prosody
245ffbb06f55
util-src/managed_pointer.h

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util-src/managed_pointer.h @ 12929:245ffbb06f55

util.jwt: Import definition of key from util.crypto Turns out we had a definition of that already
author Kim Alvefur <zash@zash.se>
date Fri, 10 Mar 2023 13:58:43 +0100
parent 12692:b001b0f42512
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
12692
b001b0f42512 util-src: Add new utility header managed_pointer.h
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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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