Java for High Performance Computing

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

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Index of the TalkThe 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

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The Java Programming LanguajeFeatures 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

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The Java Programming LanguajeJava 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, ...

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The Java Programming LanguajeJava 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

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The Java Programming LanguajeJava 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

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The Java Runtime SystemJava Virtual Machine: bytecode interpreter

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The Java Runtime SystemStructure of the Java Virtual MachineThe JVM implementation can be tailored for high performance, low memory use, or portability

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The Java Runtime SystemDrawbacks 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

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The Java Runtime SystemJust-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!

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The Java Runtime SystemJava 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!

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The Java Runtime SystemJava 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

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Java for HPCDifferent 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

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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

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Java for HPCJava 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

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Java for HPCParallel 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

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The SurveyAvailable (under construction) at URL: file:/usr/users.coderch/ac/jordig/pub/Java4HPC/main.html

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Last Updated: 8th March 2018

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