From ff14b4a939511d42aa0ca46ea2139637b74e6e8a Mon Sep 17 00:00:00 2001
From: sanine <sanine.not@pm.me>
Date: Tue, 4 Oct 2022 15:22:22 -0500
Subject: add garbage collector canaries

---
 demo/minimal/main.lua |  1 +
 src/main.c            |  3 ++-
 src/util/util.c       | 45 +++++++++++++++++++++++++++++++++++++++++++++
 src/util/util.h       |  1 +
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/demo/minimal/main.lua b/demo/minimal/main.lua
index 8eaa5c1..28a8cbe 100644
--- a/demo/minimal/main.lua
+++ b/demo/minimal/main.lua
@@ -1 +1,2 @@
 print('hello, world!')
+local canary = honey.util.gc_canary(function() print('collecting canary') end)
diff --git a/src/main.c b/src/main.c
index 2a2880a..b825ff4 100644
--- a/src/main.c
+++ b/src/main.c
@@ -34,8 +34,9 @@ int main(int argc, char **argv)
 	setup_image(L, honey_index);
 	setup_import(L, honey_index);
 	setup_logging(L, honey_index);
-	setup_window(L, honey_index);
 	setup_ode(L, honey_index);
+	setup_util(L, honey_index);
+	setup_window(L, honey_index);
 	lua_setglobal(L, "honey");
 
 	/* load main script */
diff --git a/src/util/util.c b/src/util/util.c
index 84edd27..89e9d38 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -1,4 +1,6 @@
 #include <lua.h>
+#include <lauxlib.h>
+#include <honeysuckle.h>
 
 void append_table(lua_State *L, int tbl_a, int tbl_b)
 {
@@ -10,3 +12,46 @@ void append_table(lua_State *L, int tbl_a, int tbl_b)
 		lua_pop(L, 1);
 	}
 }
+
+
+const char *canary_tname = "honey.canary";
+
+int gc_canary(lua_State *L);
+int gc_canary_collect(lua_State *L);
+
+void setup_util(lua_State *L, int honey_tbl)
+{
+	/* create gc_canary metatable */
+	luaL_newmetatable(L, canary_tname);
+	lua_pushcfunction(L, gc_canary_collect);
+	lua_setfield(L, -2, "__gc");
+	lua_pop(L, 1);
+
+	hs_create_table(L,
+		hs_str_cfunc("gc_canary", gc_canary),
+	);
+
+	lua_setfield(L, honey_tbl, "util");
+}
+
+
+int gc_canary(lua_State *L)
+{
+	luaL_checktype(L, 1, LUA_TFUNCTION);
+	int ref = luaL_ref(L, LUA_REGISTRYINDEX);
+	int *canary = lua_newuserdata(L, sizeof(int));
+	*canary = ref;
+	luaL_getmetatable(L, canary_tname);
+	lua_setmetatable(L, -2);
+	return 1;
+}
+
+
+int gc_canary_collect(lua_State *L)
+{
+	int *canary = luaL_checkudata(L, 1, canary_tname);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, *canary);
+	lua_call(L, 0, 0);
+	luaL_unref(L, LUA_REGISTRYINDEX, *canary);
+	return 0;
+}
diff --git a/src/util/util.h b/src/util/util.h
index 3ef4e0b..231bcc9 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -3,6 +3,7 @@
 
 #include <lua.h>
 
+void setup_util(lua_State *L, int honey_tbl);
 void append_table(lua_State *L, int tbl_a, int tbl_b);
 
 #endif
-- 
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