To leverage the benefits of modern hardware, dynamic languages must support parallelism, and parallelism requires a virtual machine (VM) capable of parallel execution — a parallel VM. However, unrestricted concurrency and the dynamism of dynamic languages pose great challenges to the implementation of parallel VMs. In a dynamic language, a program changing itself is part of the language model. To help the VM, languages often choose memory models (MM) that weaken consistency guarantees. With lesser guarantees, local program state cannot be affected by every concurrent state change. And less interference allows a VM to make local assumptions about the program state which are not immediately violated. These local assumptions are essential for a VM’s just-in-time compiler for delivering state-of-the-art VM performance. Unfortunately, some dynamic languages employ MMs that give exceedingly strong consistency guarantees and thereby hinder the development of parallel VMs. Such is the case in particular for languages that depend on a global interpreter lock, which mandates a MM with sequential consistency and instruction atomicity. In this paper, we reflect on a first implementation of the Parallel RPython execution model, which facilitates the development of parallel VMs by decoupling language semantics from the synchronization mechanism used within the VM. The implementation addresses the challenges imposed by strong MMs through strict isolation of concurrent computations. This isolation builds on transactional parallel worlds, which are implemented with a novel combination of software techniques and the capabilities of modern hardware. We evaluate a set of parallel Python programs on a parallel VM that relies on Parallel RPython’s implementation. Compared with a serial baseline VM that relies on a global interpreter lock, the parallel VM achieves speedups of up to 7.5× on 8 CPU cores. The evaluation shows that our realization of Parallel RPython meets the challenges of dynamic languages, and that it can serve as a solid foundation for the construction of parallel dynamic language VMs.

The RPython framework takes an interpreter for a dynamic language as its input and produces a Virtual Machine (VM) for that language. RPython is being used to develop PyPy, a high-performance Python interpreter. However, the produced VM does not support parallel execution since the framework relies on a Global Interpreter Lock (GIL): PyPy serialises the execution of multi-threaded Python programs.

The performance of many dynamic language implementations suffers from high allocation rates and runtime type checks. This makes dynamic languages less applicable to purely algorithmic problems, despite their growing popularity. In this paper we present a simple compiler optimization based on online partial evaluation to remove object allocations and runtime type checks in the context of a tracing JIT. We evaluate the optimization using a Python VM and find that it gives good results for all our (real-life) benchmarks.

A powerful application of specialization is to remove interpretative overhead: a language can be implemented with an interpreter, whose performance is then improved by specializing it for a given program source. This approach is only moderately successful with very high level languages, where the operation of each single step can be highly dependent on run-time data and context. In the present paper, the Psyco prototype for the Python language is presented. It introduces two novel techniques. The first is just-in-time specialization, or specialization by need, which introduces the "unlifting" ability for a value to be promoted from run-time to compile-time during specialization -- the inverse of the lift operator of partial evaluation. Its presence gives an unusual and powerful perspective on the specialization process. The second technique is representations, a theory of data-oriented specialization generalizing the traditional specialization domains (i.e. the compile-time/run-time dichotomy).