Lua源码学习-lapi.c

/*
** $Id: lapi.c,v 2.257 2015/11/02 18:48:07 roberto Exp $
** Lua API
** See Copyright Notice in lua.h
*/

#define lapi_c
#define LUA_CORE

#include "lprefix.h"

#include <stdarg.h>
#include <string.h>

#include "lua.h"

#include "lapi.h"
#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"
#include "lundump.h"
#include "lvm.h"

/* 使用了字符串自动连接的特性 */
const char lua_ident[] =
  "$LuaVersion: " LUA_COPYRIGHT " $"
  "$LuaAuthors: " LUA_AUTHORS " $";

/* value at a non-valid index */
#define NONVALIDVALUE        cast(TValue *, luaO_nilobject)

/* corresponding(一致) test */
#define isvalid(o)    ((o) != luaO_nilobject)

/*
* test for pseudo(伪) index
* 看LUA_REGISTRYINDEX的宏定义便一目了然
*/
#define ispseudo(i)        ((i) <= LUA_REGISTRYINDEX)

/* test for upvalue */
#define isupvalue(i)        ((i) < LUA_REGISTRYINDEX)

/* test for valid but not pseudo index */
#define isstackindex(i, o)    (isvalid(o) && !ispseudo(i))

#define api_checkvalidindex(l,o)  api_check(l, isvalid(o), "invalid index")

#define api_checkstackindex(l, i, o)  \
    api_check(l, isstackindex(i, o), "index not in the stack")

/*
* 按索引值范围解析出对应的slot
* 不同于C的地址索引从0开始，Lua的从1开始
* 可以从这个函数看出一些Lua的设计点
*/
static TValue *index2addr (lua_State *L, int idx) {
  CallInfo *ci = L->ci;
  if (idx > 0) {
    TValue *o = ci->func + idx;  /* idx>=1可以推断出ci->func保存了被调用的函数指针 */

    /* 下面这个判断，按照正常的来说不应该是idx <= ((ci->top - (ci->func + 1)) + 1)么，
     ** 为什么没有加1呢，拿笔纸出来画一下就知道top指针可能指向类似数值最后一个元素的下一个元素了哦
     ** ci->func+1指向第一个数据类的slot, ci->func则是保存了被调用的函数的指针？
    */
    api_check(L, idx <= ci->top - (ci->func + 1), "unacceptable index");

    //这里说明了L->top这个是一个阈值，实际上不可解析
    if (o >= L->top) return NONVALIDVALUE;
    else return o;
  } else if (!ispseudo(idx)) {  /* negative index  idx>LUA_REGISTRYINDEX pseudo:伪装，匿名 */
      /* 这里用的是L->top和上面的ci->top不一样哦 */
    api_check(L, idx != 0 && -idx <= L->top - (ci->func + 1), "invalid index");
    return L->top + idx;
  } else if (idx == LUA_REGISTRYINDEX) {  //预留给C的一个特定slot(注册表(全局表？))
    return &G(L)->l_registry;
   } else {  /* upvalues */
    idx = LUA_REGISTRYINDEX - idx;
    api_check(L, idx <= MAXUPVAL + 1, "upvalue index too large");
    if (ttislcf(ci->func))  /* light C function? */
      return NONVALIDVALUE;  /* it has no upvalues */
    else {
      CClosure *func = clCvalue(ci->func);
      return (idx <= func->nupvalues) ? &func->upvalue[idx-1] : NONVALIDVALUE;
    }
  }
}

/*
** to be called by 'lua_checkstack' in protected mode, to grow stack
** capturing memory errors
** 在不超过堆栈尺寸限制的情况下修改堆栈尺寸信息
*/
static void growstack (lua_State *L, void *ud) {
  int size = *(int *)ud;
  luaD_growstack(L, size);
}

/* 调整堆栈的大小确保空闲的slot数量>=n */
LUA_API int lua_checkstack (lua_State *L, int n) {
  int res;
  CallInfo *ci = L->ci;
  lua_lock(L);
  api_check(L, n >= 0, "negative 'n'");
  if (L->stack_last - L->top > n)  /* stack large enough? */
    res = 1;  /* yes; check is OK */
  else {  /* no; need to grow stack */
    int inuse = cast_int(L->top - L->stack) + EXTRA_STACK;
    if (inuse + n > LUAI_MAXSTACK) /* n值太大了 */
    //if (inuse > LUAI_MAXSTACK - n)  /* can grow without overflow? */
      res = 0;  /* no */
    else  /* try to grow stack */
      res = (luaD_rawrunprotected(L, &growstack, &n) == LUA_OK);
  }
  if (res && ci->top < L->top + n)
    ci->top = L->top + n;  /* adjust frame top */
  lua_unlock(L);
  return res;
}

/*
 * 从堆栈from移动N个元素到to上
 * form,to必须指向同一个虚拟机
*/
LUA_API void lua_xmove (lua_State *from, lua_State *to, int n) {
  int i;
  if (from == to) return;
  lua_lock(to);
  api_checknelems(from, n);
  api_check(from, G(from) == G(to), "moving among independent states");
  api_check(from, to->ci->top - to->top >= n, "stack overflow");
  from->top -= n;
  for (i = 0; i < n; i++) {
    setobj2s(to, to->top, from->top + i);
    to->top++;  /* stack already checked by previous 'api_check' */
  }
  lua_unlock(to);
}

/*
 * 设置"异常"处理句柄
 * 这里返回了可能的旧句柄，这是一个好习惯
*/
LUA_API lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf) {
  lua_CFunction old;
  lua_lock(L);
  old = G(L)->panic;
  G(L)->panic = panicf;
  lua_unlock(L);
  return old;
}

