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Difficulty integrating with Swift/Objective-C


From: paul
Subject: Difficulty integrating with Swift/Objective-C
Date: Sun, 05 Sep 2021 16:03:24 +1000
User-agent: mu4e 1.4.15; emacs 27.2

Good day,

I have an existing app which is written in Swift and runs on macOS 10.15. I would like to provide users a way of customising the app (initially just simple things like modifying keybindings for example, later hopefully more) and as a keen Emacs user, i'm inspired by the idea of providing a Schemey/Lispy interface for such extensions. Guile looks like it'd be great for this. If i understand correctly, it'd be best if i could bundle the Guile runtime as a static library with the app, and call out to it to evaluate user-provided code. I haven't thought deeply about this interface yet; i thought i'd get a proof-of-concept working first. I wonder if i might humbly ask for some guidance on how to get it working, because after a couple of days i seem to have failed. I'm no C/threads/low-level guru, so my apologies if i'm doing something very dumb.

I had some difficulty getting my app to compile against Guile, but i eventually managed to link against a version of Guile installed with Homebrew (guile: stable 3.0.7 (bottled)), however when trying to boot it up i seemed to run into the same issue described by Jeffrey Walton [1]. My app would boot, and as soon as it hit the Guile initialisation calls, it would error with "allocating JIT code buffer failed: Permission denied, jit.c:5804: fatal: assertion failed". While that person seems to imply the problem is with Apple's M1 silicon, i'm actually running an older machine (2.9 GHz Dual-Core Intel Core i5, macOS 11.5.2). I then managed to get further by downloading the Guile release tarball version 3.0.7 and and building with `./configure --enable-jit=no`; this got me a bit further, however it still didn't work: i think it is because some assumption Guile has about the thread it runs on, or when it's invoked, is violated.. but i'm unsure how to find out.

What i currently have, is this snippet. It's being called from Swift land, in the `applicationDidFinishLaunching(_ aNotification: Notification)` function. As far as i can tell, that _is_ the main thread.

```
#include "libguile.h"

static void* register_functions (void* data)
{
   SCM test = scm_c_eval_string("(+ 3 5)");
   int foo = scm_to_int(test);
   printf("foo = %d\n", foo);

   return NULL;
}

void run_guile() {
   printf("hello from C, before Guile\n");
   scm_init_guile();
//scm_with_guile(&register_functions, NULL); // i've tried only having this line uncommented, too, but that also causes immediate crashes
   //scm_shell(0, NULL);
}
```

This compiles fine, and i see the "hello from C" line printed, but then it crashes. The error seems to vary, here are some i've seen:

1. "Thread 1: EXC_BAD_ACCESS (code=1, address=0x0)" at line 182 of pairs.h, 2. "Pre-boot error; key: misc-error, args: ("%search-path" "path is not a proper list: ~a" (("/usr/local/share/guile/3.0" "/usr/local/share/guile/site/3.0" "/usr/local/share/guile/site" . #<program 12503b140 124fc10fc>)) #f)", "Thread 1: signal SIGABRT", line 260 of throw.c 3. "Thread 1: EXC_BAD_ACCESS (code=1, address=0x9)", at line 585 of weak-set.c. 4. I've also sometimes seen this one, https://lists.gnu.org/archive/html/emacs-bug-tracker/2020-01/msg00365.html, although perhaps that's indeed related to closed stdout.

Because these errors are different all the time i guess it's some race condition or threading issue? I wonder if someone knows an avenue i can attempt to use to debug what's going on? 🙏

All the best,
paul

1. https://mail.gnu.org/archive/html/bug-guile/2021-03/msg00012.html



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