New API function 'lua_closeslot'

Closing a to-be-closed variable with 'lua_settop' is too restrictive,
as it erases all slots above the variable. Moreover, it adds side
effects to 'lua_settop', which should be a fairly basic function.
This commit is contained in:
Roberto Ierusalimschy 2021-01-11 15:03:01 -03:00
parent ce101dcaf7
commit cc1692515e
6 changed files with 66 additions and 29 deletions

19
lapi.c
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@ -187,9 +187,26 @@ LUA_API void lua_settop (lua_State *L, int idx) {
api_check(L, -(idx+1) <= (L->top - (func + 1)), "invalid new top");
diff = idx + 1; /* will "subtract" index (as it is negative) */
}
#if defined(LUA_COMPAT_5_4_0)
if (diff < 0 && hastocloseCfunc(ci->nresults))
luaF_close(L, L->top + diff, CLOSEKTOP);
L->top += diff; /* correct top only after closing any upvalue */
#endif
L->top += diff;
api_check(L, L->openupval == NULL || uplevel(L->openupval) < L->top,
"cannot pop an unclosed slot");
lua_unlock(L);
}
LUA_API void lua_closeslot (lua_State *L, int idx) {
StkId level;
lua_lock(L);
level = index2stack(L, idx);
api_check(L, hastocloseCfunc(L->ci->nresults) && L->openupval != NULL &&
uplevel(L->openupval) == level,
"no variable to close at given level");
luaF_close(L, level, CLOSEKTOP);
setnilvalue(s2v(level));
lua_unlock(L);
}

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@ -545,10 +545,8 @@ static char *prepbuffsize (luaL_Buffer *B, size_t sz, int boxidx) {
if (buffonstack(B)) /* buffer already has a box? */
newbuff = (char *)resizebox(L, boxidx, newsize); /* resize it */
else { /* no box yet */
lua_pushnil(L); /* reserve slot for final result */
newbox(L); /* create a new box */
/* move box (and slot) to its intended position */
lua_rotate(L, boxidx - 1, 2);
lua_insert(L, boxidx); /* move box to its intended position */
lua_toclose(L, boxidx);
newbuff = (char *)resizebox(L, boxidx, newsize);
memcpy(newbuff, B->b, B->n * sizeof(char)); /* copy original content */
@ -585,8 +583,8 @@ LUALIB_API void luaL_pushresult (luaL_Buffer *B) {
lua_State *L = B->L;
lua_pushlstring(L, B->b, B->n);
if (buffonstack(B)) {
lua_copy(L, -1, -3); /* move string to reserved slot */
lua_pop(L, 2); /* pop string and box (closing the box) */
lua_closeslot(L, -2); /* close the box */
lua_remove(L, -2); /* remove box from the stack */
}
}

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@ -1766,6 +1766,9 @@ static struct X { int x; } x;
else if EQ("toclose") {
lua_toclose(L1, getnum);
}
else if EQ("closeslot") {
lua_closeslot(L1, getnum);
}
else luaL_error(L, "unknown instruction %s", buff);
}
return 0;

3
lua.h
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@ -347,7 +347,8 @@ LUA_API size_t (lua_stringtonumber) (lua_State *L, const char *s);
LUA_API lua_Alloc (lua_getallocf) (lua_State *L, void **ud);
LUA_API void (lua_setallocf) (lua_State *L, lua_Alloc f, void *ud);
LUA_API void (lua_toclose) (lua_State *L, int idx);
LUA_API void (lua_toclose) (lua_State *L, int idx);
LUA_API void (lua_closeslot) (lua_State *L, int idx);
/*