/* 返回全局的版本器或自己的版本器 */
LUA_API const lua_Number *lua_version (lua_State *L) {
  static const lua_Number version = LUA_VERSION_NUM;
  if (L == NULL)
        return &version;    /* 避免静态库的N份的链接问题，这里返回地址，用于调用者对比 */
  else
        return G(L)->version;
}

/*
** basic stack manipulation
*/

/*
** convert an acceptable stack index into an absolute index
** 拿笔和纸划一下堆栈图就知道了，这是求有效的idx
*/
LUA_API int lua_absindex (lua_State *L, int idx) {
  return (idx > 0 || ispseudo(idx))
         ? idx
         : cast_int(L->top - L->ci->func) + idx;
}

/* 求栈内元素个数
 * 仔细揣摩下这里的top和L->ci->func+1
 * L->ci->func这个slot存放的是回跳地址么？(ps:本栈结束后，上一个栈的基地址),top:又指代什么
 * 普通的[n,m]区间的slot个数计算公式是m-n+1,这里是m-n-1,差了2，一头一尾
*/
LUA_API int lua_gettop (lua_State *L) {
  return cast_int(L->top - (L->ci->func + 1));
}

/* 调整栈顶指针，扩大(填nil)或缩小栈
** idx>=0表示留下多少个slot,
** <0表示,保留到哪一个元素，-1：表示保留到最后一个元素，等于做无用功，-2：表示保留到倒数第二个元素，等于剔除一个元素,依次类推
*/
LUA_API void lua_settop (lua_State *L, int idx) {
  StkId func = L->ci->func;
  lua_lock(L);
  if (idx >= 0) {
    api_check(L, idx <= L->stack_last - (func + 1), "new top too large");
    while (L->top < (func + 1) + idx)    /* 补充扩充的slot,填nil */
      setnilvalue(L->top++);
    L->top = (func + 1) + idx;
  } else {
    api_check(L, -(idx+1) <= (L->top - (func + 1)), "invalid new top");
    L->top += idx+1;  /* 'subtract' index (index is negative) */
  }
  lua_unlock(L);
}

/*
** Reverse the stack segment from 'from' to 'to'
** (auxiliary(辅助) to 'lua_rotate(旋转)')
** 交换slot中的值
*/
static void reverse (lua_State *L, StkId from, StkId to) {
  for (; from < to; from++, to--) {
    TValue temp;
    setobj(L, &temp, from);
    setobjs2s(L, from, to);
    setobj2s(L, to, &temp);
  }
}

/*
** Let x = AB, where A is a prefix of length 'n'. Then,
** rotate(旋转) x n == BA. But BA == (A^r . B^r)^r.
*/
LUA_API void lua_rotate (lua_State *L, int idx, int n) {
  StkId p, t, m;
  lua_lock(L);
  t = L->top - 1;  /* end of stack segment being rotated */
  p = index2addr(L, idx);  /* start of segment */
  api_checkstackindex(L, idx, p);
  api_check(L, (n >= 0 ? n : -n) <= (t - p + 1), "invalid 'n'");
  m = (n >= 0 ? t - n : p - n - 1);  /* end of prefix */
  reverse(L, p, m);  /* reverse the prefix with length 'n' */
  reverse(L, m + 1, t);  /* reverse the suffix */
  reverse(L, p, t);  /* reverse the entire segment */
  lua_unlock(L);
}

LUA_API void lua_copy (lua_State *L, int fromidx, int toidx) {
  TValue *fr, *to;
  lua_lock(L);
  fr = index2addr(L, fromidx);
  to = index2addr(L, toidx);
  api_checkvalidindex(L, to);
  setobj(L, to, fr);
  if (isupvalue(toidx))  /* function upvalue? */
    luaC_barrier(L, clCvalue(L->ci->func), fr);
  /* LUA_REGISTRYINDEX does not need gc barrier
     (collector revisits it before finishing collection) */
  lua_unlock(L);
}

//将idx指定的slot中的值CP一份到栈顶，并且修正L->top指针,而没有修正L->ci->top指针
LUA_API void lua_pushvalue (lua_State *L, int idx) {
  lua_lock(L);
  setobj2s(L, L->top, index2addr(L, idx));
  api_incr_top(L);
  lua_unlock(L);
}

/*
** access functions (stack -> C)
*/

//仅考虑bit[0, 3]的类型，不考虑 [4,5]的类型
//eg:数字类型，而不具体区分是double还是int
LUA_API int lua_type (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  return (isvalid(o) ? ttnov(o) : LUA_TNONE);
}

/* 返回大类型名(number而不是interget) */
LUA_API const char *lua_typename (lua_State *L, int t) {
  UNUSED(L);
  api_check(L, LUA_TNONE <= t && t < LUA_NUMTAGS, "invalid tag");
  return ttypename(t);
}

LUA_API int lua_iscfunction (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  return (ttislcf(o) || (ttisCclosure(o)));
}

LUA_API int lua_isinteger (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  return ttisinteger(o);
}

LUA_API int lua_isnumber (lua_State *L, int idx) {
  lua_Number n;
  const TValue *o = index2addr(L, idx);
  return tonumber(o, &n);
}

LUA_API int lua_isstring (lua_State *L, int idx) {
  const TValue *o = index2addr(L, idx);
  return (ttisstring(o) || cvt2str(o));
}

LUA_API int lua_isuserdata (lua_State *L, int idx) {
  const TValue *o = index2addr(L, idx);
  return (ttisfulluserdata(o) || ttislightuserdata(o));
}

/* 不用元方法的裸比 */
LUA_API int lua_rawequal (lua_State *L, int index1, int index2) {
  StkId o1 = index2addr(L, index1);
  StkId o2 = index2addr(L, index2);
  return (isvalid(o1) && isvalid(o2)) ? luaV_rawequalobj(o1, o2) : 0;
}

