doc/ext_c_api.html

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