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