/* 进行某种运算 */
LUA_API void lua_arith (lua_State *L, int op) {
  lua_lock(L);
  if (op != LUA_OPUNM && op != LUA_OPBNOT)
    api_checknelems(L, 2);  /* all other operations expect two operands */
  else {  /* for unary operations, add fake 2nd operand */
    api_checknelems(L, 1);
    setobjs2s(L, L->top, L->top - 1);    /* 将最后一个slot元素拷贝一份到栈顶，并++top，以便形成2个参数 */
    api_incr_top(L);
  }
  
  /* 
   ** first operand at top - 2, second at top - 1; result go to top - 2 
   ** 仔细仔细读上面的这句话，可以看出val1+val2,运行完毕后，保留了结果，弹出了所有的操作数
   ** 一般的计算机都会这样干哦？
   */
  luaO_arith(L, op, L->top - 2, L->top - 1, L->top - 2);
  L->top--;  /* remove second operand */
  
  lua_unlock(L);
}

LUA_API int lua_compare (lua_State *L, int index1, int index2, int op) {
  StkId o1, o2;
  int i = 0;
  lua_lock(L);  /* may call tag method */
  o1 = index2addr(L, index1);
  o2 = index2addr(L, index2);
  if (isvalid(o1) && isvalid(o2)) {
    switch (op) {
      case LUA_OPEQ: i = luaV_equalobj(L, o1, o2); break;
      case LUA_OPLT: i = luaV_lessthan(L, o1, o2); break;
      case LUA_OPLE: i = luaV_lessequal(L, o1, o2); break;
      default: api_check(L, 0, "invalid option");
    }
  }
  lua_unlock(L);
  return i;
}

/* 会被 tonumber()函数调用到哦 */
LUA_API size_t lua_stringtonumber (lua_State *L, const char *s) {
  size_t sz = luaO_str2num(s, L->top);
  if (sz != 0) // 这里要先判断下转换结果
    api_incr_top(L);
  return sz;
}

LUA_API lua_Number lua_tonumberx (lua_State *L, int idx, int *pisnum) {
  lua_Number n;
  const TValue *o = index2addr(L, idx);
  int isnum = tonumber(o, &n);
  if (!isnum)
    n = 0;  /* call to 'tonumber' may change 'n' even if it fails */
  if (pisnum) *pisnum = isnum;
  return n;
}

//将idx指定的参数转换为整数，
//pisnum:转换是否成功的标志位
LUA_API lua_Integer lua_tointegerx (lua_State *L, int idx, int *pisnum) {
  lua_Integer res;
  const TValue *o = index2addr(L, idx);
  int isnum = tointeger(o, &res);
  if (!isnum)
    res = 0;  /* call to 'tointeger' may change 'n' even if it fails */
  if (pisnum) *pisnum = isnum;
  return res;
}

LUA_API int lua_toboolean (lua_State *L, int idx) {
  const TValue *o = index2addr(L, idx);
  return !l_isfalse(o);
}

LUA_API const char *lua_tolstring (lua_State *L, int idx, size_t *len) {
  StkId o = index2addr(L, idx);
  if (!ttisstring(o)) {
    if (!cvt2str(o)) {  /* not convertible? */
      if (len != NULL) *len = 0;
      return NULL;
    }
    lua_lock(L);  /* 'luaO_tostring' may create a new string */
    luaC_checkGC(L);
    o = index2addr(L, idx);  /* previous call may reallocate the stack */
    luaO_tostring(L, o);
    lua_unlock(L);
  }
  if (len != NULL)
    *len = vslen(o);
  return svalue(o);
}

/* 计算字符串,userdata,table的长度 */
LUA_API size_t lua_rawlen (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  switch (ttype(o)) {
    case LUA_TSHRSTR: return tsvalue(o)->shrlen;
    case LUA_TLNGSTR: return tsvalue(o)->u.lnglen;
    case LUA_TUSERDATA: return uvalue(o)->len;
    case LUA_TTABLE: return luaH_getn(hvalue(o));
    default: return 0;
  }
}

LUA_API lua_CFunction lua_tocfunction (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  if (ttislcf(o)) return fvalue(o);        /* light C function */
  else if (ttisCclosure(o))                /* C closure */
    return clCvalue(o)->f;
  else return NULL;  /* not a C function */
}

LUA_API void *lua_touserdata (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  switch (ttnov(o)) {
    case LUA_TUSERDATA: return getudatamem(uvalue(o));
    case LUA_TLIGHTUSERDATA: return pvalue(o);-
    default: return NULL;
  }
}

LUA_API lua_State *lua_tothread (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  return (!ttisthread(o)) ? NULL : thvalue(o);
}

LUA_API const void *lua_topointer (lua_State *L, int idx) {
  StkId o = index2addr(L, idx);
  switch (ttype(o)) {
    case LUA_TTABLE: return hvalue(o);
    case LUA_TLCL: return clLvalue(o);
    case LUA_TCCL: return clCvalue(o);
    case LUA_TLCF: return cast(void *, cast(size_t, fvalue(o)));
    case LUA_TTHREAD: return thvalue(o);
    case LUA_TUSERDATA: return getudatamem(uvalue(o));
    case LUA_TLIGHTUSERDATA: return pvalue(o);
    default: return NULL;
  }
}

/*
** push functions (C -> stack)
*/

LUA_API void lua_pushnil (lua_State *L) {
  lua_lock(L);

  /* 看的出这里的L->top指向下一个可用的slot,而不是上一个被填满的slot，这边要适应
   * 压入值后，要手动top++，下同。
   */
  setnilvalue(L->top);
  api_incr_top(L);
  
  lua_unlock(L);
}

LUA_API void lua_pushnumber (lua_State *L, lua_Number n) {
  lua_lock(L);
  setfltvalue(L->top, n);
  api_incr_top(L);
  lua_unlock(L);
}

