author | Kim Alvefur <zash@zash.se> |
Fri, 21 Jul 2023 18:30:06 +0200 | |
changeset 13240 | 9c72f93b7a02 |
parent 12696 | b001b0f42512 |
permissions | -rw-r--r-- |
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/* 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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