[RuntimeError: unreachable] Retrieving from async function in C++

[fidel espanto]

I'm trying to call an async function, 'isConfigSupported' from WebCodecs API.

Here is what I did in C++,

val VideoDecoder = val::global("VideoDecoder");

   ConfigCodec* config = new ConfigCodec(); // some struct

   config->codec = "vp8";

   config->codedWidth = 640;

   config->codedHeight = 480;

   val result = VideoDecoder.call<val>("isConfigSupported", config).await();

   

   if (result["supported"].as<bool>()) {

      EM_ASM(

         console.log("Codec is supported");

      );

   } else {

      EM_ASM(

         console.error("Codec is not supported");

      );

   }

I have compiled emcc with this additional option, '-O3 -sASYNCIFY' as stated in the documentation.

The result is 'Codec is supported', however, I get an error in the console logs,

wasmapi.wasm:0x1e79f Uncaught (in promise) RuntimeError: unreachable
    at wasmapi.wasm:0x1e79f
    at wasmapi.wasm:0x1ca34
    at wasmapi.wasm:0x118be
    at ret.<computed> (wasmapi.js:1:87071)
    at Object.doRewind (wasmapi.js:1:88672)
    at wasmapi.js:1:89246

Did I miss something? What does this error mean?

[Sam Clegg]

If you build with `-g` (or just `--profiling-funcs`) when you should see symbol names in your backtrace which might help you figure out what is going on.  You might also want to drop the `-O3` when debugging too.

BTW, we have `emscripten_console_log` and `emscripten_console_error` functions so you shouldn't need to write EM_ASM blocks just to write to the console.

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