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annotate util-src/managed_pointer.h @ 13114:025c38ee885d

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util.dependencies: Print tables itself to reduce number of imports Rationale: See diffstat When this module is imported, it ends up calling stty via term_width() in util.human.io.table(). When this happens outside of a terminal, the following message is sent to stdout: stty: 'standard input': Inappropriate ioctl for device Not importing this module avoids that. Furthermore three is value in this module having minimal dependencies as they might not be available when it does the checks. Ref a1fed82c44b9
author Kim Alvefur <zash@zash.se>
date Fri, 26 May 2023 21:18:27 +0200
parents b001b0f42512
children
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1 /* managed_pointer.h
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2
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3 These macros allow wrapping an allocator/deallocator into an object that is
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4 owned and managed by the Lua garbage collector.
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5
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6 Why? It is too easy to leak objects that need to be manually released, especially
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7 when dealing with the Lua API which can throw errors from many operations.
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8
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9 USAGE
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10 -----
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11
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12 For example, given an object that can be created or released with the following
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13 functions:
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14
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15 fancy_buffer* new_buffer();
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16 void free_buffer(fancy_buffer* p_buffer)
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17
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18 You could declare a managed version like so:
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19
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20 MANAGED_POINTER_ALLOCATOR(new_managed_buffer, fancy_buffer*, new_buffer, free_buffer)
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21
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22 And then, when you need to create a new fancy_buffer in your code:
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23
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24 fancy_buffer *my_buffer = new_managed_buffer(L);
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25
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26 NOTES
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27 -----
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28
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29 Managed objects MUST NOT be freed manually. They will automatically be
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30 freed during the next GC sweep after your function exits (even if via an error).
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31
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32 The managed object is pushed onto the stack, but should generally be ignored,
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33 but you'll need to bear this in mind when creating managed pointers in the
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34 middle of a sequence of stack operations.
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35 */
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36
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37 #define MANAGED_POINTER_MT(wrapped_type) #wrapped_type "_managedptr_mt"
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38
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39 #define MANAGED_POINTER_ALLOCATOR(name, wrapped_type, wrapped_alloc, wrapped_free) \
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40 static int _release_ ## name(lua_State *L) { \
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41 wrapped_type *p = (wrapped_type*)lua_topointer(L, 1); \
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42 if(*p != NULL) { \
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43 wrapped_free(*p); \
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44 } \
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45 return 0; \
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46 } \
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47 static wrapped_type name(lua_State *L) { \
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48 wrapped_type *p = (wrapped_type*)lua_newuserdata(L, sizeof(wrapped_type)); \
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49 if(luaL_newmetatable(L, MANAGED_POINTER_MT(wrapped_type)) != 0) { \
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50 lua_pushcfunction(L, _release_ ## name); \
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51 lua_setfield(L, -2, "__gc"); \
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52 } \
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53 lua_setmetatable(L, -2); \
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54 *p = wrapped_alloc(); \
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55 if(*p == NULL) { \
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56 lua_pushliteral(L, "not enough memory"); \
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57 lua_error(L); \
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58 } \
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59 return *p; \
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60 }
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