Nowadays, almost everyone interested in parallel and distributed calculations pays a lot of attention to the development of the hardware. However, changes in hardware are associated with changes in the programming languages. A good example is Java with its increasing performance and parallelization tools introduced in Java SE 5 and improved in Java SE 6. Java, from the beginning, put emphasis on parallel execution introducing as far back as in the JDK1.0 the Thread class. The parallelization tools available for Java include solutions based on various implementations of the MPI library, distributed Java Virtual Machine and solutions based on Remote Method Invocation (RMI).

PCJ is a library for Java language that helps to perform parallel and distributed calculations. The current version is able to work on the multicore systems connected with the typical interconnect such as ethernet or infiniband providing users with the uniform view across nodes.

The library implements partitioned global address space model and was inspired by languages like Co-Array Fortran [8], Unified Parallel C and Titanium. In contrast to listed languages, the PCJ does not extend nor modify language syntax. For example, Titanium is a scientific computing dialect of Java, defines new language constructs and has to use dedicated compiler. When developing the PCJ library, we put emphasis on compliance with Java standards. The programmer does not have to use additional libraries, which are not part of the standard Java distribution. Compared to the Titanium, PCJ does not need a dedicated compiler to preprocess code.

The first prototype version of PCJ has been developed from scratch using the Java SE 7. Java SE 7 implements Sockets Direct Protocol (SDP), which can increase network performance over infiniband connections. Than the internode communication has been added allowing users to run multiple PCJ threads withon single Java Virtual Machine. Next stable version has been developed in 2013 and includes many bug fixes and improvements compare to the initial version. Especially the users interface has been stabilized. Current version has been developed in 2019 and includes performance improvements as well as changes in the API to make programming easier.

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