Threads with WebAssembly

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2025-01-08 11:30:02

Multi-threading is a cornerstone of modern programming, enabling applications to handle multiple tasks simultaneously. While web browsers support concurrency through the Web Workers API, WebAssembly (Wasm) still lacks built-in thread support. Currently, threading in Wasm is part of an active proposal in Phase 4 (standardizing the feature), as detailed in the WebAssembly specification.

We faced this challenge while developing our proof of concept, TonboLite. TonboLite is a WASM compatible SQLite extension written in Rust that allows users to create tables which supports analytical processing directly in SQLite. Its storage engine is powered by our open-source embedded key-value database, Tonbo. While Tonbo is thread-safe and supports asynchronous I/O, SQLite does not. When Tonbo operates as an extension within SQLite on the same thread, SQLite blocks Tonbo from scheduling asynchronous I/O, undermining the advantages of thread safety and asynchronous operations. To address this, we aimed to enable multiple SQLite threads to access a single Tonbo instance in parallel.

In this article, we will explore the current landscape of multi-threading in Wasm. Using Rust as our primary example, we'll demonstrate how to leverage multi-threading in Wasm at the moment—a technique that is theoretically applicable to other programming languages compiled to Wasm as well.