LUA_API void lua_pushinteger (lua_State *L, lua_Integer n) {
  lua_lock(L);
  setivalue(L->top, n);
  api_incr_top(L);
  lua_unlock(L);
}

/*
** Pushes on the stack a string with given length. Avoid using 's' when
** 'len' == 0 (as 's' can be NULL in that case), due to later use of
** 'memcmp' and 'memcpy'.
*/
LUA_API const char *lua_pushlstring (lua_State *L, const char *s, size_t len) {
  TString *ts;
  lua_lock(L);
  luaC_checkGC(L);
  ts = (len == 0) ? luaS_new(L, "") : luaS_newlstr(L, s, len);
  setsvalue2s(L, L->top, ts);
  api_incr_top(L);
  lua_unlock(L);
  return getstr(ts);
}

/* 将C的s字符串转换为String，压入栈顶 */
LUA_API const char *lua_pushstring (lua_State *L, const char *s) {
  lua_lock(L);
  if (s == NULL)
    setnilvalue(L->top);
  else {
    TString *ts;
    luaC_checkGC(L);
    ts = luaS_new(L, s);
    setsvalue2s(L, L->top, ts);
    s = getstr(ts);  /* internal copy's address */
  }
  api_incr_top(L);
  lua_unlock(L);
  return s;
}

LUA_API const char *lua_pushvfstring (lua_State *L, const char *fmt,
                                      va_list argp) {
  const char *ret;
  lua_lock(L);
  luaC_checkGC(L);
  ret = luaO_pushvfstring(L, fmt, argp);
  lua_unlock(L);
  return ret;
}

LUA_API const char *lua_pushfstring (lua_State *L, const char *fmt, ...) {
  const char *ret;
  va_list argp;
  lua_lock(L);
  luaC_checkGC(L);
  va_start(argp, fmt);
  ret = luaO_pushvfstring(L, fmt, argp);
  va_end(argp);
  lua_unlock(L);
  return ret;
}

//创建一个闭包
//若上值个数为0，则创建一个简单的闭包即可
//若有N个上值，则创建一个闭包，将栈顶上的上值填入闭包中，最后弹出上值，压入新构建的闭包
LUA_API void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n) {
  lua_lock(L);
  if (n == 0) { //简单的CFunction
    setfvalue(L->top, fn);
  }
  else {
    CClosure *cl;
    api_checknelems(L, n);
    api_check(L, n <= MAXUPVAL, "upvalue index too large");
    luaC_checkGC(L);
    cl = luaF_newCclosure(L, n);
    cl->f = fn;
    L->top -= n;
    while (n--) {
      setobj2n(L, &cl->upvalue[n], L->top + n); //复制上值
      /* does not need barrier because closure is white */
    }
    setclCvalue(L, L->top, cl); //压入构建好的闭包到栈顶
  }
  api_incr_top(L);
  lua_unlock(L);
}

LUA_API void lua_pushboolean (lua_State *L, int b) {
  lua_lock(L);
  setbvalue(L->top, (b != 0));  /* ensure that true is 1 */
  api_incr_top(L);
  lua_unlock(L);
}

LUA_API void lua_pushlightuserdata (lua_State *L, void *p) {
  lua_lock(L);
  setpvalue(L->top, p);
  api_incr_top(L);
  lua_unlock(L);
}

LUA_API int lua_pushthread (lua_State *L) {
  lua_lock(L);
  setthvalue(L, L->top, L);
  api_incr_top(L);
  lua_unlock(L);
  return (G(L)->mainthread == L);
}

/*
** get functions (Lua -> stack)
*/

static int auxgetstr (lua_State *L, const TValue *t, const char *k) {
  const TValue *aux;

  /* 将外部的const chant *k指针转换为Lua内部的TString */
  TString *str = luaS_new(L, k);
  
  if (luaV_fastget(L, t, str, aux, luaH_getstr)) {    /* 在table中找到了key的值 */
    setobj2s(L, L->top, aux);
    api_incr_top(L);
  } else {
    setsvalue2s(L, L->top, str);
    api_incr_top(L);
    luaV_finishget(L, t, L->top - 1, L->top - 1, aux);
  }
  lua_unlock(L);
  return ttnov(L->top - 1);
}

LUA_API int lua_getglobal (lua_State *L, const char *name) {
  Table *reg = hvalue(&G(L)->l_registry);
  lua_lock(L);
  return auxgetstr(L, luaH_getint(reg, LUA_RIDX_GLOBALS), name);
}

/* 查找由idx指定的table中L->top-1指定的key的val值，并把结果放到L->top-1上 */
LUA_API int lua_gettable (lua_State *L, int idx) {
  StkId t;
  lua_lock(L);
  t = index2addr(L, idx);
  luaV_gettable(L, t, L->top - 1, L->top - 1);
  lua_unlock(L);
  return ttnov(L->top - 1);
}

/* 
 * 获取位于idx指定的表的key域的值(返回到栈顶上) 
 * top = T(idx)[key]
 */
LUA_API int lua_getfield (lua_State *L, int idx, const char *k) {
  lua_lock(L);
  return auxgetstr(L, index2addr(L, idx), k);
}

//上面函数的type(key)==int的版
LUA_API int lua_geti (lua_State *L, int idx, lua_Integer n) {
  StkId t;
  const TValue *aux;
  lua_lock(L);
  t = index2addr(L, idx);
  if (luaV_fastget(L, t, n, aux, luaH_getint)) {
    setobj2s(L, L->top, aux);
    api_incr_top(L);
  }
  else {
    setivalue(L->top, n);
    api_incr_top(L);
    luaV_finishget(L, t, L->top - 1, L->top - 1, aux);
  }
  lua_unlock(L);
  return ttnov(L->top - 1);
}

