File

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−/* managed_pointer.h
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−
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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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−
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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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−
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−USAGE
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−-----
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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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−
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−  fancy_buffer* new_buffer();
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−  void free_buffer(fancy_buffer* p_buffer)
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−
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−You could declare a managed version like so:
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−
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−  MANAGED_POINTER_ALLOCATOR(new_managed_buffer, fancy_buffer*, new_buffer, free_buffer)
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−
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−And then, when you need to create a new fancy_buffer in your code:
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−
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−  fancy_buffer *my_buffer = new_managed_buffer(L);
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−
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−NOTES
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−-----
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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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−
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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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−
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−#define MANAGED_POINTER_MT(wrapped_type) #wrapped_type "_managedptr_mt"
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−
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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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−