Import function with struct/class parameters

[xzmqaq0307]

When using the import and export function, I encountered a problem where the structure is used as a parameter for the export function. However, when this function is imported into another wasm and used, the final output result is incorrect

utils.h

#ifndef UTILS_H
#define UTILS_H

#define WASM_EXPORT(name) __attribute__((export_name(name)))
#define WASM_IMPORT(mod, name) __attribute__((import_module(mod), import_name(name)))

struct MyObject {
	int val1 = 5;
	int val2 = 5;
	int val3 = 5;
	void resetAll() {
		val1 = 5;
		val2 = 5;
		val3 = 5;
	}
};
#endif

share.cpp (define export function)

#include "../inc/utils.h"
#include <stdint.h>

MyObject obj;

WASM_IMPORT("env", "print") extern void print(int num);
WASM_EXPORT("set_obj") void set_obj(MyObject val) {
	obj = val;
}

main.cpp (import functions which is exported by share.cpp)

#include "../inc/utils.h"
#include <stdint.h>

WASM_IMPORT("env", "print") extern void print(int num);
WASM_IMPORT("share_ctx", "set_obj") extern void set_obj(MyObject obj);

WASM_EXPORT("main_set_obj") void main_set_obj() {
	MyObject obj;
	obj.val1 = 1;
	obj.val2 = 2;
	obj.val3 = 3;
	set_obj(obj);
}

Can I pass the MyObject value and set it through the import 'set_obj' function ? the result is that all value is 0, which is not expected

[sbc100]

I are you attempting to make called between two different Wasm modules? If so the approach used here since, under normal circumstances, each module its its own separate program with it own separate memory. The val argument to set_obj will be passed as a pointer to location in memory, which will not be meaningful to the receiver which does not have access to the callers memory.

emscripten does have support for dynamic linking if you want to split your code into multiple modules. In this case you can would build the main.cpp with -sMAIN_MODULE and share.cpp with -sSIDE_MODULE. In this case you don't need to use the WASM_IMPORT or WASM_EXPORT macros.. this will just work without those.

If you want to get a minimally sided main module you can use -sMAIN_MODULE=2 but that also requires that you pass in the side module when linking the main module.

[xzmqaq0307]

@sbc100 I think I may need to describe my design ideas. it may something different from main_module and side module case. I am trying to design a data center module that exports get/set functions for other modules to import and use, in order to achieve data synchronization and sharing. My design idea is shown in the following figure:

I try to create a shared memory in JS, which instantiates various GlobalData.wasms in different webworkers, and then exports the functions of GlobalData.wasm to three wasms: A, B, and C to achieve global data (only one copy exists in memory).

Do I need to copy these objects defined by structures in JS (ex. new Uint8Array(memory, pointer, offsert)), in order to pass them to other wasms for use? but this happens memory copying. Is it possible for two wasms to synchronize data through shared memory or any other ways?

Because there are many complex data structure definitions inside, I hope to achieve global data control through this method instead of controlling within JS. I'm not sure if this design is reasonable. If it's not reasonable or there's a better solution, I hope you can point it out without getting tired of it. Thanks ! :)