LUA_API int lua_rawget (lua_State *L, int idx) {
  StkId t;
  lua_lock(L);
  t = index2addr(L, idx);
  api_check(L, ttistable(t), "table expected");
  setobj2s(L, L->top - 1, luaH_get(hvalue(t), L->top - 1));
  lua_unlock(L);
  return ttnov(L->top - 1);
}

//提取idx指定的表的key==n的值
LUA_API int lua_rawgeti (lua_State *L, int idx, lua_Integer n) {
  StkId t;
  lua_lock(L);
  t = index2addr(L, idx);
  api_check(L, ttistable(t), "table expected");
  setobj2s(L, L->top, luaH_getint(hvalue(t), n));
  api_incr_top(L);
  lua_unlock(L);
  return ttnov(L->top - 1);
}

//get light userdata
LUA_API int lua_rawgetp (lua_State *L, int idx, const void *p) {
  StkId t;
  TValue k;
  lua_lock(L);
  t = index2addr(L, idx);
  api_check(L, ttistable(t), "table expected");
  setpvalue(&k, cast(void *, p));
  setobj2s(L, L->top, luaH_get(hvalue(t), &k));
  api_incr_top(L);
  lua_unlock(L);
  return ttnov(L->top - 1);
}

/* 
** 构建一个narray,nrec的表
** 之后压入栈顶
*/
LUA_API void lua_createtable (lua_State *L, int narray, int nrec) {
  Table *t;
  lua_lock(L);
  luaC_checkGC(L);
  t = luaH_new(L);    /* 先构建一个zero的表 */
  sethvalue(L, L->top, t);
  api_incr_top(L);
  if (narray > 0 || nrec > 0)
    luaH_resize(L, t, narray, nrec);    /* 这里再扩展array或rec区域 */
  lua_unlock(L);
}

//提取Table, UserData等的元表
LUA_API int lua_getmetatable (lua_State *L, int objindex) {
  const TValue *obj;
  Table *mt;
  int res = 0;
  lua_lock(L);
  obj = index2addr(L, objindex);
  switch (ttnov(obj)) {
    case LUA_TTABLE:
      mt = hvalue(obj)->metatable;
      break;
    case LUA_TUSERDATA:
      mt = uvalue(obj)->metatable;
      break;
    default:    /* 这里看的出，其它类型的，直接读全局表 */
      mt = G(L)->mt[ttnov(obj)];
      break;
  }
  if (mt != NULL) {
    sethvalue(L, L->top, mt);  //将结果压栈
    api_incr_top(L);
    res = 1;
  }
  lua_unlock(L);
  return res;
}

LUA_API int lua_getuservalue (lua_State *L, int idx) {
  StkId o;
  lua_lock(L);
  o = index2addr(L, idx);
  api_check(L, ttisfulluserdata(o), "full userdata expected");
  getuservalue(L, uvalue(o), L->top);
  api_incr_top(L);
  lua_unlock(L);
  return ttnov(L->top - 1);
}

/*
** set functions (stack -> Lua)
**
** t[k] = value at the top of the stack (where 'k' is a string)
** 看代码，值已经放到L->top-1的slot栈位置
*/
static void auxsetstr (lua_State *L, const TValue *t, const char *k) {
  const TValue *aux;
  
  TString *str = luaS_new(L, k);    /* 这里将k指向的字符串先转为内部的TString */
  
  api_checknelems(L, 1);
  if (luaV_fastset(L, t, str, aux, luaH_getstr, L->top - 1))
    L->top--;  /* pop value */
  else {
    setsvalue2s(L, L->top, str);  /* push 'str' (to make it a TValue) */
    api_incr_top(L);

    luaV_finishset(L, t, L->top - 1, L->top - 2, aux);
    L->top -= 2;  /* pop value and key */
  }
  lua_unlock(L);  /* lock done by caller */
}

/* 类似上面的函数，不过表是全局注册表了 */
LUA_API void lua_setglobal (lua_State *L, const char *name) {
  Table *reg = hvalue(&G(L)->l_registry);
  lua_lock(L);  /* unlock done in 'auxsetstr' */
  auxsetstr(L, luaH_getint(reg, LUA_RIDX_GLOBALS), name);
}

/* key，value已放到了栈顶对应的slot，这里idx来确定表 */
LUA_API void lua_settable (lua_State *L, int idx) {
  StkId t;
  lua_lock(L);
  api_checknelems(L, 2);
  t = index2addr(L, idx);
  luaV_settable(L, t, L->top - 2, L->top - 1);
  L->top -= 2;  /* pop index and value */
  lua_unlock(L);
}

//idx["k"] = top,之后将top弹出栈,表由idx指定
LUA_API void lua_setfield (lua_State *L, int idx, const char *k) {
  lua_lock(L);  /* unlock done in 'auxsetstr' */
  auxsetstr(L, index2addr(L, idx), k);
}

//idx[n] = top,之后将top弹出栈
LUA_API void lua_seti (lua_State *L, int idx, lua_Integer n) {
  StkId t;
  const TValue *aux;
  lua_lock(L);
  api_checknelems(L, 1);
  t = index2addr(L, idx);
  if (luaV_fastset(L, t, n, aux, luaH_getint, L->top - 1)) {
    L->top--;  /* pop value */
  } else {
    setivalue(L->top, n);
    api_incr_top(L);
    luaV_finishset(L, t, L->top - 1, L->top - 2, aux);
    L->top -= 2;  /* pop value and key */
  }
  lua_unlock(L);
}

//将idx指定的tbl进行tbl[top-2] = *(top-1)
LUA_API void lua_rawset (lua_State *L, int idx) {
  StkId o;
  TValue *slot;
  lua_lock(L);
  api_checknelems(L, 2);
  o = index2addr(L, idx);
  api_check(L, ttistable(o), "table expected");
  slot = luaH_set(L, hvalue(o), L->top - 2);
  setobj2t(L, slot, L->top - 1);
  invalidateTMcache(hvalue(o));
  luaC_barrierback(L, hvalue(o), L->top-1);
  L->top -= 2;
  lua_unlock(L);
}

