/*
** $Id: lgc.h,v 2.14 2005/06/07 18:53:45 roberto Exp roberto $
** Garbage Collector
** See Copyright Notice in lua.h
*/

#ifndef lgc_h
#define lgc_h


#include "lobject.h"


/*
** Possible states of the Garbage Collector
*/
#define GCSpause	0
#define GCSpropagate	1
#define GCSsweepstring	2
#define GCSsweep	3
#define GCSfinalize	4


/*
** some userful bit tricks
*/
#define resetbits(x,m)	((x) &= cast(lu_byte, ~(m)))
#define setbits(x,m)	((x) |= (m))
#define testbits(x,m)	((x) & (m))
#define bitmask(b)	(1<<(b))
#define bit2mask(b1,b2)	(bitmask(b1) | bitmask(b2)) // 按位或，是组合bit map的操作
#define l_setbit(x,b)	setbits(x, bitmask(b)) // bit map组合赋值
#define resetbit(x,b)	resetbits(x, bitmask(b))
#define testbit(x,b)	testbits(x, bitmask(b))
#define set2bits(x,b1,b2)	setbits(x, (bit2mask(b1, b2)))
#define reset2bits(x,b1,b2)	resetbits(x, (bit2mask(b1, b2)))
#define test2bits(x,b1,b2)	testbits(x, (bit2mask(b1, b2)))



/*
** Layout for bit use in `marked' field:
** bit 0 - object is white (type 0)
** bit 1 - object is white (type 1)
** bit 2 - object is black
** bit 3 - for userdata: has been finalized
** bit 3 - for tables: has weak keys
** bit 4 - for tables: has weak values
** bit 5 - object is fixed (should not be collected)
** bit 6 - object is "super" fixed (only the main thread)
*/


#define WHITE0BIT	0
#define WHITE1BIT	1
#define BLACKBIT	2
#define FINALIZEDBIT	3
#define KEYWEAKBIT	3
#define VALUEWEAKBIT	4
#define FIXEDBIT	5
#define SFIXEDBIT	6
#define WHITEBITS	bit2mask(WHITE0BIT, WHITE1BIT) // 0000 0011


#define iswhite(x)      test2bits((x)->gch.marked, WHITE0BIT, WHITE1BIT)
#define isblack(x)      testbit((x)->gch.marked, BLACKBIT)
#define isgray(x)	(!isblack(x) && !iswhite(x))

#define otherwhite(g)	(g->currentwhite ^ WHITEBITS) // 按位异或，最终仅otherwhite的bit位、FIXEDBIT对应的bit位上为1，例值：0010 0001、0010 0010
#define isdead(g,v)	((v)->gch.marked & otherwhite(g) & WHITEBITS) // v的marked标记中带有otherwhite，说明它是已经死掉的obj

#define changewhite(x)	((x)->gch.marked ^= WHITEBITS)
#define gray2black(x)	l_setbit((x)->gch.marked, BLACKBIT)

#define valiswhite(x)	(iscollectable(x) && iswhite(gcvalue(x)))

// currentwhite是个bit map，初始时它的数值会附带上FIXEDBIT，所以这里要做一下筛去操作，仅保留白色的bit信息
#define luaC_white(g)	cast(lu_byte, (g)->currentwhite & WHITEBITS)

// condhardstacktests()是个调试宏，让括号内的语句视编译情况而执行，一般它会空执行，括号内容为：检查thread中的虚拟栈槽位是否足够，并调整
// lua vm当前使用的总字节数 >= GCthreshold, 则触发一次luaC_step()
#define luaC_checkGC(L) { \
  condhardstacktests(luaD_reallocstack(L, L->stacksize - EXTRA_STACK - 1)); \
  if (G(L)->totalbytes >= G(L)->GCthreshold) \
	luaC_step(L); }

// v为TValue，向前设置屏障
// p是黑色 且 v是白色，尝试处理v
#define luaC_barrier(L,p,v) { if (valiswhite(v) && isblack(obj2gco(p)))  \
	luaC_barrierf(L,obj2gco(p),gcvalue(v)); }

// 向后设置屏障
// t是黑色 且 v是白色，处理t，t复灰
#define luaC_barriert(L,t,v) { if (valiswhite(v) && isblack(obj2gco(t)))  \
	luaC_barrierback(L,t); }

// o为gcObj，向前设置屏障
#define luaC_objbarrier(L,p,o)  \
	{ if (iswhite(obj2gco(o)) && isblack(obj2gco(p))) \
		luaC_barrierf(L,obj2gco(p),obj2gco(o)); }

// 向后设置屏障
#define luaC_objbarriert(L,t,o)  \
   { if (iswhite(obj2gco(o)) && isblack(obj2gco(t))) luaC_barrierback(L,t); }

LUAI_FUNC size_t luaC_separateudata (lua_State *L, int all);
LUAI_FUNC void luaC_callGCTM (lua_State *L);
LUAI_FUNC void luaC_freeall (lua_State *L);
LUAI_FUNC void luaC_step (lua_State *L);
LUAI_FUNC void luaC_fullgc (lua_State *L);
LUAI_FUNC void luaC_link (lua_State *L, GCObject *o, lu_byte tt);
LUAI_FUNC void luaC_linkupval (lua_State *L, UpVal *uv);
LUAI_FUNC void luaC_barrierf (lua_State *L, GCObject *o, GCObject *v);
LUAI_FUNC void luaC_barrierback (lua_State *L, Table *t);


#endif