prosody
b001b0f42512
util-src/managed_pointer.h

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util-src/managed_pointer.h @ 12692:b001b0f42512

util-src: Add new utility header managed_pointer.h The macros in this header allow creation of GC-managed objects from manually- managed C alloc/free APIs.
author Matthew Wild <mwild1@gmail.com>
date Fri, 01 Jul 2022 15:11:08 +0100
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12691:90d90b540b6b 12692:b001b0f42512
1 /* managed_pointer.h
2
3 These macros allow wrapping an allocator/deallocator into an object that is
4 owned and managed by the Lua garbage collector.
5
6 Why? It is too easy to leak objects that need to be manually released, especially
7 when dealing with the Lua API which can throw errors from many operations.
8
9 USAGE
10 -----
11
12 For example, given an object that can be created or released with the following
13 functions:
14
15 fancy_buffer* new_buffer();
16 void free_buffer(fancy_buffer* p_buffer)
17
18 You could declare a managed version like so:
19
20 MANAGED_POINTER_ALLOCATOR(new_managed_buffer, fancy_buffer*, new_buffer, free_buffer)
21
22 And then, when you need to create a new fancy_buffer in your code:
23
24 fancy_buffer *my_buffer = new_managed_buffer(L);
25
26 NOTES
27 -----
28
29 Managed objects MUST NOT be freed manually. They will automatically be
30 freed during the next GC sweep after your function exits (even if via an error).
31
32 The managed object is pushed onto the stack, but should generally be ignored,
33 but you'll need to bear this in mind when creating managed pointers in the
34 middle of a sequence of stack operations.
35 */
36
37 #define MANAGED_POINTER_MT(wrapped_type) #wrapped_type "_managedptr_mt"
38
39 #define MANAGED_POINTER_ALLOCATOR(name, wrapped_type, wrapped_alloc, wrapped_free) \
40 static int _release_ ## name(lua_State *L) { \
41 wrapped_type *p = (wrapped_type*)lua_topointer(L, 1); \
42 if(*p != NULL) { \
43 wrapped_free(*p); \
44 } \
45 return 0; \
46 } \
47 static wrapped_type name(lua_State *L) { \
48 wrapped_type *p = (wrapped_type*)lua_newuserdata(L, sizeof(wrapped_type)); \
49 if(luaL_newmetatable(L, MANAGED_POINTER_MT(wrapped_type)) != 0) { \
50 lua_pushcfunction(L, _release_ ## name); \
51 lua_setfield(L, -2, "__gc"); \
52 } \
53 lua_setmetatable(L, -2); \
54 *p = wrapped_alloc(); \
55 if(*p == NULL) { \
56 lua_pushliteral(L, "not enough memory"); \
57 lua_error(L); \
58 } \
59 return *p; \
60 }
61