vibhatha commented on code in PR #325: URL: https://github.com/apache/arrow-cookbook/pull/325#discussion_r1316145455
########## java/source/cdata.rst: ########## @@ -0,0 +1,507 @@ +.. 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 +================ + +Recipes related to how to exchange data using C Data Interface specification. + +.. contents:: + +Python (Consumer) - Java (Producer) +=================================== + + For Python Consumer and Java Producer, please consider: + + - The Root Allocator should be shared for all memory allocations. + + - The Python application will sometimes shut down the Java JVM but Java JNI C Data will still work on releasing exported objects, which is why some guards have been implemented to protect against such scenarios. A warning message "WARNING: Failed to release Java C Data resource" indicates this scenario. + + - We do not know when Root Allocator will be closed. It is for this reason that the Root Allocator should survive so long as the export/import of used objects is released. Here is an example of this scenario: + + + Whenever Java code calls `allocator.close`, a memory leak will occur since many objects will have to be released on either Python or Java JNI sides. + + + To solve memory leak problems, you will call Java `allocator.close` when Python and Java JNI have released all their objects, which is impossible to accomplish. + + - In addition, Java applications should expose a method for closing all Java-created objects independently from Root Allocators. + + +Sharing ValueVector +******************* + +Java Side: + +.. testcode:: + + import org.apache.arrow.c.ArrowArray; + import org.apache.arrow.c.ArrowSchema; + import org.apache.arrow.c.Data; + import org.apache.arrow.memory.BufferAllocator; + import org.apache.arrow.memory.RootAllocator; + import org.apache.arrow.util.AutoCloseables; + import org.apache.arrow.vector.FieldVector; + import org.apache.arrow.vector.IntVector; + + public class ShareValueVectorAPI { + final static BufferAllocator allocator = new RootAllocator(); + final static IntVector intVector = + new IntVector("to_be_consumed_by_python", allocator); + + public static BufferAllocator getAllocatorForJavaConsumers() { + return allocator; + } + + public static IntVector getIntVectorForJavaConsumers() { + intVector.allocateNew(3); + intVector.set(0, 1); + intVector.set(1, 7); + intVector.set(2, 93); + intVector.setValueCount(3); + return intVector; + } + + public static void closeAllocatorForJavaConsumers() { + try { + AutoCloseables.close(AutoCloseables.iter(intVector)); + } catch (Exception e) { + throw new RuntimeException(e); + } + } + + public static void simulateAsAJavaConsumers() { + try ( + ArrowArray arrowArray = ArrowArray.allocateNew(allocator); + ArrowSchema arrowSchema = ArrowSchema.allocateNew(allocator) + ) { + Data.exportVector(allocator, getIntVectorForJavaConsumers(), null, arrowArray, arrowSchema); + try (FieldVector valueVectors = Data.importVector(allocator, arrowArray, arrowSchema, null);) { + System.out.print(valueVectors); + } + } + closeAllocatorForJavaConsumers(); + allocator.close(); + } + } + + ShareValueVectorAPI.simulateAsAJavaConsumers(); + +.. testoutput:: + + [1, 7, 93] + +Python Side: + +.. code-block:: python + + import jpype + import pyarrow as pa + from pyarrow.cffi import ffi + + jvmargs=["-Darrow.memory.debug.allocator=true"] + jpype.startJVM(*jvmargs, jvmpath=jpype.getDefaultJVMPath(), classpath=[ + "./target/java-python-by-cdata-1.0-SNAPSHOT-jar-with-dependencies.jar"]) + java_value_vector_api = jpype.JClass('ShareValueVectorAPI') + java_c_package = jpype.JPackage("org").apache.arrow.c + py_c_schema = ffi.new("struct ArrowSchema*") + py_ptr_schema = int(ffi.cast("uintptr_t", py_c_schema)) + py_c_array = ffi.new("struct ArrowArray*") + py_ptr_array = int(ffi.cast("uintptr_t", py_c_array)) + java_wrapped_schema = java_c_package.ArrowSchema.wrap(py_ptr_schema) + java_wrapped_array = java_c_package.ArrowArray.wrap(py_ptr_array) + java_c_package.Data.exportVector( + java_value_vector_api.getAllocatorForJavaConsumers(), + java_value_vector_api.getIntVectorForJavaConsumers(), + None, + java_wrapped_array, + java_wrapped_schema + ) + py_array = pa.Array._import_from_c(py_ptr_array, py_ptr_schema) + print(type(py_array)) + print(py_array) + +.. code-block:: shell + + <class 'pyarrow.lib.Int32Array'> + [ + 1, + 7, + 93 + ] + +Sharing VectorSchemaRoot +************************ + +Java Side: + +.. testcode:: + + import org.apache.arrow.c.ArrowArray; + import org.apache.arrow.c.ArrowSchema; + import org.apache.arrow.c.Data; + import org.apache.arrow.memory.BufferAllocator; + import org.apache.arrow.memory.RootAllocator; + import org.apache.arrow.util.AutoCloseables; + import org.apache.arrow.vector.IntVector; + import org.apache.arrow.vector.VectorSchemaRoot; + import org.apache.arrow.vector.types.pojo.ArrowType; + import org.apache.arrow.vector.types.pojo.Field; + import org.apache.arrow.vector.types.pojo.FieldType; + import org.apache.arrow.vector.types.pojo.Schema; + + import static java.util.Arrays.asList; + + public class ShareVectorSchemaRootAPI { + final static BufferAllocator allocator = new RootAllocator(); + final static Field column_one = new Field("column-one", FieldType.nullable(new ArrowType.Int(32, true)), null); + final static Schema schema = new Schema(asList(column_one)); + final static VectorSchemaRoot root = VectorSchemaRoot.create(schema, allocator); + + public static BufferAllocator getAllocatorForJavaConsumers() { + return allocator; + } + + public static VectorSchemaRoot getVectorSchemaRootForJavaConsumers() { + IntVector intVector = (IntVector) root.getVector(0); + root.allocateNew(); + intVector.set(0, 100); + intVector.set(1, 20); + root.setRowCount(2); + return root; + } + + public static void closeAllocatorForJavaConsumers() { + try { + AutoCloseables.close(AutoCloseables.iter(root)); + } catch (Exception e) { + throw new RuntimeException(e); + } + } + + public static void simulateAsAJavaConsumers() { + try (ArrowArray arrowArray = ArrowArray.allocateNew(allocator); + ArrowSchema arrowSchema = ArrowSchema.allocateNew(allocator) + ) { + Data.exportVectorSchemaRoot(allocator, getVectorSchemaRootForJavaConsumers(), null, arrowArray, arrowSchema); + try (VectorSchemaRoot root = Data.importVectorSchemaRoot(allocator, arrowArray, arrowSchema, null);) { + System.out.print(root.contentToTSVString()); + } + } + closeAllocatorForJavaConsumers(); + allocator.close(); + } + } + + ShareVectorSchemaRootAPI.simulateAsAJavaConsumers(); + +.. testoutput:: + + column-one + 100 + 20 + +Python Side: + +.. code-block:: python + + import jpype + import pyarrow as pa + from pyarrow.cffi import ffi + + jvmargs=["-Darrow.memory.debug.allocator=true"] + jpype.startJVM(*jvmargs, jvmpath=jpype.getDefaultJVMPath(), classpath=[ + "./target/java-python-by-cdata-1.0-SNAPSHOT-jar-with-dependencies.jar"]) Review Comment: It would be nice to leave a comment regarding the jar we have mentioned here. -- This is an automated message from the Apache Git Service. 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