built OpenCV.js fails to load wasm in node.js

[peteruhnak]

System information (version)

• OpenCV => 4.5.1 & master
• Operating System / Platform => node 8/10/14 (built on ubuntu 20)
• Compiler => emscripten

Detailed description

Expected behavior:

1. Running opencv.js via node built using the documented instructions correctly loads, passes all tests and runs test_async.js (see further).
   • build instructions https://docs.opencv.org/master/d4/da1/tutorial_js_setup.html
2. Pre-built opencv.js passes all tests and test_async.js
   • distributed opencv.js https://docs.opencv.org/master/opencv.js

Note that running the tests.html via browser works correctly, the failures are specific to running via node.js.

Actual behavior:

1. Self-built opencv.js
   • node tests.js fails to even fail properly and instead just reports 0 failed, 0 passed
   • node test_async.js fails to load wasm due to needing experimental wasm threads & shared memory
     • RuntimeError: abort(RuntimeError: abort(CompileError: WebAssembly.instantiate(): Compiling function #73 failed: Invalid opcode (enable with --experimental-wasm-threads) @+39429)
     • (with threads enabled) RuntimeError: abort(RuntimeError: abort(CompileError: WebAssembly.instantiate(): Compiling function #73 failed: Atomic opcodes used without shared memory @+39428)
2. Pre-built opencv.js
   • node tests.js fails most tests (34 failed, 10 passed), due to improper loading
   • node test_async.js works as expected (and generally using the pre-built library works as expected when loaded properly)
     **

Running node tests.js simply outputs:

Testing  /home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js ... 
0 failed, 0 passed

If I modify tests.js and only allow a single file (e.g. tests: [ 'test_mat.js']) I instead get the following error:

You are getting _malloc on the Promise object, instead of the instance. Use .then() to get called back with the instance, see the MODULARIZE docs in src/settings.js
RuntimeError: abort(You are getting _malloc on the Promise object, instead of the instance. Use .then() to get called back with the instance, see the MODULARIZE docs in src/settings.js) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at Promise.get (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7202)
    at Object.<anonymous> (/home/ubuntu/prog/docker-opencv/js_wasm/bin/test_mat.js:756:26)
    at runTest (/home/ubuntu/prog/docker-opencv/js_wasm/bin/node_modules/node-qunit/node_modules/qunit/qunit/qunit.js:3044:32)
    at Test.run (/home/ubuntu/prog/docker-opencv/js_wasm/bin/node_modules/node-qunit/node_modules/qunit/qunit/qunit.js:3032:8)
    at /home/ubuntu/prog/docker-opencv/js_wasm/bin/node_modules/node-qunit/node_modules/qunit/qunit/qunit.js:3255:15
    at processTaskQueue (/home/ubuntu/prog/docker-opencv/js_wasm/bin/node_modules/node-qunit/node_modules/qunit/qunit/qunit.js:2640:26)
    at /home/ubuntu/prog/docker-opencv/js_wasm/bin/node_modules/node-qunit/node_modules/qunit/qunit/qunit.js:2644:12
0 failed, 0 passed

This is presumably due to the tests not loading the library correctly.

**

Running node test_async.js (code see further) produces the following error:

Node 8/Node 10 -- generic decoding error:

failed to asynchronously prepare wasm: CompileError: WasmCompile: Wasm decoding failed: unexpected section: Code @+37433
CompileError: WasmCompile: Wasm decoding failed: unexpected section: Code @+37433
RuntimeError: abort(CompileError: WasmCompile: Wasm decoding failed: unexpected section: Code @+37433) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at /home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7358365
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:189:7)
    at Function.Module.runMain (module.js:696:11)
    at startup (bootstrap_node.js:204:16)
    at bootstrap_node.js:625:3

Node 14 -- invalid threads opcode

RuntimeError: abort(RuntimeError: abort(CompileError: WebAssembly.instantiate(): Compiling function #73 failed: Invalid opcode (enable with --experimental-wasm-threads) @+39429) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at /home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7358365) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at process.abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at process.emit (events.js:315:20)
    at processPromiseRejections (internal/process/promises.js:245:33)
    at processTicksAndRejections (internal/process/task_queues.js:94:32)
    at process.abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33488)
    at process.emit (events.js:315:20)
    at processPromiseRejections (internal/process/promises.js:245:33)
    at processTicksAndRejections (internal/process/task_queues.js:94:32)

Rerunning with --experimental-wasm-threads produces invalid shared memory opcode instead

RuntimeError: abort(RuntimeError: abort(CompileError: WebAssembly.instantiate(): Compiling function #73 failed: Atomic opcodes used without shared memory @+39428) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at /home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7358365) at Error
    at jsStackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381549)
    at stackTrace (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:7381725)
    at process.abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33457)
    at process.emit (events.js:315:20)
    at processPromiseRejections (internal/process/promises.js:245:33)
    at processTicksAndRejections (internal/process/task_queues.js:94:32)
    at process.abort (/home/ubuntu/prog/docker-opencv/js_wasm/bin/opencv.js:31:33488)
    at process.emit (events.js:315:20)
    at processPromiseRejections (internal/process/promises.js:245:33)
    at processTicksAndRejections (internal/process/task_queues.js:94:32)

