GC checks stack space before running finalizerHEADmaster

If the stack does not have some minimum available space, the GC defers
calling a finalizer until the next cycle. That avoids errors while
running a finalizer that the programmer cannot control.

1 files changed, 11 insertions, 0 deletions

diff --git a/ldo.c b/ldo.c
index 75ce1488..6d0184ec 100644
--- a/ldo.c
+++ b/ldo.c
@@ -221,6 +221,17 @@ l_noret luaD_errerr (lua_State *L) {
 
 
 /*
+** Check whether stack has enough space to run a simple function (such
+** as a finalizer): At least BASIC_STACK_SIZE in the Lua stack and
+** 2 slots in the C stack.
+*/
+int luaD_checkminstack (lua_State *L) {
+  return ((stacksize(L) < MAXSTACK - BASIC_STACK_SIZE) &&
+          (getCcalls(L) < LUAI_MAXCCALLS - 2));
+}
+
+
+/*
 ** In ISO C, any pointer use after the pointer has been deallocated is
 ** undefined behavior. So, before a stack reallocation, all pointers
 ** should be changed to offsets, and after the reallocation they should