api: claim lua_isyieldable reads

Author: Frityet

notes/api-debug-claim-cleanup.md

@@ -53,6 +53,8 @@ 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_isyieldable()` now follows the same read-only claim shape as
+  `lua_status()`/`lua_gettop()` before reading `L->cframe`.
 - `lua_pushvfstring()` prechecks target ownership, drops the preclaim while
   formatting/interning through the current error state, then resume-claims the
   target for one-slot growth and string publication. `lua_pushfstring()`

notes/m5.md

@@ -2918,3 +2918,9 @@ M5 C wrapper callback publication:
   external C function entry.
 - Added `m5_wrapcf_func_publish` to reject raw C-side `->wrapf` access and pin
   the `wrapf_store()` before `BC_FUNCCW` publication order.
+
+M5 read-only C API owner claims:
+- `lua_isyieldable()` now claims the target state before reading `L->cframe`,
+  matching the already-claimed `lua_status()` and `lua_gettop()` public
+  read-only APIs. `m5_api_debug_claim_cleanup` now rejects regressions in that
+  claim/read/drop boundary.

src/lj_api.c

@@ -2198,7 +2198,13 @@ LUALIB_API int luaL_callmeta(lua_State *L, int idx, const char *field)
 
 LUA_API int lua_isyieldable(lua_State *L)
 {
-  return cframe_canyield(L->cframe);
+  LJStateClaim claim;
+  int ok;
+  if (!lj_state_tryclaim(L, lj_thr_current_id(G(L)), &claim))
+    lj_err_callermsg(api_errstate(L), "thread busy");
+  ok = cframe_canyield(L->cframe);
+  lj_state_dropclaim(&claim);
+  return ok;
 }
 
 LUA_API int lua_yield(lua_State *L, int nresults)

tests/suites/m5_publication.lua

@@ -515,6 +515,21 @@ END {
     exit 1
   }
 }
+]=], "src/lj_api.c")
+
+  awk([=[
+BEGIN { infn = 0; claim = 0; read = 0; drop = 0 }
+/^LUA_API int lua_isyieldable\(lua_State \*L\)/ { infn = 1; next }
+infn && /^}/ { infn = 0; next }
+infn && /lj_state_tryclaim/ { claim = NR }
+infn && /cframe_canyield\(L->cframe\)/ { read = NR }
+infn && /lj_state_dropclaim\(&claim\)/ { drop = NR }
+END {
+  if (!claim || !read || !drop || claim > read || read > drop) {
+    print "lua_isyieldable owner-claim boundary missing"
+    exit 1
+  }
+}
 ]=], "src/lj_api.c")
 
   awk([=[