//idx'Table [n] = top
LUA_API void lua_rawseti (lua_State *L, int idx, lua_Integer n) {
  StkId o;
  lua_lock(L);
  api_checknelems(L, 1);
  o = index2addr(L, idx);
  api_check(L, ttistable(o), "table expected");
  luaH_setint(L, hvalue(o), n, L->top - 1);
  luaC_barrierback(L, hvalue(o), L->top-1);
  L->top--;
  lua_unlock(L);
}

//set light userdata
LUA_API void lua_rawsetp (lua_State *L, int idx, const void *p) {
  StkId o;
  TValue k, *slot;
  lua_lock(L);
  api_checknelems(L, 1);
  o = index2addr(L, idx);
  api_check(L, ttistable(o), "table expected");
  setpvalue(&k, cast(void *, p));
  slot = luaH_set(L, hvalue(o), &k);
  setobj2t(L, slot, L->top - 1);
  luaC_barrierback(L, hvalue(o), L->top - 1);
  L->top--;
  lua_unlock(L);
}

/*
** statck[top]->table.meatetable = objindex
** 仔细看完这个函数，switch中三种情况的处理
** statck[objindex].metatable = statck[top]
*/
LUA_API int lua_setmetatable (lua_State *L, int objindex) {
  TValue *obj;
  Table *mt;
  lua_lock(L);
  api_checknelems(L, 1);
  
  if (ttisnil(L->top - 1))    /* 空值相当于取消原表 */
    mt = NULL;
  else {
    api_check(L, ttistable(L->top - 1), "table expected");    /* 这里可以看到，非空时，必须是张表 */
    mt = hvalue(L->top - 1);
  }
  
  obj = index2addr(L, objindex);    /* 确定被设置原表的对象 */
  switch (ttnov(obj)) {
    case LUA_TTABLE: {
      hvalue(obj)->metatable = mt;
      if (mt) {
        luaC_objbarrier(L, gcvalue(obj), mt);
        luaC_checkfinalizer(L, gcvalue(obj), mt);
      }
      break;
    }
    case LUA_TUSERDATA: {
      uvalue(obj)->metatable = mt;
      if (mt) {
        luaC_objbarrier(L, uvalue(obj), mt);
        luaC_checkfinalizer(L, gcvalue(obj), mt);
      }
      break;
    }
    default: {
      G(L)->mt[ttnov(obj)] = mt; /* 厉害了哦,这里可以对基础类型的原表进行覆盖处理,没必要，必要进行此操作吧 */
      break;
    }
  }
  L->top--;
  lua_unlock(L);
  return 1;    /* 这里返回1有啥意义？ */
}

/* statck[idx] = top */
LUA_API void lua_setuservalue (lua_State *L, int idx) {
  StkId o;
  lua_lock(L);
  api_checknelems(L, 1);
  o = index2addr(L, idx);
  api_check(L, ttisfulluserdata(o), "full userdata expected");
  setuservalue(L, uvalue(o), L->top - 1);
  luaC_barrier(L, gcvalue(o), L->top - 1);
  L->top--;
  lua_unlock(L);
}

/*
** 'load' and 'call' functions (run Lua code)
*/

#define checkresults(L,na,nr) \
     api_check(L, (nr) == LUA_MULTRET || (L->ci->top - L->top >= (nr) - (na)), \
    "results from function overflow current stack size")

/* KEY-FUN
 ** 多看看此函数，目前还没有看懂 2020/05/13
*/
LUA_API void lua_callk (lua_State *L, int nargs, int nresults,
                        lua_KContext ctx, lua_KFunction k) {
  StkId func;
  lua_lock(L);    /* 考虑下：上面定义变量和这一行的lock调用的前后顺序调换下位置对性能而言有啥区别？ */
  
  api_check(L, k == NULL || !isLua(L->ci),
    "cannot use continuations inside hooks");
  api_checknelems(L, nargs+1);
  api_check(L, L->status == LUA_OK, "cannot do calls on non-normal thread");
  checkresults(L, nargs, nresults);

  /* 函数指针在这里,另外看的出参数放到了函数指针的"上面"         */
  func = L->top - (nargs+1);
  
  if (k != NULL && L->nny == 0) {  /* need to prepare continuation? */
    L->ci->u.c.k = k;  /* save continuation */
    L->ci->u.c.ctx = ctx;  /* save context */
    luaD_call(L, func, nresults);  /* do the call */
  }
  else  /* no continuation or no yieldable */
    luaD_callnoyield(L, func, nresults);  /* just do the call */
  
  adjustresults(L, nresults);
  lua_unlock(L);
}

/*
** Execute a protected call.
*/
struct CallS {  /* data to 'f_call' */
  StkId func;
  int nresults;
};

static void f_call (lua_State *L, void *ud) {
  struct CallS *c = cast(struct CallS *, ud);
  luaD_callnoyield(L, c->func, c->nresults);
}

