Copy-on-write in the PHP language

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Copy-on-write in the PHP language

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Annual Symposium on Principles of Programming Languages archive
Proceedings of the 36th annual ACM SIGPLAN-SIGACT symposium on Principles of programming languages table of contents

Savannah, GA, USA

SESSION: Medley II table of contents

Pages 200-212

Year of Publication: 2009

ISBN:978-1-60558-379-2

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Authors

Akihiko Tozawa	IBM Research, Tokyo Research Laboratory, Tokyo, Japan
Michiaki Tatsubori	IBM Research, Tokyo Research Laboratory, Tokyo, Japan
Tamiya Onodera	IBM Research, Tokyo Research Laboratory, Tokyo, Japan
Yasuhiko Minamide	University of Tsukuba, Tsukuba, Japan

Sponsors

ACM: Association for Computing Machinery
SIGACT: ACM Special Interest Group on Algorithms and Computation Theory
SIGPLAN: ACM Special Interest Group on Programming Languages

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ACM New York, NY, USA

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Downloads (6 Weeks): 41, Downloads (12 Months): 196, Citation Count: 1

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ABSTRACT

PHP is a popular language for server-side applications. In PHP, assignment to variables copies the assigned values, according to its so-called copy-on-assignment semantics. In contrast, a typical PHP implementation uses a copy-on-write scheme to reduce the copy overhead by delaying copies as much as possible. This leads us to ask if the semantics and implementation of PHP coincide, and actually this is not the case in the presence of sharings within values. In this paper, we describe the copy-on-assignment semantics with three possible strategies to copy values containing sharings. The current PHP implementation has inconsistencies with these semantics, caused by its naïve use of copy-on-write. We fix this problem by the novel mostly copy-on-write scheme, making the copy-on-write implementations faithful to the semantics. We prove that our copy-on-write implementations are correct, using bisimulation with the copy-on-assignment semantics.

REFERENCES

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