Pass Go function to C as callback

Question

Suppose I have a C library with code like this:

typedef int (callback_t)(int);
void register_callback(callback_t cb);

I want to write go bindings for this function and pass arbitrary go callbacks.

I found an excellent answer here. However, it is a trick that makes use of the fact that the callback accepts a void *, through which Go passes the function pointer to C and receives it back. However, this can't be applied in my example since there isn't a user void *.

The best I could do is:

/*
extern int gobridge(int data);

static int cbridge(void)
{
    register_callback(gobridge);
}
*/
import "C"

type Callback func (int) int

var g_cb Callback

//export gobridge
func gobridge(data C.int) C.int {
    return C.int(g_cb(int(data)))
}

func RegisterCallback(cb Callback) {
    g_cb = cb //save callback in a global
    C.cbridge()
}

func Count(left, right int) {
    C.count(C.int(left), C.int(right))
}

This only works for a single register_callback (because of the global variable), but the C library can register many callbacks and invoke them all.

I hoped to achieve something like this, but this doesn't compile (put aside the clojure, it can't convert the go function to c function even though the signature is the same):

import "C"

func RegisterCallback(cb Callback) {
    f := func (d C.int) C.int {
        return C.int(cb(int(d)))
    }
    C.register_callback(f)
}

func Count(left, right int) {
    C.count(C.int(left), C.int(right))
}

Is there a way to properly bind the C library?

Have you read through https://github.com/golang/go/wiki/cgo? There's a number of examples there. — JimB, Jun 08 '16 at 13:44
@JimB, couldn't find a single appropriate example there, can you point to one? — kaspersky, Jun 08 '16 at 13:59

score 0 · Answer 1 · answered Apr 26 '17 at 20:23

0

You could create an array of callbacks and have the bridge iterate the array of callbacks if the there is no return value (void function).

answered Apr 26 '17 at 20:23

rouzier

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Pass Go function to C as callback

1 Answers1