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DataSketches Java Memory Component

This Memory component is general purpose, has no external runtime dependencies and can be used in any application that needs to manage data structures inside or outside the Java heap.

Please visit the main DataSketches website for more information.

If you are interested in making contributions to this Memory component please see our Community page.

The goal of this component of the DataSketches library is to provide a high performance access API for accessing four different types of memory resources:

• On-heap Memory via primitive arrays
• On-heap Memory via ByteBuffers
• Off-heap (Direct or Native) Memory via direct allocation
• Off-Heap Memory-Mapped files

Each of the four resource types is accessed using different API methods in the Memory component.

Note: primitive := {byte, short, int, long, float, double}

Contiguous bytes on the Java Heap constructed by these examples:

• Heap via primitive arrays:

  • Memory.wrap(primitive[]) (read only)
  • WritableMemory.allocate(int)
  • WritableMemory.writableWrap(primitive[])

• Heap via ByteBuffer

  • Memory.wrap(ByteBuffer.wrap(byte[])) (read only)
  • WritableMemory.writableWrap(ByteBuffer.allocate(int))

Contiguous bytes off the Java Heap constructed by these examples:

• Off-Heap, Direct via direct allocation:

  • WritableMemory.allocateDirect(long)

• Off-Heap, Direct via (Direct) ByteBuffer

  • WritableMemory.writableWrap(ByteBuffer.allocateDirect(int))

• Off-Heap, Memory-Mapped Files

  • Memory.map(File, Arena) (read only)
  • WritableMemory.writableMap(File)

Release 5.0.0 (inclusive) to 7.0.0 (exclusive)

Starting with release datasketches-memory-5.0.0, this Memory component supports only Java 21 when compiling from source and may work with later Java versions at runtime.

Runtime Notes:

• There are no run-time dependencies.
• The DataSketches Java Memory Component is not thread-safe.
• This Release, based on Java 21, leverages the new Java Foreign Function & Memory (FFM) API JEP 442, which is in its third Preview and will require the JVM flag –enable-preview at run-time.
• We recommend Eclipse Adoptium/Temurin 21.0.5+11 or later as earlier releases of 21 have bugs that affect this product.
• This component is not designed as a Java Module, so the Jar file should be part of the application classpath.

Build Instructions

NOTES:

• This component accesses resource files for testing. As a result, the directory elements of the full absolute path of the target installation directory must qualify as Java identifiers. In other words, the directory elements must not have any space characters (or non-Java identifier characters) in any of the path elements. This is required by the Oracle Java Specification in order to ensure location-independent access to resources: See Oracle Location-Independent Access to Resources
• The compile command line must contain the JVM flag –enable-preview (see JEP 442).

Build & Test Dependencies

• There are two direct build dependencies, both of which are only used in test scope:
  • org.testng/testng
  • net.openhft/zero-allocation-hashing
• See the pom.xml file for maven plug-in dependencies.

Maven build instructions

The Maven build requires JDK-21 to compile:

• We recommend Eclipse Adoptium/Temurin 21.0.5+11 or later as earlier releases of 21 have bugs that affect this product.

To run normal unit tests:

mvn clean test

To run javadoc:

mvn clean javadoc:javadoc -DskipTests=true

To run the eclipse plugin on this project, use:

mvn clean eclipse:eclipse -DskipTests=true

To install jars built from the downloaded source:

mvn clean install -DskipTests=true

This will create the following Jars:

• datasketches-memory-X.Y.Z.jar The compiled main class files.
• datasketches-memory-X.Y.Z-tests.jar The compiled test class files.
• datasketches-memory-X.Y.Z-sources.jar The main source files.
• datasketches-memory-X.Y.Z-test-sources.jar The test source files
• datasketches-memory-X.Y.Z-javadoc.jar The compressed Javadocs.

Deployment to Nexus

For releasing to Nexus, please use the sign-deploy-jar.sh script in the scripts directory. See the documentation within the script for usage instructions.