/*
 ** 带保护模式下调用函数？，看不懂，后面遇到了再多看几次吧
*/
LUA_API int lua_pcallk (lua_State *L, int nargs, int nresults, int errfunc,
                        lua_KContext ctx, lua_KFunction k) {
  struct CallS c;
  int status;
  ptrdiff_t func;
  lua_lock(L);
  api_check(L, k == NULL || !isLua(L->ci),
    "cannot use continuations inside hooks");
  api_checknelems(L, nargs+1);
  api_check(L, L->status == LUA_OK, "cannot do calls on non-normal thread");
  checkresults(L, nargs, nresults);
  if (errfunc == 0)
    func = 0;
  else {
    StkId o = index2addr(L, errfunc);
    api_checkstackindex(L, errfunc, o);
    func = savestack(L, o);
  }
  c.func = L->top - (nargs+1);  /* function to be called */
  if (k == NULL || L->nny > 0) {  /* no continuation or no yieldable? */
    c.nresults = nresults;  /* do a 'conventional' protected call */
    status = luaD_pcall(L, f_call, &c, savestack(L, c.func), func);
  }
  else {  /* prepare continuation (call is already protected by 'resume') */
    CallInfo *ci = L->ci;
    ci->u.c.k = k;  /* save continuation */
    ci->u.c.ctx = ctx;  /* save context */
    /* save information for error recovery */
    ci->extra = savestack(L, c.func);
    ci->u.c.old_errfunc = L->errfunc;
    L->errfunc = func;
    setoah(ci->callstatus, L->allowhook);  /* save value of 'allowhook' */
    ci->callstatus |= CIST_YPCALL;  /* function can do error recovery */
    luaD_call(L, c.func, nresults);  /* do the call */
    ci->callstatus &= ~CIST_YPCALL;
    L->errfunc = ci->u.c.old_errfunc;
    status = LUA_OK;  /* if it is here, there were no errors */
  }
  adjustresults(L, nresults);
  lua_unlock(L);
  return status;
}

/* KEY-FUNCTION 
** 加载一段字符串，生成闭包。
** 没有完全看懂(gc)，遇到再看。
*/
LUA_API int lua_load (lua_State *L, lua_Reader reader, void *data,
                      const char *chunkname, const char *mode) {
  ZIO z;
  int status;
  lua_lock(L);
  if (!chunkname) chunkname = "?";
  
  luaZ_init(L, &z, reader, data);    /* 初始化读结构体 */
  
  status = luaD_protectedparser(L, &z, chunkname, mode);    /* 调用parser进行处理，是不是觉得这个单词很面熟，对的,编译原理走起来。。。 */
  
  if (status == LUA_OK) {  /* no errors? */
    LClosure *f = clLvalue(L->top - 1);  /* get newly created function */
    if (f->nupvalues >= 1) {  /* does it have an upvalue? */
        
      /* get global table from registry */
      Table *reg = hvalue(&G(L)->l_registry);
      const TValue *gt = luaH_getint(reg, LUA_RIDX_GLOBALS);
    
      /* set global table as 1st upvalue of 'f' (may be LUA_ENV) */
      setobj(L, f->upvals[0]->v, gt);
      luaC_upvalbarrier(L, f->upvals[0]);
    }
  }
  lua_unlock(L);
  return status;
}

LUA_API int lua_dump (lua_State *L, lua_Writer writer, void *data, int strip) {
  int status;
  TValue *o;
  lua_lock(L);
  api_checknelems(L, 1);
  o = L->top - 1;
  if (isLfunction(o))
    status = luaU_dump(L, getproto(o), writer, data, strip);
  else
    status = 1;
  lua_unlock(L);
  return status;
}

/* 纯粹的API函数 */
LUA_API int lua_status (lua_State *L) {
  return L->status;
}

/*
** Garbage-collection function
*/

LUA_API int lua_gc (lua_State *L, int what, int data) {
  int res = 0;
  global_State *g;
  lua_lock(L);
  g = G(L);
  switch (what) {
    case LUA_GCSTOP: {
      g->gcrunning = 0;
      break;
    }
    case LUA_GCRESTART: {
      luaE_setdebt(g, 0);
      g->gcrunning = 1;
      break;
    }
    case LUA_GCCOLLECT: {
      luaC_fullgc(L, 0);
      break;
    }
    case LUA_GCCOUNT: {
      /* GC values are expressed in Kbytes: #bytes/2^10 */
      res = cast_int(gettotalbytes(g) >> 10);
      break;
    }
    case LUA_GCCOUNTB: {    /* 0x3ff:用bits画下 */
      res = cast_int(gettotalbytes(g) & 0x3ff);
      break;
    }
    case LUA_GCSTEP: {
      l_mem debt = 1;  /* =1 to signal that it did an actual step */
      lu_byte oldrunning = g->gcrunning;
      g->gcrunning = 1;  /* allow GC to run */
      if (data == 0) {
        luaE_setdebt(g, -GCSTEPSIZE);  /* to do a "small" step */
        luaC_step(L);
      }
      else {  /* add 'data' to total debt */
        debt = cast(l_mem, data) * 1024 + g->GCdebt;
        luaE_setdebt(g, debt);
        luaC_checkGC(L);
      }
      g->gcrunning = oldrunning;  /* restore previous state */
      if (debt > 0 && g->gcstate == GCSpause)  /* end of cycle? */
        res = 1;  /* signal it */
      break;
    }
    case LUA_GCSETPAUSE: {
      res = g->gcpause;
      g->gcpause = data;
      break;
    }
    case LUA_GCSETSTEPMUL: {
      res = g->gcstepmul;
      if (data < 40) data = 40;  /* avoid ridiculous low values (and 0) */
      g->gcstepmul = data;
      break;
    }
    case LUA_GCISRUNNING: {
      res = g->gcrunning;
      break;
    }
    default: res = -1;  /* invalid option */
  }
  lua_unlock(L);
  return res;
}

/*
** miscellaneous(杂) functions
*/

LUA_API int lua_error (lua_State *L) {
  lua_lock(L);
  api_checknelems(L, 1);
  luaG_errormsg(L);
  /* code unreachable; will unlock when control actually leaves the kernel */
  return 0;  /* to avoid warnings */
}

