A utility library for coroutines in Emscripten (using Asyncify)

Coroutines

emcc example.c -s ASYNCIFY \
  -s ASYNCIFY_IMPORTS='["emscripten_sleep","emscripten_yield","emscripten_coroutine_create","emscripten_coroutine_next"]' \
  --js-library library_coroutine.js

example.c

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

void cofunc(void *data) {
    printf("co: 1\n");
    emscripten_yield();
    printf("co: 2\n");
    emscripten_yield();
    printf("co: 3\n");
}

int main(int argc, char **argv) {
    emscripten_coroutine co = emscripten_coroutine_create(cofunc, NULL, 64 * 1024);
    printf("main: 1\n");
    emscripten_coroutine_next(co);
    printf("main: 2\n");
    emscripten_coroutine_next(co);
    printf("main: 3\n");
    emscripten_coroutine_next(co);
    printf("-------\n");
}

library_coroutine.js

mergeInto(LibraryManager.library, {

  $Coroutines__deps: ["Asyncify_restoreState"],
  $Coroutines: {
    main: null, live: [], active: null,
    allocate: function(obj) {
      id = this.live.length;
      this.live[id] = obj;
      return id;
    },
    free: function(id) {
      delete this.live[id];
    },
    resume: function(co) {
      _Asyncify_restoreState(co.savedState);
      co.jump();
    },
    return: function(id) {
      this.free(id);
      this.resume(this.main);
    }
  },

  assign$: function(to, from) { for (let k in from) to[k] = from[k]; },

  Asyncify_saveState: function() {
    return {currData: Asyncify.currData};
  },

  Asyncify_restoreState__deps: ["assign$"],
  Asyncify_restoreState: function(savedState) {
    _assign$(Asyncify, savedState);
  },

  emscripten_coroutine_create__deps: ["$Coroutines"],
  emscripten_coroutine_create: function(funcptr, data, size) {
    return Coroutines.allocate(
        {jump: () => Module.asm.dynCall_vi(funcptr, data), savedState: {}});
  },
  
  emscripten_coroutine_next__deps: ["$Coroutines", "Asyncify_saveState"],
  emscripten_coroutine_next: function(id) {
    co = Coroutines.live[id];
    return Asyncify.handleSleep((wakeUp) => {
      setTimeout(() => {
        Coroutines.main = {jump: wakeUp, savedState: _Asyncify_saveState()};
        Coroutines.active = co;
        Coroutines.resume(co);
        if (!Asyncify.currData) Coroutines.return(id);
      });
    });
  },

  emscripten_yield__deps: ["assign$", "Asyncify_saveState"],
  emscripten_yield: function() {
      return Asyncify.handleSleep((wakeUp) => {
        setTimeout(() => {
          _assign$(Coroutines.active,
              {jump: wakeUp, savedState: _Asyncify_saveState()});
          Coroutines.resume(Coroutines.main);
      });
    });
  },

});