Garbage Collection and Eciency in Dynamic Metacircular Runtimes

In dynamic object-oriented languages, low-level mechanisms such as just-in-time compilation, object allocation, garbage collection (GC) and method dispatch are o‰en handled by virtual machines (VMs). VMs are typically implemented using static languages, allowing only few changes at run time. In such systems, the VM is not part of the language and interfaces to memory management or method dispatch are €xed, not allowing for arbitrary adaptation. Furthermore, the implementation can typically not be inspected or debugged with standard tools used to work on application code. Œis paper reports on our experience building Bee, a dynamic Smalltalk runtime, wriŠen in Smalltalk. Bee is a Dynamic Metacircular Runtime (DMR) and seamlessly integrates the VM into the application and thereby overcomes many restrictions of classic VMs, for instance by allowing arbitrary code modi€cations of the VM at run time. Furthermore, the approach enables developers to use their standard tools for application code also for the VM, allowing them to inspect, debug, understand, and modify a DMR seamlessly. We detail our experience of implementing GC, compilation, and optimizations in a DMR. We discuss examples where we found that DMRs can improve understanding of the system, provide tighter control of the so‰ware stack, and facilitate research. We also show that in high-level benchmarks the Bee DMR performance is close to that of a widely used Smalltalk VM. CCSConcepts •So…ware and its engineering→Object oriented languages; Runtime environments; Garbage collection; Dynamic compilers; DLS’17, Vancouver, Canada © 2017 Copyright held by the owner/author(s). Publication rights licensed to ACM. Œis is the author’s version of the work. It is posted here for your personal use. Not for redistribution. Œe de€nitive Version of Record was published in Proceedings of 13th ACM SIGPLAN International Symposium on Dynamic Languages, October 25–27, 2017 , h‚p://dx.doi.org/10.1145/3133841. 3133845.