/* table == statck[idx], key==top-1的下一对key<-->value */
LUA_API int lua_next (lua_State *L, int idx) {
  StkId t;
  int more;
  lua_lock(L);
  
  t = index2addr(L, idx);    /* 找到表 */
  api_check(L, ttistable(t), "table expected");    /* 参数必须是个表 */
  
  more = luaH_next(L, hvalue(t), L->top - 1);
  if (more) {
    api_incr_top(L);    /* 找到了，且返回了key对应的value,所以这里堆栈要增长以便存下value */
  }
  else  /* no more elements */
    L->top -= 1;  /* remove key */
  
  lua_unlock(L);
  return more;
}

LUA_API void lua_concat (lua_State *L, int n) {
  lua_lock(L);
  api_checknelems(L, n);
  if (n >= 2) {
    luaC_checkGC(L);
    luaV_concat(L, n);
  }
  else if (n == 0) {  /* push empty string */
    setsvalue2s(L, L->top, luaS_newlstr(L, "", 0));
    api_incr_top(L);
  }
  /* else n == 1; nothing to do */
  lua_unlock(L);
}

/* 求"变量"的长度 */
LUA_API void lua_len (lua_State *L, int idx) {
  StkId t;
  lua_lock(L);
  t = index2addr(L, idx);
  luaV_objlen(L, L->top, t);
  api_incr_top(L);
  lua_unlock(L);
}

LUA_API lua_Alloc lua_getallocf (lua_State *L, void **ud) {
  lua_Alloc f;
  lua_lock(L);
  if (ud) *ud = G(L)->ud;
  f = G(L)->frealloc;
  lua_unlock(L);
  return f;
}

LUA_API void lua_setallocf (lua_State *L, lua_Alloc f, void *ud) {
  lua_lock(L);
  G(L)->ud = ud;
  G(L)->frealloc = f;
  lua_unlock(L);
}

//构建一个User'Data并压栈，返回UData中私有数据地址
LUA_API void *lua_newuserdata (lua_State *L, size_t size) {
  Udata *u;
  lua_lock(L);
  luaC_checkGC(L);
  
  /* 构建一份UserData数据 */
  u = luaS_newudata(L, size);
  
  /* 将上述构建的UserData压入栈顶 */
  setuvalue(L, L->top, u);
  api_incr_top(L);
  
  lua_unlock(L);
  return getudatamem(u);    /* 返回私有地址 */
}

/* 不太明白这个函数的作用 */
static const char *aux_upvalue (StkId fi, int n, TValue **val,
                                CClosure **owner, UpVal **uv) {
  switch (ttype(fi)) {
    case LUA_TCCL: {  /* C closure */
      CClosure *f = clCvalue(fi);
      if (!(1 <= n && n <= f->nupvalues)) return NULL;
      *val = &f->upvalue[n-1];
      if (owner) *owner = f;
      return "";
    }
    case LUA_TLCL: {  /* Lua closure */
      LClosure *f = clLvalue(fi);
      TString *name;
      Proto *p = f->p;
      if (!(1 <= n && n <= p->sizeupvalues)) return NULL;
      *val = f->upvals[n-1]->v;
      if (uv) *uv = f->upvals[n - 1];
      name = p->upvalues[n-1].name;
      return (name == NULL) ? "(*no name)" : getstr(name);
    }
    default: return NULL;  /* not a closure */
  }
}

/* 获取某个upvalue ? */
LUA_API const char *lua_getupvalue (lua_State *L, int funcindex, int n) {
  const char *name;
  TValue *val = NULL;  /* to avoid warnings */
  lua_lock(L);
  name = aux_upvalue(index2addr(L, funcindex), n, &val, NULL, NULL);
  if (name) {
    setobj2s(L, L->top, val);
    api_incr_top(L);
  }
  lua_unlock(L);
  return name;
}

/* 设置某个upvalue? */
LUA_API const char *lua_setupvalue (lua_State *L, int funcindex, int n) {
  const char *name;
  TValue *val = NULL;  /* to avoid warnings */
  CClosure *owner = NULL;
  UpVal *uv = NULL;
  StkId fi;
  lua_lock(L);
  fi = index2addr(L, funcindex);
  api_checknelems(L, 1);
  name = aux_upvalue(fi, n, &val, &owner, &uv);
  if (name) {
    L->top--;
    setobj(L, val, L->top);
    if (owner) { luaC_barrier(L, owner, L->top); }
    else if (uv) { luaC_upvalbarrier(L, uv); }
  }
  lua_unlock(L);
  return name;
}

static UpVal **getupvalref (lua_State *L, int fidx, int n, LClosure **pf) {
  LClosure *f;
  StkId fi = index2addr(L, fidx);
  api_check(L, ttisLclosure(fi), "Lua function expected");
  f = clLvalue(fi);
  api_check(L, (1 <= n && n <= f->p->sizeupvalues), "invalid upvalue index");
  if (pf) *pf = f;
  return &f->upvals[n - 1];  /* get its upvalue pointer */
}

LUA_API void *lua_upvalueid (lua_State *L, int fidx, int n) {
  StkId fi = index2addr(L, fidx);
  switch (ttype(fi)) {
    case LUA_TLCL: {  /* lua closure */
      return *getupvalref(L, fidx, n, NULL);
    }
    case LUA_TCCL: {  /* C closure */
      CClosure *f = clCvalue(fi);
      api_check(L, 1 <= n && n <= f->nupvalues, "invalid upvalue index");
      return &f->upvalue[n - 1];
    }
    default: {
      api_check(L, 0, "closure expected");
      return NULL;
    }
  }
}

LUA_API void lua_upvaluejoin (lua_State *L, int fidx1, int n1,
                                            int fidx2, int n2) {
  LClosure *f1;
  UpVal **up1 = getupvalref(L, fidx1, n1, &f1);
  UpVal **up2 = getupvalref(L, fidx2, n2, NULL);
  luaC_upvdeccount(L, *up1);
  *up1 = *up2;
  (*up1)->refcount++;
  if (upisopen(*up1)) (*up1)->u.open.touched = 1;
  luaC_upvalbarrier(L, *up1);
}