doc/ext_c_api.html

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  13 <a href="https://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
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  16 <h1>Lua/C API Extensions</h1>
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  57 <p>
  58 LuaJIT adds some extensions to the standard Lua/C API. The LuaJIT include
  59 directory must be in the compiler search path (<tt>-I<i>path</i></tt>)
  60 to be able to include the required header for C code:
  61 </p>
  62 <pre class="code">
  63 #include "luajit.h"
  64 </pre>
  65 <p>
  66 Or for C++ code:
  67 </p>
  68 <pre class="code">
  69 #include "lua.hpp"
  70 </pre>
  71
  72 <h2 id="luaJIT_setmode"><tt>luaJIT_setmode(L, idx, mode)</tt>
  73 &mdash; Control VM</h2>
  74 <p>
  75 This is a C API extension to allow control of the VM from C code. The
  76 full prototype of <tt>LuaJIT_setmode</tt> is:
  77 </p>
  78 <pre class="code">
  79 LUA_API int luaJIT_setmode(lua_State *L, int idx, int mode);
  80 </pre>
  81 <p>
  82 The returned status is either success (<tt>1</tt>) or failure (<tt>0</tt>).
  83 The second argument is either <tt>0</tt> or a stack index (similar to the
  84 other Lua/C API functions).
  85 </p>
  86 <p>
  87 The third argument specifies the mode, which is 'or'ed with a flag.
  88 The flag can be <tt>LUAJIT_MODE_OFF</tt> to turn a feature off,
  89 <tt>LUAJIT_MODE_ON</tt> to turn a feature on, or
  90 <tt>LUAJIT_MODE_FLUSH</tt> to flush cached code.
  91 </p>
  92 <p>
  93 The following modes are defined:
  94 </p>
  95
  96 <h3 id="mode_engine"><tt>luaJIT_setmode(L, 0, LUAJIT_MODE_ENGINE|flag)</tt></h3>
  97 <p>
  98 Turn the whole JIT compiler on or off or flush the whole cache of compiled code.
  99 </p>
 100
 101 <h3 id="mode_func"><tt>luaJIT_setmode(L, idx, LUAJIT_MODE_FUNC|flag)</tt><br>
 102 <tt>luaJIT_setmode(L, idx, LUAJIT_MODE_ALLFUNC|flag)</tt><br>
 103 <tt>luaJIT_setmode(L, idx, LUAJIT_MODE_ALLSUBFUNC|flag)</tt></h3>
 104 <p>
 105 This sets the mode for the function at the stack index <tt>idx</tt> or
 106 the parent of the calling function (<tt>idx = 0</tt>). It either
 107 enables JIT compilation for a function, disables it and flushes any
 108 already compiled code, or only flushes already compiled code. This
 109 applies recursively to all sub-functions of the function with
 110 <tt>LUAJIT_MODE_ALLFUNC</tt> or only to the sub-functions with
 111 <tt>LUAJIT_MODE_ALLSUBFUNC</tt>.
 112 </p>
 113
 114 <h3 id="mode_trace"><tt>luaJIT_setmode(L, trace,<br>
 115 &nbsp;&nbsp;LUAJIT_MODE_TRACE|LUAJIT_MODE_FLUSH)</tt></h3>
 116 <p>
 117 Flushes the specified root trace and all of its side traces from the cache.
 118 The code for the trace will be retained as long as there are any other
 119 traces which link to it.
 120 </p>
 121
 122 <h3 id="mode_wrapcfunc"><tt>luaJIT_setmode(L, idx, LUAJIT_MODE_WRAPCFUNC|flag)</tt></h3>
 123 <p>
 124 This mode defines a wrapper function for calls to C functions. If
 125 called with <tt>LUAJIT_MODE_ON</tt>, the stack index at <tt>idx</tt>
 126 must be a <tt>lightuserdata</tt> object holding a pointer to the wrapper
 127 function. From now on, all C functions are called through the wrapper
 128 function. If called with <tt>LUAJIT_MODE_OFF</tt> this mode is turned
 129 off and all C functions are directly called.
 130 </p>
 131 <p>
 132 The wrapper function can be used for debugging purposes or to catch
 133 and convert foreign exceptions. But please read the section on
 134 <a href="extensions.html#exceptions">C++&nbsp;exception interoperability</a>
 135 first. Recommended usage can be seen in this C++ code excerpt:
 136 </p>
 137 <pre class="code">
 138 #include &lt;exception&gt;
 139 #include "lua.hpp"
 140
 141 // Catch C++ exceptions and convert them to Lua error messages.
 142 // Customize as needed for your own exception classes.
 143 static int wrap_exceptions(lua_State *L, lua_CFunction f)
 144 {
 145   try {
 146     return f(L);  // Call wrapped function and return result.
 147   } catch (const char *s) {  // Catch and convert exceptions.
 148     lua_pushstring(L, s);
 149   } catch (std::exception& e) {
 150     lua_pushstring(L, e.what());
 151   } catch (...) {
 152     lua_pushliteral(L, "caught (...)");
 153   }
 154   return lua_error(L);  // Rethrow as a Lua error.
 155 }
 156
 157 static int myinit(lua_State *L)
 158 {
 159   ...
 160   // Define wrapper function and enable it.
 161   lua_pushlightuserdata(L, (void *)wrap_exceptions);
 162   luaJIT_setmode(L, -1, LUAJIT_MODE_WRAPCFUNC|LUAJIT_MODE_ON);
 163   lua_pop(L, 1);
 164   ...
 165 }
 166 </pre>
 167 <p>
 168 Note that you can only define <b>a single global wrapper function</b>,
 169 so be careful when using this mechanism from multiple C++ modules.
 170 Also note that this mechanism is not without overhead.
 171 </p>
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