Why set useless stack slice(above L->top) to nil during gc atomic phase ?
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- Subject: Why set useless stack slice(above L->top) to nil during gc atomic phase ?
- From: 张伟智 <robotkzhang@...>
- Date: 2016年5月10日 18:07:40 +0800
Lua 5.2.4
In lgc.c propagatemark -> traversestack, line 502-506,
clear the slice in the range of [th->top + 1, th->stack + th->stacksize),
What if don't clear not-marked stack slice ?
495 static lu_mem traversestack (global_State *g, lua_State *th) {
496 int n = 0;
497 StkId o = th->stack;
498 if (o == NULL)
499 return 1; /* stack not completely built yet */
500 for (; o < th->top; o++) /* mark live elements in the stack */
501 markvalue(g, o);
502 if (g->gcstate == GCSatomic) { /* final traversal? */
503 StkId lim = th->stack + th->stacksize; /* real end of stack */
504 for (; o < lim; o++) /* clear not-marked stack slice */
505 setnilvalue(o);
506 }
507 else { /* count call infos to compute size */
508 CallInfo *ci;
509 for (ci = &th->base_ci; ci != th->ci; ci = ci->next)
510 n++;
511 }
512 return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
513 sizeof(CallInfo) * n;
514 }
Thanks.