Is it possible to use OPFS backend with -sASYNCIFY=1?

[pashokitsme]

Hi.
I'm trying to use OPFS without -pthread or -sASYNCIFY=2:

• -pthread needs additional cors headers that SharedArrayBuffer requires to work
• -sASYNCIFY=2 needs experimental features that not available in firefox (for example)

I saw that code about jspi/pthread but maybe there is another way to use OPFS?

If i compiling with (or without but it obviously ends up with an error in runtime) -sASYNCIFY=1 i get:

Example code which runs in main thread for jspi and in worker for everything else

#include <emscripten.h>
#include <emscripten/wasmfs.h>
#include <stdio.h>

int main(void) {
  backend_t opfs_backend = wasmfs_create_opfs_backend();
  int err = wasmfs_create_directory("/opfs", 0777, opfs_backend);
  if (err) {
    fprintf(stderr, "wasmfs_create_directory err: %d\n", err);
    return err;
  }

  FILE *file = fopen("/opfs/x", "wb");
  if (!file) {
    fprintf(stderr, "fopen err\n");
    return -1;
  }

  return 0;
}

Flags i used:

• -sASYNCIFY=2: emcc main.c -sWASM=1 -sWASMFS=1 -sEXPORT_ES6=1 -sASYNCIFY=2 -o dist/out.js
• -sASYNCIFY: emcc main.c -sWASM=1 -sWASMFS=1 -sEXPORT_ES6=1 -sASYNCIFY -o dist/out.js
• -pthread: emcc main.c -sWASM=1 -sWASMFS=1 -lopfs.js -pthread -sPROXY_TO_PTHREAD=1 -sEXPORT_ES6=1 -o dist/out.js

[sbc100]

@tlively

[tlively]

@brendandahl wrote the Asyncify integration for the OPFS backend. Looking at the code, nothing jumps out as preventing it from working with ASYNCIFY=1, but he would know best.

[brendandahl]

It's definitely possible, but currently asyncify=1 and asyncify=2 change the API in JS in different ways (e.g. jspi = always returns promise vs asyncify requires handling unwinds) so I'm not surprised it's broken.

[pashokitsme]

So that asyncify=1 not working currently is a bug?

[brendandahl]

We haven't done any work to implement it, so I'd say it's more a missing feature.

[pashokitsme]

Is there any hope that it will be implemented?

[pashokitsme]

@brendandahl ?

[brendandahl]

It's not currently planned for the near future. We've talked of unifying ASYNCIFY=1 and ASYNCIFY=2 so they behave the same, but it's a low priority. Even without making them behave the same it should be possible to get opfs to work with asyncify=1.

[pashokitsme]

I've tried to do something with proxy & wasmfsOPFSProxyFinish and came up (just for test) with the most stupid solution like while(!ready) emscripten_sleep(0); which works on simple scenarios but fails on a bit more complicated because of multiple async ops. Not even sure it relates to asyncify 😓

I guess the clue is here, isn't it? And i need to use ProxyQueue instead?
Would be cool to get it work but no idea how exactly.