Main thread is a regular field of global_State

They were already allocated as a single block, so there is no need
for the global_State to point to its main thread.

lapi.c

@@ -655,7 +655,7 @@ LUA_API int lua_pushthread (lua_State *L) {
   setthvalue(L, s2v(L->top.p), L);
   api_incr_top(L);
   lua_unlock(L);
-  return (G(L)->mainthread == L);
+  return (mainthread(G(L)) == L);
 }
 
 

ldo.c

@@ -132,11 +132,12 @@ l_noret luaD_throw (lua_State *L, TStatus errcode) {
   }
   else {  /* thread has no error handler */
     global_State *g = G(L);
+    lua_State *mainth = mainthread(g);
     errcode = luaE_resetthread(L, errcode);  /* close all upvalues */
     L->status = errcode;
-    if (g->mainthread->errorJmp) {  /* main thread has a handler? */
-      setobjs2s(L, g->mainthread->top.p++, L->top.p - 1);  /* copy error obj. */
-      luaD_throw(g->mainthread, errcode);  /* re-throw in main thread */
+    if (mainth->errorJmp) {  /* main thread has a handler? */
+      setobjs2s(L, mainth->top.p++, L->top.p - 1);  /* copy error obj. */
+      luaD_throw(mainth, errcode);  /* re-throw in main thread */
     }
     else {  /* no handler at all; abort */
       if (g->panic) {  /* panic function? */
@@ -961,7 +962,7 @@ LUA_API int lua_yieldk (lua_State *L, int nresults, lua_KContext ctx,
   ci = L->ci;
   api_checkpop(L, nresults);
   if (l_unlikely(!yieldable(L))) {
-    if (L != G(L)->mainthread)
+    if (L != mainthread(G(L)))
       luaG_runerror(L, "attempt to yield across a C-call boundary");
     else
       luaG_runerror(L, "attempt to yield from outside a coroutine");

lgc.c

@@ -78,7 +78,7 @@
 	((*getArrTag(t,i) & BIT_ISCOLLECTABLE) ? getArrVal(t,i)->gc : NULL)
 
 
-#define markvalue(g,o) { checkliveness(g->mainthread,o); \
+#define markvalue(g,o) { checkliveness(mainthread(g),o); \
   if (valiswhite(o)) reallymarkobject(g,gcvalue(o)); }
 
 #define markkey(g, n)	{ if keyiswhite(n) reallymarkobject(g,gckey(n)); }
@@ -441,7 +441,7 @@ static void cleargraylists (global_State *g) {
 static void restartcollection (global_State *g) {
   cleargraylists(g);
   g->GCmarked = 0;
-  markobject(g, g->mainthread);
+  markobject(g, mainthread(g));
   markvalue(g, &g->l_registry);
   markmt(g);
   markbeingfnz(g);  /* mark any finalizing object left from previous cycle */
@@ -1513,7 +1513,7 @@ void luaC_freeallobjects (lua_State *L) {
   separatetobefnz(g, 1);  /* separate all objects with finalizers */
   lua_assert(g->finobj == NULL);
   callallpendingfinalizers(L);
-  deletelist(L, g->allgc, obj2gco(g->mainthread));
+  deletelist(L, g->allgc, obj2gco(mainthread(g)));
   lua_assert(g->finobj == NULL);  /* no new finalizers */
   deletelist(L, g->fixedgc, NULL);  /* collect fixed objects */
   lua_assert(g->strt.nuse == 0);
@@ -1526,7 +1526,7 @@ static void atomic (lua_State *L) {
   GCObject *grayagain = g->grayagain;  /* save original list */
   g->grayagain = NULL;
   lua_assert(g->ephemeron == NULL && g->weak == NULL);
-  lua_assert(!iswhite(g->mainthread));
+  lua_assert(!iswhite(mainthread(g)));
   g->gcstate = GCSatomic;
   markobject(g, L);  /* mark running thread */
   /* registry and global metatables may be changed by API */

lstate.c

@@ -29,25 +29,6 @@
 
 
 
-/*
-** thread state + extra space
-*/
-typedef struct LX {
-  lu_byte extra_[LUA_EXTRASPACE];
-  lua_State l;
-} LX;
-
-
-/*
-** Main thread combines a thread state and the global state
-*/
-typedef struct LG {
-  LX l;
-  global_State g;
-} LG;
-
-
-
 #define fromstate(L)	(cast(LX *, cast(lu_byte *, (L)) - offsetof(LX, l)))
 
