From 031636cfb340a13585d9a10917aed76dc1e6818b Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Mon, 25 Sep 2023 17:18:18 +0200
Subject: [PATCH 1/2] Handle null pointer in async_cb_dispatcher mark and free

Fix: https://github.com/ffi/ffi/issues/1050

I don't fully understand that code, so my fix might be totally
off. But according to production crashes, `ctx` might be NULL
sometimes.
---
 ext/ffi_c/Function.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/ext/ffi_c/Function.c b/ext/ffi_c/Function.c
index 78100563a..996d7b75e 100644
--- a/ext/ffi_c/Function.c
+++ b/ext/ffi_c/Function.c
@@ -166,14 +166,18 @@ static void
 async_cb_dispatcher_mark(void *ptr)
 {
     struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)ptr;
-    rb_gc_mark(ctx->thread);
+    if (ctx) {
+        rb_gc_mark(ctx->thread);
+    }
 }
 
 static void
 async_cb_dispatcher_free(void *ptr)
 {
     struct async_cb_dispatcher *ctx = (struct async_cb_dispatcher *)ptr;
-    xfree(ctx);
+    if (ctx) {
+        xfree(ctx);
+    }
 }
 
 struct rb_ractor_local_storage_type async_cb_dispatcher_key_type = {

From 97ce4efd11582e74fcf24493f80b94cb786a6e7f Mon Sep 17 00:00:00 2001
From: Lars Kanis <lars@greiz-reinsdorf.de>
Date: Mon, 25 Sep 2023 20:28:32 +0200
Subject: [PATCH 2/2] Add test case for #1050

Fixing commit is 031636cfb340a13585d9a10917aed76dc1e6818b
---
 spec/ffi/fork_spec.rb | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/spec/ffi/fork_spec.rb b/spec/ffi/fork_spec.rb
index 2c663ee2a..421982df2 100644
--- a/spec/ffi/fork_spec.rb
+++ b/spec/ffi/fork_spec.rb
@@ -62,5 +62,14 @@ def run_async_callback(libtest)
 
       expect(Process.wait2[1].exitstatus).to eq(44)
     end
+
+    it "GC doesn't crash when the dispatcher thread was stopped. #1050" do
+      FFI::Function.new(:int, [], proc{})
+      fork do
+        GC.start
+        Process.exit 45
+      end
+      expect(Process.wait2[1].exitstatus).to eq(45)
+    end
   end
 end