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PLDI 2020
Mon 15 - Fri 19 June 2020
Thu 18 Jun 2020 05:00 - 05:20 at PLDI Research Papers live stream - Concurrency Chair(s): Tyler Sorensen

Modern JavaScript includes the SharedArrayBuffer feature, which provides access to true shared memory concurrency. SharedArrayBuffers are simple linear buffers of bytes, and the JavaScript specification defines an axiomatic relaxed memory model to describe their behaviour. While this model is heavily based on the C/C++11 model, it diverges in some key areas. JavaScript chooses to give a well-defined semantics to data-races, unlike the "undefined behaviour" of C/C++11. Moreover, the JavaScript model is mixed-size. This means that its accesses are not to discrete locations, but to (possibly overlapping) ranges of bytes.

We show that the model, in violation of the design intention, does not support a compilation scheme to ARMv8 which is used in practice. We propose a correction, which also incorporates a previously proposed fix for a failure of the model to provide Sequential Consistency of Data-Race-Free programs (SC-DRF), an important correctness condition. We use model checking, in Alloy, to generate small counter-examples for these deficiencies, and investigate our correction. To accomplish this, we also develop a mixed-size extension to the existing ARMv8 axiomatic model.

Guided by our Alloy experimentation, we mechanise (in Coq) the JavaScript model (corrected and uncorrected), our ARMv8 model, and, for the corrected JavaScript model, a "model-internal" SC-DRF proof and a compilation scheme correctness proof to ARMv8. In addition, we investigate a non-mixed-size subset of the corrected JavaScript model, and give proofs of compilation correctness for this subset to x86-TSO, Power, RISC-V, ARMv7, and (again) ARMv8, via the Intermediate Memory Model (IMM).

As a result of our work, the JavaScript standards body (ECMA TC39) will include fixes for both issues in an upcoming edition of the specification.

Thu 18 Jun
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05:00 - 06:00: Concurrency PLDI Research Papers at PLDI Research Papers live stream
Chair(s): Tyler SorensenImperial College London

YouTube lightning session video

05:00 - 05:20
PLDI Research Papers
Conrad WattUniversity of Cambridge, UK, Christopher PulteUniversity of Cambridge, UK, Anton PodkopaevMPI-SWS, NRU HSE, JetBrains Research, Guillaume BarbierENS Rennes, France, Stephen DolanUniversity of Cambridge, UK, Shaked FlurGoogle, Jean Pichon-PharabodUniversity of Cambridge, UK, Shu-yu GuoBloomberg, USA
05:20 - 05:40
PLDI Research Papers
Sung-Hwan LeeSeoul National University, South Korea, Minki ChoSeoul National University, South Korea, Anton PodkopaevMPI-SWS, NRU HSE, JetBrains Research, Soham ChakrabortyIIT Delhi, India, Chung-Kil HurSeoul National University, South Korea, Ori LahavTel Aviv University, Israel, Viktor VafeiadisMPI-SWS, Germany
05:40 - 06:00
PLDI Research Papers
Michal FriedmanTechnion, Israel, Naama Ben-DavidCarnegie Mellon University, USA, Yuanhao WeiCarnegie Mellon University, USA, Guy E. BlellochCarnegie Mellon University, USA, Erez PetrankTechnion, Israel