This blog post details the author's successful experiment running Clojure code in a web browser using WebAssembly (WASM) compiled via GraalVM Native Image. The process involves using SCI, the self-hosted Clojure interpreter, to create a native image ahead-of-time (AOT) that can be further compiled to WASM. The post highlights several key steps, including preparing a minimal Clojure project, utilizing GraalVM's native-image tool with necessary configuration for WASM, and finally embedding the resulting WASM file in a simple HTML page for browser execution. The author showcases a basic "Hello, World!" example and briefly touches on potential benefits like performance improvements, albeit acknowledging the current limitations and experimental nature of the approach.
Roman Liutikov's blog post, "Running Clojure in WASM with GraalVM," details the process and considerations involved in compiling Clojure code into WebAssembly (WASM) using GraalVM Native Image. The primary motivation is to leverage WASM's portability and performance benefits for running Clojure applications in web browsers and other WASM-compatible environments.
The post begins by acknowledging existing tools like clj-kondo and babashka for compiling ClojureScript, a dialect of Clojure designed for JavaScript interoperability, to WASM. However, it emphasizes the desire to compile Clojure directly, without resorting to ClojureScript. This is where GraalVM Native Image enters the picture.
Liutikov explains that GraalVM's ability to compile Java applications ahead-of-time (AOT) extends to other JVM languages like Clojure. This AOT compilation produces a native executable, which can then be further processed into a WASM binary. The blog post outlines a specific workflow involving several key steps:
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Preparing a simple Clojure project: This involves creating a basic deps.edn file to manage project dependencies, including the org.clojure/clojure dependency itself. A straightforward Clojure function, greet, is defined for demonstration.
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Utilizing the native-image tool: GraalVM's native-image tool is the core component for AOT compilation. The post highlights the importance of including the --language:clojure flag to enable Clojure support and specifies the entry point using --main. Crucially, the --wasm flag instructs the compiler to generate a WASM output instead of a native executable.
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Handling Clojure's runtime dependencies: A significant challenge is ensuring all necessary Clojure runtime libraries are included in the WASM binary. The blog post addresses this by adding a reflect-config.json file which lists classes requiring reflection during runtime. This file is then passed to native-image using the -H:ReflectionConfigurationFiles option.
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Executing the WASM binary: Once the compilation process is complete, the resulting WASM file can be executed within a WASM runtime environment like wasmtime. The post showcases a basic example of running the compiled greet function using wasmtime.
Liutikov further discusses some of the complexities and nuances encountered during the process. Specifically, the post details the challenges of managing Clojure's dynamic nature and reliance on reflection within the context of AOT compilation. The reflect-config.json file becomes crucial for mitigating these challenges by explicitly specifying classes that need reflection support.
The post concludes by acknowledging the experimental nature of compiling Clojure directly to WASM with GraalVM and highlighting the potential for future advancements in this area. The successful execution of a simple Clojure function demonstrates the feasibility of this approach, paving the way for exploring more complex Clojure applications in WASM environments. The author expresses optimism about the potential for improved performance and portability for Clojure applications using this technique.
Summary of Comments ( 29 )
https://news.ycombinator.com/item?id=43810211
Hacker News users discussed the challenges and potential benefits of running Clojure in WASM using GraalVM. Several commenters pointed out the substantial resulting file sizes, questioning the practicality for web applications. Performance concerns were also raised, particularly regarding startup time. Some suggested exploring alternative approaches like using smaller ClojureScript compilers or different WASM runtimes. Others expressed excitement about the possibilities, mentioning potential applications in serverless functions and plugin systems. One commenter highlighted the contrast between the "write once, run anywhere" promise of Java (which GraalVM leverages) and the current state of browser compatibility issues. The overall sentiment leaned towards cautious optimism, acknowledging the technical hurdles while recognizing the potential of Clojure in the WASM ecosystem.
The Hacker News post "Running Clojure in WASM with GraalVM" (https://news.ycombinator.com/item?id=43810211) has several comments discussing the challenges and potential of compiling Clojure to WebAssembly (Wasm).
One commenter highlights the inherent difficulties in making Clojure, a language heavily reliant on the Java Virtual Machine (JVM), work efficiently in a Wasm environment. They point out that the JVM's dynamic nature and garbage collection present significant obstacles to achieving optimal performance in a browser context. This leads to concerns about larger Wasm output sizes compared to other languages better suited for Wasm compilation, like Rust.
The discussion delves into potential solutions and workarounds for these challenges. The use of GraalVM Native Image is mentioned as a way to ahead-of-time compile Java code, potentially reducing the runtime overhead associated with the JVM. However, the effectiveness of this approach with Clojure's dynamic features is questioned. Another commenter mentions that fully leveraging GraalVM Native Image with Clojure requires carefully considering and potentially restricting certain aspects of the language's dynamism.
There's also a comment about the practicalities of debugging Clojure running in Wasm, suggesting it's a more complex process than debugging JavaScript. This contributes to the overall theme of the challenges involved in bridging the gap between Clojure's JVM-centric design and the Wasm environment.
Further discussion involves the limitations of running mutable data structures in a multi-threaded context within Wasm. While Wasm offers threading capabilities, the intricacies of shared memory management and the avoidance of data races become important considerations when porting languages like Clojure that typically handle these complexities within the JVM.
Finally, there's speculation about the future of Wasm and its potential to evolve into a more robust platform capable of efficiently hosting languages like Clojure. This touches upon the hope that advancements in Wasm technology might eventually alleviate the currently identified challenges.