A low Overhead Per Object Write Barrier for the Cog VM

Clément Bera (1)

1 RMOD - Analyses and Languages Constructs for Object-Oriented Application Evolution

In several Smalltalk implementations, a program can mark any object as read-only (unfortunately incorrectly sometimes miscalled immutable). Such read-only objects cannot be mutated unless the program explicitly revert them to a writable state. This feature, called write barrier, may induce noticeable overhead if not implemented carefully, both in memory footprint and execution time. In this paper I discuss the recent addition of the write barrier in the Cog virtual machine and the support introduced in the Pharo 6 image. I detail specific aspects of the implementation that allows, according to multiple evaluations presented in the paper, to have such a feature with little to no overhead.

Mots clés: Store Check; Language Virtual Machine; Just-in-Time Com-pilation; Interpreter; Write Barrier

Domaines: Langage de programmation [cs.PL]

Clément Bera. A low Overhead Per Object Write Barrier for the Cog VM. IWST 16, 2016, Pragues, Czech Republic. ⟨10.1145/2991041.2991063⟩. ⟨hal-01356338⟩