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Avoid shrinking stacks to often

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Shrink a stack only when the final stack size can be at most 2/3 the
previous size with half of its entries empty. This commit also
improves the clarity of 'luaD_growstack'.
This commit is contained in:
Roberto Ierusalimschy
2020-10-06 13:37:41 -03:00
parent fb172d0a92
commit 9ecd446141
2 changed files with 87 additions and 17 deletions
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54
ldo.c
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@@ -207,50 +207,72 @@ int luaD_reallocstack (lua_State *L, int newsize, int raiseerror) {
*/
int luaD_growstack (lua_State *L, int n, int raiseerror) {
int size = L->stacksize;
int newsize = 2 * size; /* tentative new size */
if (unlikely(size > LUAI_MAXSTACK)) { /* need more space after extra size? */
if (unlikely(size > LUAI_MAXSTACK)) {
/* if stack is larger than maximum, thread is already using the
extra space reserved for errors, that is, thread is handling
a stack error; cannot grow further than that. */
lua_assert(L->stacksize == ERRORSTACKSIZE);
if (raiseerror)
luaD_throw(L, LUA_ERRERR); /* error inside message handler */
else return 0;
return 0; /* if not 'raiseerror', just signal it */
}
else {
int newsize = 2 * size; /* tentative new size */
int needed = cast_int(L->top - L->stack) + n + EXTRA_STACK;
if (newsize > LUAI_MAXSTACK) /* cannot cross the limit */
newsize = LUAI_MAXSTACK;
if (newsize < needed) /* but must respect what was asked for */
newsize = needed;
if (unlikely(newsize > LUAI_MAXSTACK)) { /* stack overflow? */
if (likely(newsize <= LUAI_MAXSTACK))
return luaD_reallocstack(L, newsize, raiseerror);
else { /* stack overflow */
/* add extra size to be able to handle the error message */
luaD_reallocstack(L, ERRORSTACKSIZE, raiseerror);
if (raiseerror)
luaG_runerror(L, "stack overflow");
else return 0;
return 0;
}
} /* else no errors */
return luaD_reallocstack(L, newsize, raiseerror);
}
}
static int stackinuse (lua_State *L) {
CallInfo *ci;
int res;
StkId lim = L->top;
for (ci = L->ci; ci != NULL; ci = ci->previous) {
if (lim < ci->top) lim = ci->top;
}
lua_assert(lim <= L->stack_last);
return cast_int(lim - L->stack) + 1; /* part of stack in use */
res = cast_int(lim - L->stack) + 1; /* part of stack in use */
if (res < LUA_MINSTACK)
res = LUA_MINSTACK; /* ensure a minimum size */
return res;
}
/*
** If stack size is more than 3 times the current use, reduce that size
** to twice the current use. (So, the final stack size is at most 2/3 the
** previous size, and half of its entries are empty.)
** As a particular case, if stack was handling a stack overflow and now
** it is not, 'max' (limited by LUAI_MAXSTACK) will be smaller than
** 'stacksize' (equal to ERRORSTACKSIZE in this case), and so the stack
** will be reduced to a "regular" size.
*/
void luaD_shrinkstack (lua_State *L) {
int inuse = stackinuse(L);
int goodsize = inuse + BASIC_STACK_SIZE;
if (goodsize > LUAI_MAXSTACK)
goodsize = LUAI_MAXSTACK; /* respect stack limit */
int nsize = inuse * 2; /* proposed new size */
int max = inuse * 3; /* maximum "reasonable" size */
if (max > LUAI_MAXSTACK) {
max = LUAI_MAXSTACK; /* respect stack limit */
if (nsize > LUAI_MAXSTACK)
nsize = LUAI_MAXSTACK;
}
/* if thread is currently not handling a stack overflow and its
good size is smaller than current size, shrink its stack */
if (inuse <= (LUAI_MAXSTACK - EXTRA_STACK) && goodsize < L->stacksize)
luaD_reallocstack(L, goodsize, 0); /* ok if that fails */
size is larger than maximum "reasonable" size, shrink it */
if (inuse <= (LUAI_MAXSTACK - EXTRA_STACK) && L->stacksize > max)
luaD_reallocstack(L, nsize, 0); /* ok if that fails */
else /* don't change stack */
condmovestack(L,{},{}); /* (change only for debugging) */
luaE_shrinkCI(L); /* shrink CI list */
@@ -625,7 +647,7 @@ static int recover (lua_State *L, int status) {
luaD_seterrorobj(L, status, oldtop);
L->ci = ci;
L->allowhook = getoah(ci->callstatus); /* restore original 'allowhook' */
luaD_shrinkstack(L);
luaD_shrinkstack(L); /* restore stack size in case of overflow */
L->errfunc = ci->u.c.old_errfunc;
return 1; /* continue running the coroutine */
}
@@ -768,7 +790,7 @@ int luaD_pcall (lua_State *L, Pfunc func, void *u,
status = luaF_close(L, oldtop, status);
oldtop = restorestack(L, old_top); /* previous call may change stack */
luaD_seterrorobj(L, status, oldtop);
luaD_shrinkstack(L);
luaD_shrinkstack(L); /* restore stack size in case of overflow */
}
L->errfunc = old_errfunc;
return status;