Persistent Collections for Java*
This is a "pilot" project to develop a library for Java objects stored in persistent memory. Persistent collections are being emphasized because many applications for persistent memory seem to map well to the use of collections. One of this project's goals is to make programming with persistent objects feel natural to a Java developer, for example, by using familiar Java constructs when incorporating persistence elements such as data consistency and object lifetime.
The breadth of persistent types is currently limited and the code is not performance-optimized. We are making the code available because we believe it can be useful in experiments to retrofit existing Java code to use persistent memory and to explore persistent Java programming in general.
This library provides Java classes whose instances can persist (i.e. remain reachable) beyond the life of a Java VM instance. Persistent classes include:
- Primitive arrays
- Generic arrays
- Boxed primitives
For a brief introduction on use of the library, please see Introduction.txt.
HOW TO BUILD & RUN
PREREQUISITES TO BUILD
The following are the prerequisites for building this Java library:
- Linux operating system (tested on CentOS 7.2 and Ubuntu 16.04)
- Persistent Memory Development Kit (PMDK)
- Java 8 or above
- Build tools - g++ compiler and make
PREREQUISITES TO RUN
This library assumes the availability of hardware persistent memory or emulated persistent memory. Properties of this memory such as path and size can be specified in the config.properties file at the top level directory. Further information can be found inside the file.
Instructions for creating emulated persistent memory are shown below.
EMULATING PERSISTENT MEMORY
The preferred way is to create an in-memory DAX file system. This requires Linux kernel 4.2 or greater. Please follow the steps at:
Alternatively, for use with older kernels, create a tmpfs partition as follows (as root):
$ mount -t tmpfs -o size=4G tmpfs /mnt/mem # creates a 4GB tmpfs partition $ chmod -R a+rw /mnt/mem # enables read/write permissions to all users
STEPS TO BUILD AND RUN TESTS
Once all the prerequisites have been satisfied:
$ git clone https://github.com/pmem/pcj $ cd pcj $ make && make tests
Available Makefile targets include:
sources- builds only sources
examples- builds the sources and examples
tests- builds and runs tests
USING THIS LIBRARY IN EXISTING JAVA APPLICATIONS
To import this library into an existing Java application, include the project's target/classes
directory in your Java classpath and the project's
target/cppbuild directory in your
java.library.path. For example:
$ javac -cp .:<path>/pcj/target/classes <source> $ java -cp .:<path>/pcj/target/classes -Djava.library.path=<path>/pcj/target/cppbuild <class>
NOTES ON FUNCTIONALITY
PersistentStringobjects are backed by a byte array and only supports ASCII characters.
Thanks for your interest! Right now, substantial architectural changes are still happening in the project. This makes it difficult to contribute code and difficult to effectively process pull requests. We expect these changes to settle out around December of this year and we look forward to code contributions once this happens. We will update this README then.
In the meantime, we would love to hear your comments and suggestions via the contacts listed below.
* Other names and brands may be claimed as the property of others.