api: claim ownerless C closure pushes

Author: Frityet

notes/api-debug-claim-cleanup.md

@@ -44,6 +44,12 @@ Permanent shape:
   allocation, then resume-claim to publish the stack slot. `lua_newuserdata()`
   and `lua_newthread()` snapshot the target current environment before dropping
   the preclaim.
+- `lua_pushcclosure()` prechecks the target stack and snapshots the current
+  environment under a target-state claim, drops that preclaim for closure
+  allocation, then resume-claims to revalidate the stack, copy upvalues, and
+  publish the closure result. Zero-upvalue closures use protected one-slot
+  growth; closures with upvalues replace existing stack slots without requiring
+  extra stack capacity.
 - Public read-only stack getter/conversion APIs (`lua_type`,
   `lua_iscfunction`, `lua_isnumber`, `lua_isstring`, `lua_isuserdata`,
   `lua_rawequal`, `lua_tonumber`, `lua_tonumberx`, `lua_tointeger`,

src/lj_api.c

@@ -1190,19 +1190,33 @@ LUA_API const char *lua_pushfstring(lua_State *L, const char *fmt, ...)
 
 LUA_API void lua_pushcclosure(lua_State *L, lua_CFunction f, int n)
 {
+  LJStateClaim preclaim, claim;
+  lua_State *errL;
+  GCtab *env;
   GCfunc *fn;
-  lj_gc_check(L);
+  int nup = n;
+  api_checkclaim(L, &preclaim);
   lj_checkapi_slot(n);
-  fn = lj_func_newC(L, (MSize)n, getcurrenv(L));
+  env = getcurrenv(L);
+  lj_state_dropclaim(&preclaim);
+  errL = api_errstate(L);
+  fn = lj_func_newC(errL, (MSize)n, env);
   fn->c.f = f;
-  L->top -= n;
-  while (n--) {
-    copyTVrel(L, &fn->c.upvalue[n], L->top+n);
-    lj_gc_pubobjtv(L, fn, &fn->c.upvalue[n]);
+  if (!lj_state_resumeclaim(L, lj_thr_current_id(G(L)), &claim))
+    lj_err_callermsg(errL, "thread busy");
+  lj_checkapi_slot(nup);
+  if (nup == 0)
+    api_checkstack1_claimed(L, errL, &claim);
+  L->top -= nup;
+  while (nup--) {
+    copyTVrel(L, &fn->c.upvalue[nup], L->top+nup);
+    lj_gc_pubobjtv(L, fn, &fn->c.upvalue[nup]);
   }
   setfuncV(L, L->top, fn);
+  lj_state_stack_pubtv(L, L, L->top);
   lj_assertL(iswhite(obj2gco(fn)), "new GC object is not white");
-  incr_top(L);
+  L->top++;
+  lj_state_dropresumeclaim(&claim);
 }
 
 LUA_API void lua_pushboolean(lua_State *L, int b)

