worker.js file should be placed into the output directory when targeting Emscripten with pthread support about cargo HOT 3 OPEN

Thanks for the report!

Could you share some more specifications and documentations of that output behavior of emscripten? I found one here, but not sure if it always does that. worker.js could possibly be considered as an auxiliary file and uplifted for empscripten target, though we might need to understand the stability before moving forward. We might also bump into issues like #13355 and #13358 when dealing with it.

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BTW, are there any more files for emscripten that we want to uplift to the target directory?

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Hi @weihanglo

Thanks for a quick response! In the Special Considerations section it mentions that the worker.js will be always generated when compiling with -pthread flag and the file must be deployed:

Also note that when compiling code that uses pthreads, an additional JavaScript file NAME.worker.js is generated alongside the output .js file (where NAME is the basename of the main file being emitted). That file must be deployed with the rest of the generated code files.

In addition, -pthread is not the only case when Emscripten generates a worker.js. According to the emcc compiler manual , when linking with --proxy-to-worker flag it will also generate worker.js when emitting JavaScript. Cargo always emits JavaScript and never targets HTML when building for wasm32.

--proxy-to-worker
[link] Runs the main application code in a worker, proxying events to it and output from it. If emitting HTML, this emits a .html file, and a separate .js file containing the JavaScript to be run in a worker. If emitting JavaScript, the target file name contains the part to be run on the main thread, while a second .js file with suffix “.worker.js” will contain the worker portion.

Emscripten choses what to emit based on a suffix of the output file: .js for JavaScript and .html for HTML. The following condition in cargo guarantees that Emscripten will emit JavaScript (due to .js suffix) and therefore we get a worker.js file.

Additional files

BTW, are there any more files for emscripten that we want to uplift to the target directory?

Yes indeed. Those files are: .data, .data.js and .mem. See Build Files. data related files are the important ones. They contain preloaded files and directories that will populate the virtual file system. See Packaging Files. It is difficult to envision an app without asset files. Please consider outputting them as well.

Cheers

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