The Blocks C extension and GIO asynchronous calls

By kov

So, I intended to be completely away from my computer during my vacations, but hey. I have been interested in this new extension Apple added to the C language a little while ago which introduces the equivalent of closures to C. Today I spent a few minutes looking into it and writing a few tests with the help of clang.

Here’s something I came up with, to use a block as the callback for a GIO asynchronous call:

#include <Block.h>
#include <gio/gio.h>

typedef void (^Block)();

static void async_result_cb(GObject *source,
                              GAsyncResult *res,
                              gpointer data)
{
    Block block = (Block)data;
    block(res);
}

int main(int argc, char **argv)
{
    g_type_init();

    if (argc != 2) {
        g_error("Blah.");
        return 1;
    }

    GMainLoop *loop = g_main_loop_new(NULL, TRUE);
    GFile *file = g_file_new_for_path(argv[1]);

    g_file_query_info_async(
        file,
        G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE,
        G_FILE_QUERY_INFO_NONE, G_PRIORITY_DEFAULT,
        NULL, async_result_cb, (gpointer) ^ (GAsyncResult * res) {
            GError *error = NULL;
            GFileInfo *info = g_file_query_info_finish(file, res, &error);

            if (error) {
                g_error("Failed: %s", error->message);
                g_error_free(error);
                return;
            }

            g_message("Content Type: %s",
                g_file_info_get_attribute_string(info, G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE));

            g_object_unref(info);
            g_main_loop_quit(loop);
        });

    g_main_loop_run(loop);
    g_object_unref(file);

    return 0;
}

Pretty neat, don’t you think? To build you need to use clang and have the blocks runtime installed (libblocksruntime-dev in Debian). Here’s the command I use:

$ clang -fblocks -o gio gio.c -lBlocksRuntime `pkg-config --cflags --libs gio-2.0`