WebAssembly is designed to be an alternative to JavaScript that is a safe, portable, and efficient compilation target for a variety of languages. The performance of high-level languages depends not only on the underlying performance of WebAssembly, but also on the quality of the generated WebAssembly code. In this paper, we identify several features of high-level languages that current approaches can only compile to WebAssembly by generating complex and inefficient code. We argue that these problems could be addressed if WebAssembly natively supported first-class continuations. We then present Wasm/k, which extends WebAssembly with delimited continuations. Wasm/k introduces no new value types, and thus does not require significant changes to the WebAssembly type system (validation). Wasm/k is safe, even in the presence of foreign function calls (e.g., to and from JavaScript). Finally, Wasm/k is amenable to efficient implementation: we implement Wasm/k as a local change to Wasmtime, an existing WebAssembly JIT. We evaluate Wasm/k by implementing C/k, which adds delimited continuations to C/C++. C/k uses Emscripten and its implementation serves as a case study on how to use Wasm/k in a compiler that targets WebAssembly. We present several case studies using C/k, and show that on implementing green threads, it can outperform the state-of-the-art approach Asyncify with an 18% improvement in performance and a 30% improvement in code size.
@inproceedings{Pinckney20dls,
author = {Donald Pinckney and Arjun Guha and Yuriy Brun},
title =
{Wasm/k: {Delimited} Continuations for WebAssembly},
booktitle = {Proceedings of the ACM SIGPLAN International Symposium on Dynamic Languages (DLS)},
venue = {DLS},
address = {Chicago, IL, USA},
month = {November},
date = {15--20},
year = {2020},
pages = {16--28},
doi = {10.1145/3426422.3426978},
note = {DOI: 10.1145/3426422.3426978,
arXiv: abs/1902.05870},
accept = {$\frac{9}{14} \approx 64\%$},
fundedBy = {CCF-2007066, CCF-1453474, CCF-1564162},
abstract = {WebAssembly is designed to be an alternative to JavaScript that is a safe,
portable, and efficient compilation target for a variety of languages. The
performance of high-level languages depends not only on the underlying
performance of WebAssembly, but also on the quality of the generated
WebAssembly code. In this paper, we identify several features of high-level
languages that current approaches can only compile to WebAssembly by
generating complex and inefficient code. We argue that these problems could
be addressed if WebAssembly natively supported first-class continuations. We
then present Wasm/k, which extends WebAssembly with delimited continuations.
Wasm/k introduces no new value types, and thus does not require significant
changes to the WebAssembly type system (validation). Wasm/k is safe, even in
the presence of foreign function calls (e.g., to and from JavaScript).
Finally, Wasm/k is amenable to efficient implementation: we implement Wasm/k
as a local change to Wasmtime, an existing WebAssembly JIT. We evaluate
Wasm/k by implementing C/k, which adds delimited continuations to C/C++. C/k
uses Emscripten and its implementation serves as a case study on how to use
Wasm/k in a compiler that targets WebAssembly. We present several case
studies using C/k, and show that on implementing green threads, it can
outperform the state-of-the-art approach Asyncify with an 18% improvement in
performance and a 30% improvement in code size.},
}