wjones127 commented on code in PR #34133: URL: https://github.com/apache/arrow/pull/34133#discussion_r1132958403
########## csharp/src/Apache.Arrow/C/CArrowSchema.cs: ########## @@ -0,0 +1,122 @@ +// 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.Runtime.InteropServices; +using Apache.Arrow.Types; + +namespace Apache.Arrow.C +{ + /// <summary> + /// An Arrow C Data Interface Schema, which represents a type, field, or schema. + /// </summary> + /// + /// <remarks> + /// This is used to export <see cref="ArrowType"/>, <see cref="Field"/>, or + /// <see cref="Schema"/> to other languages. It matches the layout of the + /// ArrowSchema struct described in https://github.com/apache/arrow/blob/main/cpp/src/arrow/c/abi.h. + /// </remarks> + [StructLayout(LayoutKind.Sequential)] + public unsafe struct CArrowSchema + { + public byte* format; + public byte* name; + public byte* metadata; + public long flags; + public long n_children; + public CArrowSchema** children; + public CArrowSchema* dictionary; + public delegate* unmanaged[Stdcall]<CArrowSchema*, void> release; + public void* private_data; + + + public static unsafe CArrowSchema* New() + { + var ptr = (CArrowSchema*)Marshal.AllocHGlobal(Marshal.SizeOf<CArrowSchema>()); + + ptr->format = null; + ptr->name = null; + ptr->metadata = null; + ptr->flags = 0; + ptr->n_children = 0; + ptr->children = null; + ptr->dictionary = null; + ptr->release = null; + ptr->private_data = null; + + return ptr; + } + + /// <summary> + /// Free a pointer that was allocated in <see cref="AllocateAsPtr"/>. + /// </summary> + /// <remarks> + /// Do not call this on a pointer that was allocated elsewhere. + /// </remarks> + public static unsafe void Free(CArrowSchema* schema) + { + if (schema->release != null) + { + // Call release if not already called. + schema->release(schema); + } + Marshal.FreeHGlobal((IntPtr)schema); + } + + + /// <summary> + /// Whether this field is semantically nullable (regardless of whether it actually has null values) + /// </summary> + public const long ArrowFlagDictionaryOrdered = 1; + /// <summary> + /// For dictionary-encoded types, whether the ordering of dictionary indices is semantically meaningful. + /// </summary> + public const long ArrowFlagNullable = 2; + /// <summary> + /// For map types, whether the keys within each map value are sorted. + /// </summary> + public const long ArrowFlagMapKeysSorted = 4; + + /// <summary> + /// Get the value of a particular flag. + /// </summary> + /// <remarks> + /// Known valid flags are <see cref="ArrowFlagDictionaryOrdered" />, + /// <see cref="ArrowFlagNullable" />, and <see cref="ArrowFlagMapKeysSorted" />. + /// </remarks> + public bool GetFlag(long flag) + { + return (flags & flag) == flag; + } + + internal CArrowSchema* GetChild(int i) Review Comment: I thought about exposing it, but got worried it could be misused easily. If someone where to try to import a child schema instead of the root `CArrowSchema`, they would call the wrong release callback. Consumers "MUST not call any of its children’s release callbacks (including the optional dictionary)". See https://arrow.apache.org/docs/format/CDataInterface.html#release-callback-semantics-for-consumers -- 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]
