Dynamic Web Sample

This experimental sample demonstrates one way to target the web platform with IREE. The output artifact is a web page that loads separately provided IREE .vmfb (compiled ML model) files and allows for calling functions on them.

Quickstart

  1. Install IREE's host tools (e.g. by building the install target with CMake)
  2. Install the Emscripten SDK by following these directions
  3. Initialize your Emscripten environment (e.g. run emsdk_env.bat)
  4. From this directory, run bash ./build_sample.sh [path to install] && bash ./serve_sample.sh
  5. Open the localhost address linked in the script output

To rebuild most parts of the sample (C runtime, sample HTML, CMake config, etc.), just control + C to stop the local webserver and rerun the script.

How it works

Emscripten is used (via the emcmake CMake wrapper) to compile the runtime into WebAssembly and JavaScript files.

Any supported IREE program, such as simple_abs.mlir, is compiled using the “system library” linking mode. This creates a shared object (typically .so/.dll, .wasm in this case). When the runtime attempts to load this file using dlopen() and dlsym(), Emscripten makes use of its runtime dynamic linking support to instantiate a new WebAssembly.Instance which shares memory with the main runtime then resolve each export provided by the new Wasm module.

Asynchronous API

  • iree_api.js exposes a Promise-based API to the hosting application in index.html
  • iree_api.js creates a worker running iree_worker.js, which includes Emscripten's JS code and instantiates the WebAssembly module
  • messages are passed back and forth between iree_api.js and iree_worker.js internally

Multithreading

Multithreading is not supported yet. Emscripten only has experimental support for dynamic linking + pthreads: https://emscripten.org/docs/compiling/Dynamic-Linking.html#pthreads-support. Compiled programs produced by IREE link with wasm-ld, while Emscripten expects programs to be linked using emcc with the -s SIDE_MODULE option, which includes several Emscripten-pthreads-specific module exported functions such as emscripten_tls_init.