result = null; + CArrowArray* cArray = CArrowArray.Create(); Review Comment: Right, yeah having a flag to say whether the structure should be deallocated would solve both problems if it was public and implemented for both the array and stream. I think keeping the current behaviour of not deallocating makes sense as a default, given a small memory leak is less of an issue than incorrectly deallocating, and then that keeps allocation and deallocation symmetric by default. It wouldn't be a big deal if only the first problem was solved though, I can solve the second problem with some extra indirection by introducing a wrapper for the imported stream that deallocates the struct on dispose. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