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@ -3095,6 +3095,18 @@ will probably need to close states as soon as they are not needed.
}
@APIEntry{void lua_closeslot (lua_State *L, int index);|
@apii{0,0,e}
Close the to-be-closed slot at the given index and set its value to @nil.
The index must be the last index previously marked to be closed
@see{lua_toclose} that is still active (that is, not closed yet).
(Exceptionally, this function was introduced in release 5.4.3.
It is not present in previous 5.4 releases.)
}
@APIEntry{int lua_compare (lua_State *L, int index1, int index2, int op);|
@apii{0,0,e}
@ -3747,9 +3759,7 @@ except that it allows the called function to yield @see{continuations}.
@apii{n,0,e}
Pops @id{n} elements from the stack.
This function can run arbitrary code when removing an index
marked as to-be-closed from the stack.
It is implemented as a macro over @Lid{lua_settop}.
}
@ -4240,8 +4250,12 @@ If the new top is greater than the old one,
then the new elements are filled with @nil.
If @id{index} @N{is 0}, then all stack elements are removed.
This function can run arbitrary code when removing an index
marked as to-be-closed from the stack.
For compatibility reasons,
this function may close slots marked as to-be-closed @see{lua_toclose},
and therefore it can run arbitrary code.
You should not rely on this behavior:
Instead, always close to-be-closed slots explicitly,
with @Lid{lua_closeslot}, before removing them from the stack.
}
@ -4337,10 +4351,9 @@ when it goes out of scope.
Here, in the context of a C function,
to go out of scope means that the running function returns to Lua,
there is an error,
or the index is removed from the stack through
@Lid{lua_settop} or @Lid{lua_pop}.
An index marked as to-be-closed should not be removed from the stack
by any other function in the API except @Lid{lua_settop} or @Lid{lua_pop}.
or there is a call to @Lid{lua_closeslot}.
An index marked as to-be-closed should neither be removed from the stack
nor modified before a corresponding call to @Lid{lua_closeslot}.
This function should not be called for an index
that is equal to or below an active to-be-closed index.
@ -4353,7 +4366,7 @@ Note that, both in case of errors and of a regular return,
by the time the @idx{__close} metamethod runs,
the @N{C stack} was already unwound,
so that any automatic @N{C variable} declared in the calling function
will be out of scope.
(e.g., a buffer) will be out of scope.
}

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@ -507,10 +507,12 @@ function checkerrnopro (code, msg)
end
if not _soft then
collectgarbage("stop") -- avoid __gc with full stack
checkerrnopro("pushnum 3; call 0 0", "attempt to call")
print"testing stack overflow in unprotected thread"
function f () f() end
checkerrnopro("getglobal 'f'; call 0 0;", "stack overflow")
collectgarbage("restart")
end
print"+"
@ -1125,26 +1127,29 @@ do
assert(#openresource == n)
end
-- closing resources with 'settop'
-- closing resources with 'closeslot'
_ENV.xxx = true
local a = T.testC([[
pushvalue 2
call 0 1 # create resource
pushvalue 2 # stack: S, NR, CH
call 0 1 # create resource; stack: S, NR, CH, R
toclose -1 # mark it to be closed
pushvalue 2
call 0 1 # create another resource
pushvalue 2 # stack: S, NR, CH, R, NR
call 0 1 # create another resource; stack: S, NR, CH, R, R
toclose -1 # mark it to be closed
pushvalue 3
pushvalue 3 # stack: S, NR, CH, R, R, CH
pushint 2 # there should be two open resources
call 1 0
pop 1 # pop second resource from the stack
pushvalue 3
call 1 0 # stack: S, NR, CH, R, R
closeslot -1 # close second resource
pushvalue 3 # stack: S, NR, CH, R, R, CH
pushint 1 # there should be one open resource
call 1 0
pop 1 # pop second resource from the stack
call 1 0 # stack: S, NR, CH, R, R
closeslot 4
setglobal "xxx" # previous op. erased the slot
pop 1 # pop other resource from the stack
pushint *
return 1 # return stack size
]], newresource, check)
assert(a == 3) -- no extra items left in the stack
assert(a == 3 and _ENV.xxx == nil) -- no extra items left in the stack
-- non-closable value
local a, b = pcall(T.makeCfunc[[