Modernize emscripten usage ("env" "pthread_self": function import requires a callable)

[PeterZhizhin]

If I recompile with a new emscripten compiler version (3.1.64), I get the following error on importing the WebAssembly module:

LinkError: WebAssembly.instantiate(): Import #0 "env" "pthread_self": function import requires a callable
    at 0026ddb4-d116-4418-b697-5ee71eb6c206:157:36
(anonymous) @ 0026ddb4-d116-4418-b697-5ee71eb6c206:157
Promise.then
self.onmessage @ 0026ddb4-d116-4418-b697-5ee71eb6c206:159

The reason for this is that a more recent emscripten (less than ~3 years old) compiler exports additional symbols that we are not defining when calling instantiate.

When compiling as a regular module, emscripten will generate additional JS output file that actually loads all functions:

em++ -std=c++11 sorter.cpp -o sorter.js -s WASM=1 -s USE_PTHREADS=1 -msimd128

This generates the following files:

sorter.js
sorter.wasm

The sorter.js file will actually load the sorter.wasm file into a Module variable. This variable can then be used to access defined C++ functions.

This approach will be more future-proof, since the generated .js file will be different depending on the compiler version.

I'd like to know if something like this was considered. And if it wasn't used, then why.

[mkkellogg]

I admit that I don't have a great reason for the way it is currently implemented other than it's simple and it works :) When I originally implemented it, I basically got a quick & dirty solution working and never bothered to change how the web worker or WASM module were set up after that. For what it's worth, I can compile and import just fine using emscripten 3.1.6, which was release in May of this year. I'm using the following command:

em++ -std=c++11 sorter.cpp -Os -s WASM=1 -s SIDE_MODULE=2 -o sorter.wasm -s IMPORTED_MEMORY=1 -s USE_PTHREADS=1 -msimd128

[JiamingSuen]

I'm having the same problem. I cannot reproduce the compiled sorter.wasm file in the repo with emscripten version 3.1.60 (on both macOS and Linux). The compiled wasm also produces Import #0 "env" "pthread_self": function import requires a callable error, same as 3.1.64. @mkkellogg Could you tell me which version of emscripten should be used to compile a usable wasm file? Thanks very much!

[mkkellogg]

@JiamingSuen I am also using version 3.1.6, and I am using the command below to compile it:

em++ -std=c++11 sorter.cpp -Os -s WASM=1 -s SIDE_MODULE=2 -o sorter.wasm -s IMPORTED_MEMORY=1 -s USE_PTHREADS=1 -msimd128

Can you try that command on your machine?

[JiamingSuen]

@JiamingSuen I am also using version 3.1.6, and I am using the command below to compile it:

em++ -std=c++11 sorter.cpp -Os -s WASM=1 -s SIDE_MODULE=2 -o sorter.wasm -s IMPORTED_MEMORY=1 -s USE_PTHREADS=1 -msimd128

Can you try that command on your machine?

I tried this command with Emscripten 3.1.60 on the current HEAD, and although I didn't modify sorter.cpp, the sorter.wasm file was updated. As a result, the webpage fails to load properly, showing the error "env" "pthread_self": function import requires a callable as the title suggests. This issue occurred after running another npm run build, which was necessary to update the JavaScript code in the build/demo folder.

If our Emscripten version matches, is it possible that the current sorter.wasm in the repo does not match the content of sorter.cpp?

$ em++ --version
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.60 (42a6ea2052f19f70d7d994e8c324bcad2f1f8939)

[JiamingSuen]

I just realized that you are using Emscripten 3.1.6, which is different from 3.1.60😂
3.1.6 was released two years ago.

By switching to 3.1.6, the compiled sorter.wasm is working again.

[mkkellogg]

Ha, good catch! I will look into how I can make it work with a more current version, like 3.1.60.