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