Steps to reproduce

1. Follow instructions here except for extra flags (see 2) https://docs.opencv.org/4.5.1/d4/da1/tutorial_js_setup.html

• using emsdk or docker didn't make any difference, nor the latest emsdk vs 2.0.10
• using --build_wasm or not also doesn't seem to matter (it always produces wasm)

2. Build with --build_test and --build_flags '-s ASSERTIONS=1'

sudo docker run --rm -v $(pwd):/src -u 1000:1000 emscripten/emsdk:2.0.10 emcmake python3 ./opencv/platforms/js/build_js.py js_assertions --build_test --build_flags '-s ASSERTIONS=1'

3. install node dependencies & run tests
4. change tests.js to run only for a single file (tests: [ 'test_mat.js' ]) & run tests
5. run node test_async.js

let cv

function loadOpenCv() {
    return new Promise(resolve => {
        global.Module = {
            onRuntimeInitialized: () => {
                console.log('opencv ready')
                resolve()
            }
        }
        cv = require('./opencv.js')
    })
}

loadOpenCv().then(() => {
    const mat = new cv.Mat(10, 20, cv.CV_8UC3)
    console.log(mat.cols)
    mat.delete()
})

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc

[alalek]

Perhaps you want to have something like "test_js" step from here.

I can confirm that specific versions of used software are required. Configuration of testing infrastructure is here.
Migration on newer node versions were failed, some extra build options are required.

[peteruhnak]

Thanks!

I can confirm that using emscripten 1.39.0-upstream I managed to build it and successfully run the test_async.js.

---

I can close this issue (as my main problem is solved), however I think these points still stand (so feel free to close the issue or keep it open):

• the docs should also mention emscripten 1.39.0-upstream for node (the recommended 2.0.10 is only ok for browser)
• node tests.js still fails due to the non-async loading

For the tests.js, I really don't understand why it works on the OpenCV build server. Digging through qunit/qunit-node source code, I didn't really see anything that would guarantee correct loading (which is also why it always fails for me); so I guess the CI server is getting a lucky race condition every time 🤷 (which is also weird).

[alalek]

Lets keep this open.
Hopefully some JS / Emscripten experts can suggest solutions / workarounds for mentioned issues.

[boulabiar]

I am having this issue with chrome mobile and firefox and many other browsers.
This is related to sharedarraybuffer or atomics that got activated after OpenCV 4.2. (4.2 works fine, but 4.4 doesn't work).

It seems like some work with optimisations and threads requested a still experimental feature in browsers and in node.
https://caniuse.com/sharedarraybuffer

When I force compiling a file using opencv wasm without threads in Emscripten (USE_PTHREADS=0), compilation fails because opencv wasm requested threads (and sharedarraybuffer) when it was compiled.
error message:
wasm-ld: error: 'atomics' feature is usedy alloc.cpp.o, so --shared-memory must be used.

There should be an option to compile without it.

[ValYouW]

Also trying to build opencv.js with --disable_wasm using latest emsdk (2.0.14) fails in the wasm2js command:

.../emsdk/upstream/bin/wasm2js --emscripten -O ../../bin/opencv_js.wasm --mvp-features --enable-threads --enable-mutable-globals --enable-bulk-memory --enable-sign-ext' failed (-6)

[exist2disappear]

i'm on 4.3.0 2021.4.21:
build with --disable_wasm.
err is :
em++: error: '/root/gitwork/emsdk/upstream/bin/wasm2js --emscripten -O ../../bin/opencv_js.wasm --mvp-features --enable-threads --enable-mutable-globals --enable-bulk-memory --enable-sign-ext' failed (-6)

what opt should use?

[rubuslab]

I think the key point is how to install build tool emscripten.
I installed emscripten-1.39.12 and build opencv.js success.
the steps as below:

1. install emscripten-1.39.12 and refine configuration
   (my main folder /data/develop-003/)
   rm /root/.emscripten* -rf
   git clone -b 1.39.12 https://github.com/emscripten-core/emsdk.git
   cd emsdk
   ./emsdk install 1.39.12
   ./emsdk activate 1.39.12
   cp /root/.emscripten ./
   source ./emsdk_env.sh

// test command
./upstream/emscripten/emcc -v

2. clone opencv and build wasm js
   git clone https://github.com/opencv/opencv.git
   cd opencv
   python3 ./platforms/js/build_js.py build_wasm_out --build_wasm --emscripten_dir=/data/develop-003/emsdk/upstream/emscripten/

May this can help you.

[dosgo]

Is this related to wasi?