LUA源码分析七:require的函数调用堆栈

require的调用其实很简单，熟悉完env的设置后，其实本质上都是走luaL_dofile函数对全局表的设置。do_file完，然后设置环境变量。借助此，把LUA里的函数堆栈方式依次跟调一次。

如果是熟悉汇编堆栈的形式，对LUA的源码风格很好理解。比如没有实际的变量名，通过对栈的偏移来访问。大于0的表示从base基地址加起，负数的表示从top往后减，或者是表示特定的全局值。因为有这种访问上的规则，所以lua的源码对访问封装的层次很清晰，哪里要回退栈指针，哪里要增加top地址等等。

static int ll_require (lua_State *L) {  const char *name = luaL_checkstring(L, 1);  int i;  lua_settop(L, 1);  /* _LOADED table will be at index 2 */  lua_getfield(L, LUA_REGISTRYINDEX, "_LOADED");  lua_getfield(L, 2, name);  if (lua_toboolean(L, -1)) {  /* is it there? */    if (lua_touserdata(L, -1) == sentinel)  /* check loops */      luaL_error(L, "loop or previous error loading module " LUA_QS, name);    return 1;  /* package is already loaded */  }  /* else must load it; iterate over available loaders */  lua_getfield(L, LUA_ENVIRONINDEX, "loaders");  if (!lua_istable(L, -1))    luaL_error(L, LUA_QL("package.loaders") " must be a table");  lua_pushliteral(L, "");  /* error message accumulator *//*至此栈的数据0x00395108:LUA_REGISTRYINDEX, "_LOADED"0x00395118:lua_getfield(L, 2, name)  //name,导入的模块名0x00395128:LUA_ENVIRONINDEX, "loaders"0x00395138:""*/  for (i=1; ; i++) {/*i=1:从0x00395128取值赋到栈顶0x00395148:LUA_ENVIRONINDEX, "loaders"[1]i=2:从0x00395128取值赋到栈顶0x00395148:LUA_ENVIRONINDEX, "loaders"[2]*/    lua_rawgeti(L, -2, i);  /* get a loader */    if (lua_isnil(L, -1))      luaL_error(L, "module " LUA_QS " not found:%s",                    name, lua_tostring(L, -2));/*i=1:0x00395158:lua_pushstring(L, name);i=2:0x00395158:lua_pushstring(L, name);*/    lua_pushstring(L, name);/*i=1:呼叫0x00395148的函数，name做为参数。呼叫过程见段1i=2:呼叫0x00395148的函数，name做为参数。呼叫过程见段2*/    lua_call(L, 1, 1);  /* call it *//*i=1:判断是否找到模块名*/    if (lua_isfunction(L, -1))  /* did it find module? */      break;  /* module loaded successfully */    else if (lua_isstring(L, -1))  /* loader returned error message? */      lua_concat(L, 2);  /* accumulate it */    else      lua_pop(L, 1);  }/*0x00395158:sentinel*/  lua_pushlightuserdata(L, sentinel);/*基地址是L->base = 0x003950f8，取到0x00395108:LUA_REGISTRYINDEX, "_LOADED"值。把top的值(sentinel)给_LOADED[name],同时top--*/  lua_setfield(L, 2, name);  /* _LOADED[name] = sentinel *//*0x00395158:lua_pushstring(L, name)*/  lua_pushstring(L, name);  /* pass name as argument to module *//*  调用,将模块环境载入.并且修改了0x00395148函数块,压入一个lua的函数调用结构*/  lua_call(L, 1, 1);  /* run loaded module */  if (!lua_isnil(L, -1))  /* non-nil return? */    lua_setfield(L, 2, name);  /* _LOADED[name] = returned value *//*0x00395158:lua_pushstring(L, name)接下来就是善后工作了。注意，_LOADED[name]被设置为true。*/  lua_getfield(L, 2, name);  if (lua_touserdata(L, -1) == sentinel) {   /* module did not set a value? */    lua_pushboolean(L, 1);  /* use true as result */    lua_pushvalue(L, -1);  /* extra copy to be returned */    lua_setfield(L, 2, name);  /* _LOADED[name] = true */  }  return 1;}

/*段1*/static int loader_preload (lua_State *L) {/*取得0x00395158:lua_pushstring(L, name);*/  const char *name = luaL_checkstring(L, 1);/*0x00395168:LUA_ENVIRONINDEX, "preload"*/  lua_getfield(L, LUA_ENVIRONINDEX, "preload");  if (!lua_istable(L, -1))    luaL_error(L, LUA_QL("package.preload") " must be a table");/*0x00395178:从0x00395168LUA_ENVIRONINDEX, "preload"表里，读取name的字段*/  lua_getfield(L, -1, name);/* 如果是自定义的，则没找到,压入字符串，供上层判断*/  if (lua_isnil(L, -1))  /* not found? */    lua_pushfstring(L, "\n\tno field package.preload['%s']", name);  return 1;}

/*段2*/static int loader_Lua (lua_State *L) {  const char *filename;  const char *name = luaL_checkstring(L, 1);/*查找路径的规则。如果想知道具体没必要细跟。可以设置一个找不到模块名，查看返回的错误信息(带有所有路径名的搜索)即可。*/  filename = findfile(L, name, "path");  if (filename == NULL) return 1;  /* library not found in this path *//*luaL_loadfile很熟悉了*/  if (luaL_loadfile(L, filename) != 0)    loaderror(L, filename);  return 1;  /* library loaded successfully */}