lua_State 是什么东西
lua 5.1
lua_State L = luaL_newstate();
在使用lua API 时第一步经常是上面这句话,那么 lua_State 到底是什么东西?
先看看下面对 luaL_newstate() 的实现
// luaxlib.h
LUALIB_API lua_State *(luaL_newstate) (void);
// luaxlib.c
LUALIB_API lua_State *luaL_newstate (void) {
lua_State *L = lua_newstate(l_alloc, NULL);
if (L) lua_atpanic(L, &panic);
return L;
}
继续看 luaL_newstate 是怎么创建 lua_State 的
LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud) {
int i;
lua_State *L;
global_State *g;
void *l = (*f)(ud, NULL, 0, state_size(LG));
if (l == NULL) return NULL;
L = tostate(l);
...
return L;
}
可见在调用 luaL_newstate 时创建的是 LG 类型的对象,继续看 LG 的定义。
LG 定义
/*
** Main thread combines a thread state and the global state
*/
typedef struct LG {
lua_State l;
global_State g;
} LG;
lua 5.2 之后
/*
** thread state + extra space
*/
typedef struct LX {
lu_byte extra_[LUA_EXTRASPACE];
lua_State l;
} LX;
/*
** Main thread combines a thread state and the global state
*/
typedef struct LG {
LX l;
global_State g;
} LG;
由此可见 LG 是一个包含了线程状态即 lua_State 和 全局状态的结构体。
即,我们在调用 luaL_newstate 是创建了 LG,给我们返回的是 LG 的属性 lua_State
而 global_State 对我们来说是不可见的。
一下是对 lua_State 和 global_State 的定义
/*
** `per thread' state
*/
struct lua_State {
CommonHeader;
lu_byte status;
StkId top; /* first free slot in the stack */
StkId base; /* base of current function */
global_State *l_G;
CallInfo *ci; /* call info for current function */
const Instruction *savedpc; /* `savedpc' of current function */
StkId stack_last; /* last free slot in the stack */
StkId stack; /* stack base */
CallInfo *end_ci; /* points after end of ci array*/
CallInfo *base_ci; /* array of CallInfo's */
int stacksize;
int size_ci; /* size of array `base_ci' */
unsigned short nCcalls; /* number of nested C calls */
unsigned short baseCcalls; /* nested C calls when resuming coroutine */
lu_byte hookmask;
lu_byte allowhook;
int basehookcount;
int hookcount;
lua_Hook hook;
TValue l_gt; /* table of globals */
TValue env; /* temporary place for environments */
GCObject *openupval; /* list of open upvalues in this stack */
GCObject *gclist;
struct lua_longjmp *errorJmp; /* current error recover point */
ptrdiff_t errfunc; /* current error handling function (stack index) */
};
/*
** `global state', shared by all threads of this state
*/
typedef struct global_State {
stringtable strt; /* hash table for strings */
lua_Alloc frealloc; /* function to reallocate memory */
void *ud; /* auxiliary data to `frealloc' */
lu_byte currentwhite;
lu_byte gcstate; /* state of garbage collector */
int sweepstrgc; /* position of sweep in `strt' */
GCObject *rootgc; /* list of all collectable objects */
GCObject **sweepgc; /* position of sweep in `rootgc' */
GCObject *gray; /* list of gray objects */
GCObject *grayagain; /* list of objects to be traversed atomically */
GCObject *weak; /* list of weak tables (to be cleared) */
GCObject *tmudata; /* last element of list of userdata to be GC */
Mbuffer buff; /* temporary buffer for string concatentation */
lu_mem GCthreshold;
lu_mem totalbytes; /* number of bytes currently allocated */
lu_mem estimate; /* an estimate of number of bytes actually in use */
lu_mem gcdept; /* how much GC is `behind schedule' */
int gcpause; /* size of pause between successive GCs */
int gcstepmul; /* GC `granularity' */
lua_CFunction panic; /* to be called in unprotected errors */
TValue l_registry;
struct lua_State *mainthread;
UpVal uvhead; /* head of double-linked list of all open upvalues */
struct Table *mt[NUM_TAGS]; /* metatables for basic types */
TString *tmname[TM_N]; /* array with tag-method names */
} global_State;