davisusanibar commented on code in PR #12794: URL: https://github.com/apache/arrow/pull/12794#discussion_r845199308
########## docs/source/java/cdata.rst: ########## @@ -0,0 +1,313 @@ +.. 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. + +================ +C Data Interface +================ + +.. contents:: + +Arrow supports exchanging data within the same process through the :ref:`c-data-interface`. + +Java to Python +-------------- + +Use this guide to implement :doc:`Java to Python <../python/integration/python_java.rst>` +communication using the C Data Interface. + +Java to C++ +----------- + +The C Data Interface is a protocol implemented in Arrow to exchange data within different +environments without the cost of marshaling and copying data. + +Example: How to expose an int32 array using C Data Interface? + +**C++ Side** + +Compile arrow minimal library: + +.. code-block:: shell + + git clone https://github.com/apache/arrow.git + cd arrow/cpp + cmake --preset -N ninja-debug-minimal + mkdir build # from inside the `cpp` subdirectory + cd build + cmake .. --preset ninja-debug-minimal + cmake --build . + tree debug/ + debug/ + ├── libarrow.800.0.0.dylib + ├── libarrow.800.dylib -> libarrow.800.0.0.dylib + └── libarrow.dylib -> libarrow.800.dylib + +Define c++ code CDataInterfaceLibrary.h that export functions for third party like Java consumer: + +.. code-block:: cpp + + #include <iostream> + #include <arrow/api.h> + + #define ARROW_FLAG_DICTIONARY_ORDERED 1 + #define ARROW_FLAG_NULLABLE 2 + #define ARROW_FLAG_MAP_KEYS_SORTED 4 + + using arrow::Int64Builder; + + struct ArrowSchema { + // Array type description + const char* format; + const char* name; + const char* metadata; + int64_t flags; + int64_t n_children; + struct ArrowSchema** children; + struct ArrowSchema* dictionary; + + // Release callback + void (*release)(struct ArrowSchema*); + // Opaque producer-specific data + void* private_data; + }; + + struct ArrowArray { + // Array data description + int64_t length; + int64_t null_count; + int64_t offset; + int64_t n_buffers; + int64_t n_children; + const void** buffers; + struct ArrowArray** children; + struct ArrowArray* dictionary; + + // Release callback + void (*release)(struct ArrowArray*); + // Opaque producer-specific data + void* private_data; + }; + + static void release_int32_type(struct ArrowSchema* schema) { + // Mark released + schema->release = NULL; + } + + void export_int32_type(struct ArrowSchema* schema) { + *schema = (struct ArrowSchema) { + // Type description + .format = "l", + .name = "", + .metadata = NULL, + .flags = 0, + .n_children = 0, + .children = NULL, + .dictionary = NULL, + // Bookkeeping + .release = &release_int32_type + }; + std::cout << "C Data - Schema Pointer = " << schema << std::endl; + } + + static void release_int32_array(struct ArrowArray* array) { + assert(array->n_buffers == 2); + // Free the buffers and the buffers array + free((void *) array->buffers[1]); + free(array->buffers); + // Mark released + array->release = NULL; + } + + void export_int32_array(struct ArrowArray* array) { + arrow::Int64Builder builder; + builder.Append(1); + builder.Append(2); + builder.Append(3); + builder.AppendNull(); + builder.Append(5); + builder.Append(6); + builder.Append(7); + builder.Append(8); + + auto maybe_array = builder.Finish(); + std::shared_ptr<arrow::Array> array_arrow = *maybe_array; + auto int64_array = std::static_pointer_cast<arrow::Int64Array>(array_arrow); + const int64_t* data = int64_array->raw_values(); + std::cout << "Data To Exchange Pointer = " << data << std::endl; + for (int j = 0; j < int64_array->length(); j++){ + std::cout << "Data To Exchange Value[" << j << "] = " << data[j] << std::endl; + } + + *array = (struct ArrowArray) { + // Data description + .length = int64_array->length(), + .offset = 0, + .null_count = 0, + .n_buffers = 2, + .n_children = 0, + .children = NULL, + .dictionary = NULL, + // Bookkeeping + .release = &release_int32_array + }; + + // Allocate list of buffers + array->buffers = (const void**) malloc(sizeof(void*) * array->n_buffers); + assert(array->buffers != NULL); + array->buffers[0] = NULL; // no nulls, null bitmap can be omitted + array->buffers[1] = data; + + std::cout << "C Data - Array Pointer = " << array << std::endl; + std::cout << "C Data - Array Data Pointer Buffer array->buffers[1] = " << array->buffers[1] << std::endl; + } + +**Java Side** + +Define Java code CDataInterfaceLibraryConfig.java that consume by JNI C++ functions exported through +C Data Interface: Review Comment: Added -- This is an automated message from the Apache Git Service. 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