luaL_error与c++ stack unwind的冲突

　　一般在用c写的lua函数里，检测到某些参数或前置条件错误时，会用luaL_error来报错，这时脚本层如果是xpcall，其错误处理函数就会被调用，在其中可用debug.traceback()来打印记录错误栈，这是脚本错误调试的常用做法。

　　但是在c++环境中使用lua时，却有一个细微而致命的bug：lua通常是按c语言方式编译，因此luaL_error最终会调用longjump来实现跨函数远程跳转，而这种跳转不会遵循c++关于stack unwinding的规范，其最直接的影响就是局部变量的析构函数不会被调用。

　　如果使用的是官方版lua，那么可以用c++方式编译lua来解决。但是如果用的luajit，它本身是不支持c++编译的（很多语法错误），那只有自求多福了，在luajit的网站上对此也有说明:

C++ Exception Interoperability

LuaJIT has built-in support for interoperating with C++ exceptions. The available range of features depends on the target platform and the toolchain used to compile LuaJIT:

Platform	Compiler	Interoperability
POSIX/x64, DWARF2 unwinding	GCC 4.3+	Full
Other platforms, DWARF2 unwinding	GCC	Limited
Windows/x64	MSVC or WinSDK	Full
Windows/x86	Any	No
Other platforms	Other compilers	No

Full interoperability means:

• C++ exceptions can be caught on the Lua side with pcall(), lua_pcall() etc.
• C++ exceptions will be converted to the generic Lua error "C++ exception", unless you use the C call wrapper feature.
• It's safe to throw C++ exceptions across non-protected Lua frames on the C stack. The contents of the C++ exception object pass through unmodified.
• Lua errors can be caught on the C++ side with catch(...). The corresponding Lua error message can be retrieved from the Lua stack.
• Throwing Lua errors across C++ frames is safe. C++ destructors will be called.

Limited interoperability means:

• C++ exceptions can be caught on the Lua side with pcall(), lua_pcall() etc.
• C++ exceptions will be converted to the generic Lua error "C++ exception", unless you use the C call wrapper feature.
• C++ exceptions will be caught by non-protected Lua frames and are rethrown as a generic Lua error. The C++ exception object will be destroyed.
• Lua errors cannot be caught on the C++ side.
• Throwing Lua errors across C++ frames will not call C++ destructors.

No interoperability means:

• It's  not safe to throw C++ exceptions across Lua frames.

• C++ exceptions  cannot be caught on the Lua side.

• Lua errors  cannot be caught on the C++ side.

• Throwing Lua errors across C++ frames will  not call C++ destructors.

• Additionally, on Windows/x86 with SEH-based C++ exceptions: it's  not safe to throw a Lua error across any frames containing a C++ function with any try/catch construct or using variables with (implicit) destructors. This also applies to any functions which may be inlined in such a function. It doesn't matter whether  lua_error() is called inside or outside of a try/catch or whether any object actually needs to be destroyed: the SEH chain is corrupted and this will eventually lead to the termination of the process.

　　在x86平台上是完全不支持的。那么解决办法只有一条：自己保证luaL_error的调用不会冲掉局部对象的析构函数。在同一个函数里，一般可以用无条件的块来人为分隔作用域，如：

{
  std::string s="abc";
  ...
}
luaL_error(L,...);

　　但是如果上层函数中还有局部对象，那只有自己根据具体的业务需求做调整了。通常来说，通过lua_register注册的c函数，其上层调用就是lua函数了，因此只要管好从它到抛出错误的点之间的调用路径上，没有被冲击的局部对象即可。但如果调用该c函数的lua函数，本身又是从另一个c函数里调过来的，该怎样考虑呢？很简单，从c里调lua时，必须包在pcall里，这样抛上来的错误就一定到此截止了。