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Java for High Performance Computing

Java for High Performance Computing. Jordi Garcia Almiñana 14 de Octubre de 1998 de la era post-internet. Index of the Talk. The Java Programming Language Java for Scientific Computation Java limitations for Scientific Computation The Java Runtime System

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Java for High Performance Computing

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  1. Java for High Performance Computing Jordi Garcia Almiñana 14 de Octubre de 1998de la era post-internet

  2. Index of the Talk • The Java Programming Language • Java for Scientific Computation • Java limitations for Scientific Computation • The Java Runtime System • The Java Virtual Machine environment • Alternatives to the basic JVM specification • Java for High Performance Computing • Definition of HPC language extensions for Java • Java restructurers, compilers, and optimizers • Parallel systems for High Performance Java

  3. The Java Programming Languaje • Features of Java • Object-Oriented environment • Platform independence • Network support • Security • Runtime environment • Secure remote transactions • Multithreading support • Automatic memory management • Fault tolerance through exception handling Java for High Performance Computing

  4. The Java Programming Languaje • Java for Scientific Computation • OO programming is preferable for design and maintainability • Data type safety • Automatic memory management (garbage collection) • Java arithmetic is fully protable(in other languages, loss of precission in float temporary expressions can give different results) • Truly portable threads and synchronization model • Portable libraries for distributed programming • GUI, programmer force, availability, ... Java for High Performance Computing

  5. The Java Programming Languaje • Java Limitations for Scientific Computation • Java´s floating point restricted specification • Limits exploitation of current and future chips architecture • No support to complex numbers • Internal implementation of arrays • Non-consecutive memory layout scheme • Multidimensional arrays implemented as arrays of arrays(no unrolling, loss of locality, …) • Array boundary checking for every single array access • The Java run-time exception mechanism Java for High Performance Computing

  6. The Java Programming Languaje • Java Limitations for Scientific Computation • No support to high degrees of parallelism • Parallel programming only through threads mechanism • No facility for explicit locality management • Other compiler related issues • Unavailability of the complete program at compile time • The exception mechanism limits code movement • High level abstraction of JVM instruction set hides many machine dependent optimization opportunities Java for High Performance Computing

  7. file.java - Java source code application javac - Java to bytecode translation (performed only once) file.class - Java bytecode class file (JVM instruction set) Network? Java virtualmachine - Java Virtual Machine Specification - format of class files - semantics of instructions The Java Runtime System • Java Virtual Machine: bytecode interpreter Java for High Performance Computing

  8. java virtual machine file.class garbagecollectedheap dynamic class loader standardclasses class verifier operatingsystem executionengine native method linker nativemethods The Java Runtime System • Structure of the Java Virtual Machine • The JVM implementation can be tailored for high performance, low memory use, or portability Java for High Performance Computing

  9. The Java Runtime System • Drawbacks of JVM: Speed! • Java bytecode is interpreted • Bytecode verification rules and exception mechanism • High-level structure about original program is lost • Local view during invocation of classes • Stack-based operands (no registers) • Alternatives: • Just-in-time code generation • Java static compilation to native code • Java OS and Java Processors Java for High Performance Computing

  10. The Java Runtime System • Just-in-time Code Generation • Java bytecode to native object code on-the-fly • Just before the method is run for the first time • Based on the idea of inlining the machine code • Certain optimizations can be performed • Elimination of redundant instructions • Use hardware registers for local variables • Optimization of method stack usage • However compilation speed requirements constrain the quality of the optimizations • Improvements over interpretation by a factor of 10! Java for High Performance Computing

  11. The Java Runtime System • Java Static Compilation to Native Code • Traditional resource-intensive optimization techniques can improve the performance of the generated code • instruction schedulling • common subexpression elimination • inter-module analysis • constant propagation • global register allocation • Run time checking can be optimized or removed • …but portability and security can be lost! Java for High Performance Computing

  12. The Java Runtime System • Java OS • Java applications run directly on hardware platforms without requiring a host OS • Java Processors • Hardware implementation of a Java interpreter • Chips created specifically to run Java bytecode • Sun implementations: picoJava, microJava Java for High Performance Computing

  13. file.java javac file.class Java virtualmachine Java for HPC • Different levels of research - Language extension - Mathematical libraries - Restructuring compiler - Bytecode optimization - JIT optimization techniques - Runtime parallel kernel library - Parallel Java Virtual Machine - Hardware Java implementations Java for High Performance Computing

  14. Java for HPC • HPC Language Extensions for Java • Language extension • multidimensional arrays • data parallel distributed loops • communication primitives • Java numerical (matrix-oriented) libraries • Floating-point precission and complex numbers • Other Java Dialects • Titanium: language and system for parallelism • Spar: semi-automatic parallel compilation Java for High Performance Computing

  15. Java for HPC • Java Restructurers • Source-to-source tools that extract parallelism(implicitly from loops or explicitly from annotations) • Java Compilers • Java to parallel bytecode translation • Definition of IR for parallel optimization • Bytecode Optimizers • Techniques for automatic detection of parallelism • Machine-dependent optimizations • Just-in-time optimizations Java for High Performance Computing

  16. Java for HPC • Parallel Systems for HPC in Java • Parallel implementation of a JVM • Programming based on SPMD Java • Based on PVM or MPI implementations • Environment definition for network parallel programs • Heterogeneous environment(run-time systems or parallel libraries) • Parallel sparse computation in Java • Runtime environment with continuous compilation Java for High Performance Computing

  17. The Survey • Available (under construction) at URL: file:/usr/users.coderch/ac/jordig/pub/Java4HPC/main.html Java for High Performance Computing

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