tests/suites/m5_publication.lua

@@ -218,6 +218,52 @@ function count_char(text, ch,    n, i) {
     if (substr(text, i, 1) == ch) n++
   return n
 }
+BEGIN {
+  infn = 0; started = 0; depth = 0
+  pre = 0; slot1 = 0; env = 0; pre_drop = 0; alloc = 0; claim = 0
+  slot2 = 0; zerogrow = 0; grow = 0; copy = 0; store = 0
+  publish = 0; drop = 0
+}
+/^LUA_API void lua_pushcclosure\(lua_State \*L,/ { infn = 1; next }
+infn {
+  if (index($0, "{")) started = 1
+  depth += count_char($0, "{")
+  depth -= count_char($0, "}")
+  if (/api_checkclaim\(L, &preclaim\)/) pre = NR
+  if (/lj_checkapi_slot\(n\)/) slot1 = NR
+  if (/getcurrenv/) env = NR
+  if (/lj_state_dropclaim\(&preclaim\)/) pre_drop = NR
+  if (/lj_func_newC/) alloc = NR
+  if (/lj_state_resumeclaim/) claim = NR
+  if (/lj_checkapi_slot\(nup\)/) slot2 = NR
+  if (/nup == 0/) zerogrow = NR
+  if (/api_checkstack1_claimed/) grow = NR
+  if (/copyTVrel\(L, &fn->c.upvalue/) copy = NR
+  if (/setfuncV/) store = NR
+  if (/lj_state_stack_pubtv/) publish = NR
+  if (/lj_state_dropresumeclaim/) drop = NR
+  if (started && depth == 0) infn = 0
+}
+END {
+  if (!pre || !slot1 || !env || !pre_drop || !alloc || !claim || !slot2 ||
+      !zerogrow || !grow || !copy || !store || !publish || !drop ||
+      pre > slot1 || slot1 > env || env > pre_drop || pre_drop > alloc ||
+      alloc > claim || claim > slot2 || slot2 > zerogrow ||
+      zerogrow > grow || grow > copy || copy > store || store > publish ||
+      publish > drop) {
+    print "lua_pushcclosure must snapshot env, allocate unclaimed, and publish claimed"
+    exit 1
+  }
+}
+]=], "src/lj_api.c")
+
+  awk([=[
+function count_char(text, ch,    n, i) {
+  n = 0
+  for (i = 1; i <= length(text); i++)
+    if (substr(text, i, 1) == ch) n++
+  return n
+}
 BEGIN {
   infn = 0; started = 0; depth = 0
   pre = 0; env = 0; pre_drop = 0; alloc = 0; claim = 0; grow = 0

tests/t-state-owner.c

@@ -131,6 +131,15 @@ static void check_stack_api_unowned(lua_State *L)
   assert(lua_gettop(co) == 14 && lua_isuserdata(co, 14));
   assert(lua_newthread(co) == lua_tothread(co, 15));
   assert(lua_gettop(co) == 15 && lua_type(co, 15) == LUA_TTHREAD);
+  lua_pushcclosure(co, resume_return, 0);
+  assert(lua_gettop(co) == 16 && lua_iscfunction(co, 16));
+  lua_call(co, 0, 1);
+  assert(lua_gettop(co) == 16 && lua_tointeger(co, 16) == 91);
+  lua_pushinteger(co, 70);
+  lua_pushcclosure(co, c_upvalue_return, 1);
+  assert(lua_gettop(co) == 17 && lua_iscfunction(co, 17));
+  lua_call(co, 0, 1);
+  assert(lua_gettop(co) == 17 && lua_tointeger(co, 17) == 70);
   lua_settop(co, 3);
   lua_settop(co, 5);
   assert(lua_gettop(co) == 5);
@@ -740,6 +749,14 @@ static int busy_lua_newthread_api(lua_State *L)
   return 0;
 }
 
+static int busy_lua_pushcclosure_api(lua_State *L)
+{
+  lua_State *co = lua_newthread(L);
+  busy_stack_prepare(L, co);
+  lua_pushcclosure(co, c_upvalue_return, 1);
+  return 0;
+}
+
 static lua_State *busy_getter_prepare(lua_State *L)
 {
   lua_State *co = lua_newthread(L);
@@ -1377,6 +1394,7 @@ int main(void)
   expect_thread_busy(L, busy_lua_createtable, "busy lua_createtable");
   expect_thread_busy(L, busy_lua_newuserdata, "busy lua_newuserdata");
   expect_thread_busy(L, busy_lua_newthread_api, "busy lua_newthread");
+  expect_thread_busy(L, busy_lua_pushcclosure_api, "busy lua_pushcclosure");
   expect_thread_busy(L, busy_lua_type, "busy lua_type");
   expect_thread_busy(L, busy_lua_isnumber, "busy lua_isnumber");
   expect_thread_busy(L, busy_lua_isstring, "busy lua_isstring");