From 287b302acb8d925178e9edb800f0a8d18c7d35f6 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 23 Sep 2020 10:18:01 -0300
Subject: Revision of stackless implementation

- more organized handling of 'nCcalls'
- comments
- deprecation of 'setcstacklimit'
---
 lstate.h | 56 ++++++++++----------------------------------------------
 1 file changed, 10 insertions(+), 46 deletions(-)

(limited to 'lstate.h')

diff --git a/lstate.h b/lstate.h
index 983aa0d5..a05db376 100644
--- a/lstate.h
+++ b/lstate.h
@@ -87,48 +87,12 @@
 
 
 /*
-** About 'nCcalls': each thread in Lua (a lua_State) keeps a count of
-** how many "C calls" it still can do in the C stack, to avoid C-stack
-** overflow.  This count is very rough approximation; it considers only
-** recursive functions inside the interpreter, as non-recursive calls
-** can be considered using a fixed (although unknown) amount of stack
-** space.
-**
-** The count has two parts: the lower part is the count itself; the
-** higher part counts the number of non-yieldable calls in the stack.
-** (They are together so that we can change both with one instruction.)
-**
-** Because calls to external C functions can use an unknown amount
-** of space (e.g., functions using an auxiliary buffer), calls
-** to these functions add more than one to the count (see CSTACKCF).
-**
-** The proper count excludes the number of CallInfo structures allocated
-** by Lua, as a kind of "potential" calls. So, when Lua calls a function
-** (and "consumes" one CallInfo), it needs neither to decrement nor to
-** check 'nCcalls', as its use of C stack is already accounted for.
-*/
-
-/* number of "C stack slots" used by an external C function */
-#define CSTACKCF	10
-
-
-/*
-** The C-stack size is sliced in the following zones:
-** - larger than CSTACKERR: normal stack;
-** - [CSTACKMARK, CSTACKERR]: buffer zone to signal a stack overflow;
-** - [CSTACKCF, CSTACKERRMARK]: error-handling zone;
-** - below CSTACKERRMARK: buffer zone to signal overflow during overflow;
-** (Because the counter can be decremented CSTACKCF at once, we need
-** the so called "buffer zones", with at least that size, to properly
-** detect a change from one zone to the next.)
+** About 'nCcalls':  This count has two parts: the lower 16 bits counts
+** the number of recursive invocations in the C stack; the higher
+** 16 bits counts the number of non-yieldable calls in the stack.
+** (They are together so that we can change and save both with one
+** instruction.)
 */
-#define CSTACKERR	(8 * CSTACKCF)
-#define CSTACKMARK	(CSTACKERR - (CSTACKCF + 2))
-#define CSTACKERRMARK	(CSTACKCF + 2)
-
-
-/* initial limit for the C-stack of threads */
-#define CSTACKTHREAD	(2 * CSTACKERR)
 
 
 /* true if this thread does not have non-yieldable calls in the stack */
@@ -144,7 +108,8 @@
 /* Decrement the number of non-yieldable calls */
 #define decnny(L)	((L)->nCcalls -= 0x10000)
 
-
+/* Non-yieldable call increment */
+#define nyci	(0x10000 | 1)
 
 
 
@@ -290,7 +255,6 @@ typedef struct global_State {
   TString *strcache[STRCACHE_N][STRCACHE_M];  /* cache for strings in API */
   lua_WarnFunction warnf;  /* warning function */
   void *ud_warn;         /* auxiliary data to 'warnf' */
-  unsigned int Cstacklimit;  /* current limit for the C stack */
 } global_State;
 
 
@@ -314,7 +278,7 @@ struct lua_State {
   CallInfo base_ci;  /* CallInfo for first level (C calling Lua) */
   volatile lua_Hook hook;
   ptrdiff_t errfunc;  /* current error handling function (stack index) */
-  l_uint32 nCcalls;  /* number of allowed nested C calls - 'nci' */
+  l_uint32 nCcalls;  /* number of nested (non-yieldable | C)  calls */
   int oldpc;  /* last pc traced */
   int stacksize;
   int basehookcount;
@@ -383,11 +347,11 @@ LUAI_FUNC void luaE_freethread (lua_State *L, lua_State *L1);
 LUAI_FUNC CallInfo *luaE_extendCI (lua_State *L);
 LUAI_FUNC void luaE_freeCI (lua_State *L);
 LUAI_FUNC void luaE_shrinkCI (lua_State *L);
+LUAI_FUNC void luaE_checkcstack (lua_State *L);
+LUAI_FUNC void luaE_incCstack (lua_State *L);
 LUAI_FUNC void luaE_warning (lua_State *L, const char *msg, int tocont);
 LUAI_FUNC void luaE_warnerror (lua_State *L, const char *where);
 
 
-#define luaE_exitCcall(L)	((L)->nCcalls++)
-
 #endif
 
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