This is an example project of how to use threads in C++ with WebAssembly and how to communicate between the C++ and JavaScript worlds with Embind.

See it in action.

Setup

• Install cmake.
• Install and initialize the Emscripten SDK from https://emscripten.org.
• Then:

mandelbrot-wasm # mkdir build
mandelbrot-wasm # cd build
build # emcmake cmake ..
build # make
build # emrun --port 8000 --no_browser .

• Point your browser to http://localhost:8000/www/index.html

Important note to mobile users:

Unfortunately. mobile browsers currently do not support running multi-threaded WebAssembly. Sorry!

Important note to Chrome/Chromium users:

Chrome/Chromium 68 or higher is required.

https://www.chromium.org/Home/chromium-security/ssca

Important note to Edge users:

Edge 79 or higher is required.

https://blogs.windows.com/msedgedev/2018/01/03/speculative-execution-mitigations-microsoft-edge-internet-explorer/

Important note to Firefox users:

TL;DR: It won't run in Firefox right now. Mozilla is working to fix it (since 2018...).

Due to several security enforcements, Firefox is currently (Firefox 77) still unable to run multi-threaded WebAssembly.

• Because of the Spectre vulnerability, Firefox (temporarily?) disabled support for SharedArrayBuffer in 2018. This effectively disables the use of multi-threaded WebAssembly.

  https://blog.mozilla.org/security/2018/01/03/mitigations-landing-new-class-timing-attack/

  It can be enabled (with the risk of Spectre vulnerability) in about:config:

  javascript.options.shared_memory = true
  

  Enable at your own risk.

• Further enforcement are in place, too, making life hard.

  emscripten-core/emscripten#10014

• You might have a better chance of running this code in Firefox Nightly.

  • https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer/Planned_changes

  • https://bugzilla.mozilla.org/show_bug.cgi?id=1619649