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-rw-r--r--util-src/managed_pointer.h61
1 files changed, 61 insertions, 0 deletions
diff --git a/util-src/managed_pointer.h b/util-src/managed_pointer.h
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+++ b/util-src/managed_pointer.h
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+/* managed_pointer.h
+
+These macros allow wrapping an allocator/deallocator into an object that is
+owned and managed by the Lua garbage collector.
+
+Why? It is too easy to leak objects that need to be manually released, especially
+when dealing with the Lua API which can throw errors from many operations.
+
+USAGE
+-----
+
+For example, given an object that can be created or released with the following
+functions:
+
+ fancy_buffer* new_buffer();
+ void free_buffer(fancy_buffer* p_buffer)
+
+You could declare a managed version like so:
+
+ MANAGED_POINTER_ALLOCATOR(new_managed_buffer, fancy_buffer*, new_buffer, free_buffer)
+
+And then, when you need to create a new fancy_buffer in your code:
+
+ fancy_buffer *my_buffer = new_managed_buffer(L);
+
+NOTES
+-----
+
+Managed objects MUST NOT be freed manually. They will automatically be
+freed during the next GC sweep after your function exits (even if via an error).
+
+The managed object is pushed onto the stack, but should generally be ignored,
+but you'll need to bear this in mind when creating managed pointers in the
+middle of a sequence of stack operations.
+*/
+
+#define MANAGED_POINTER_MT(wrapped_type) #wrapped_type "_managedptr_mt"
+
+#define MANAGED_POINTER_ALLOCATOR(name, wrapped_type, wrapped_alloc, wrapped_free) \
+ static int _release_ ## name(lua_State *L) { \
+ wrapped_type *p = (wrapped_type*)lua_topointer(L, 1); \
+ if(*p != NULL) { \
+ wrapped_free(*p); \
+ } \
+ return 0; \
+ } \
+ static wrapped_type name(lua_State *L) { \
+ wrapped_type *p = (wrapped_type*)lua_newuserdata(L, sizeof(wrapped_type)); \
+ if(luaL_newmetatable(L, MANAGED_POINTER_MT(wrapped_type)) != 0) { \
+ lua_pushcfunction(L, _release_ ## name); \
+ lua_setfield(L, -2, "__gc"); \
+ } \
+ lua_setmetatable(L, -2); \
+ *p = wrapped_alloc(); \
+ if(*p == NULL) { \
+ lua_pushliteral(L, "not enough memory"); \
+ lua_error(L); \
+ } \
+ return *p; \
+ }
+