research-article

Optimized strings for the Java HotSpot™ virtual machine

Authors:

Christian Häubl,

Christian Wimmer,

Hanspeter MössenböckAuthors Info & Claims

PPPJ '08: Proceedings of the 6th international symposium on Principles and practice of programming in Java

Pages 105 - 114

https://doi.org/10.1145/1411732.1411747

Published: 09 September 2008 Publication History

Abstract

In several Java VMs, strings consist of two separate objects: metadata like the string length are stored in the actual string object, while the string characters are stored in a character array. This separation causes an unnecessary overhead. Each string method must access both objects, which leads to a bad cache behavior and reduces the execution speed.

We propose to merge the character array with the string's metadata object at run time. This results in a new layout of strings with better cache performance, fewer field accesses, and less memory overhead. We implemented this optimization for Sun Microsystems' Java HotSpot™ VM, so that the optimization is performed automatically at run time and requires no actions on the part of the programmer. The original class String is transformed into the optimized version and the bytecodes of all methods that allocate string objects are rewritten. All these transformations are performed by the Java HotSpot™ VM when a class is loaded. Therefore, the time overhead of the transformations is negligible.

Benchmarks show a reduction of the average used memory after a full garbage collection and an improved performance. The performance of the SPECjbb2005 benchmark increases by 8%, and the average used memory after a full garbage collection is reduced by 19%. The peak performance of SPECjvm98 is improved by 8% on average, with a maximum speedup of 62%.

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Cited By

Bruno RJovanovic VWimmer CAlonso GFreund SYahav E(2021)Compiler-assisted object inlining with value fieldsProceedings of the 42nd ACM SIGPLAN International Conference on Programming Language Design and Implementation10.1145/3453483.3454034(128-141)Online publication date: 19-Jun-2021
https://dl.acm.org/doi/10.1145/3453483.3454034

Index Terms

Optimized strings for the Java HotSpot™ virtual machine
1. Software and its engineering
  1. Software notations and tools
    1. Compilers
      1. Source code generation

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Published In

cover image ACM Conferences

PPPJ '08: Proceedings of the 6th international symposium on Principles and practice of programming in Java

September 2008

198 pages

ISBN:9781605582238

DOI:10.1145/1411732

Conference Chairs:
Luis Veiga
Universidade Técnica de Lisboa, Portugal
,
Vasco Amaral
Universidade Nova de Lisboa, Portugal

Copyright © 2008 ACM.

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New York, NY, United States

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Published: 09 September 2008

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PPPJ08: Principles and Practice of Prgramming in Java 2008

September 9 - 11, 2008

Modena, Italy

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Cited By

Bruno RJovanovic VWimmer CAlonso GFreund SYahav E(2021)Compiler-assisted object inlining with value fieldsProceedings of the 42nd ACM SIGPLAN International Conference on Programming Language Design and Implementation10.1145/3453483.3454034(128-141)Online publication date: 19-Jun-2021
https://dl.acm.org/doi/10.1145/3453483.3454034

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