 
@@ -278,8 +259,8 @@ static void close_state (lua_State *L) {
   }
   luaM_freearray(L, G(L)->strt.hash, cast_sizet(G(L)->strt.size));
   freestack(L);
-  lua_assert(gettotalbytes(g) == sizeof(LG));
-  (*g->frealloc)(g->ud, fromstate(L), sizeof(LG), 0);  /* free main block */
+  lua_assert(gettotalbytes(g) == sizeof(global_State));
+  (*g->frealloc)(g->ud, g, sizeof(global_State), 0);  /* free main block */
 }
 
 
@@ -301,7 +282,7 @@ LUA_API lua_State *lua_newthread (lua_State *L) {
   L1->hook = L->hook;
   resethookcount(L1);
   /* initialize L1 extra space */
-  memcpy(lua_getextraspace(L1), lua_getextraspace(g->mainthread),
+  memcpy(lua_getextraspace(L1), lua_getextraspace(mainthread(g)),
          LUA_EXTRASPACE);
   luai_userstatethread(L, L1);
   stack_init(L1, L);  /* init stack */
@@ -352,11 +333,10 @@ LUA_API int lua_closethread (lua_State *L, lua_State *from) {
 LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud, unsigned seed) {
   int i;
   lua_State *L;
-  global_State *g;
-  LG *l = cast(LG *, (*f)(ud, NULL, LUA_TTHREAD, sizeof(LG)));
-  if (l == NULL) return NULL;
-  L = &l->l.l;
-  g = &l->g;
+  global_State *g = cast(global_State*,
+                       (*f)(ud, NULL, LUA_TTHREAD, sizeof(global_State)));
+  if (g == NULL) return NULL;
+  L = &g->mainth.l;
   L->tt = LUA_VTHREAD;
   g->currentwhite = bitmask(WHITE0BIT);
   L->marked = luaC_white(g);
@@ -368,7 +348,6 @@ LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud, unsigned seed) {
   g->ud = ud;
   g->warnf = NULL;
   g->ud_warn = NULL;
-  g->mainthread = L;
   g->seed = seed;
   g->gcstp = GCSTPGC;  /* no GC while building state */
   g->strt.size = g->strt.nuse = 0;
@@ -386,7 +365,7 @@ LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud, unsigned seed) {
   g->gray = g->grayagain = NULL;
   g->weak = g->ephemeron = g->allweak = NULL;
   g->twups = NULL;
-  g->GCtotalbytes = sizeof(LG);
+  g->GCtotalbytes = sizeof(global_State);
   g->GCmarked = 0;
   g->GCdebt = 0;
   setivalue(&g->nilvalue, 0);  /* to signal that state is not yet built */
@@ -408,7 +387,7 @@ LUA_API lua_State *lua_newstate (lua_Alloc f, void *ud, unsigned seed) {
 
 LUA_API void lua_close (lua_State *L) {
   lua_lock(L);
-  L = G(L)->mainthread;  /* only the main thread can be closed */
+  L = mainthread(G(L));  /* only the main thread can be closed */
   close_state(L);
 }
 

lstate.h

@@ -283,6 +283,48 @@ struct CallInfo {
 #define getoah(ci)  (((ci)->callstatus & CIST_OAH) ? 1 : 0)
 
 
+/*
+** 'per thread' state
+*/
+struct lua_State {
+  CommonHeader;
+  lu_byte allowhook;
+  TStatus status;
+  unsigned short nci;  /* number of items in 'ci' list */
+  StkIdRel top;  /* first free slot in the stack */
+  struct global_State *l_G;
+  CallInfo *ci;  /* call info for current function */
+  StkIdRel stack_last;  /* end of stack (last element + 1) */
+  StkIdRel stack;  /* stack base */
+  UpVal *openupval;  /* list of open upvalues in this stack */
+  StkIdRel tbclist;  /* list of to-be-closed variables */
+  GCObject *gclist;
+  struct lua_State *twups;  /* list of threads with open upvalues */
+  struct lua_longjmp *errorJmp;  /* current error recover point */
+  CallInfo base_ci;  /* CallInfo for first level (C host) */
+  volatile lua_Hook hook;
+  ptrdiff_t errfunc;  /* current error handling function (stack index) */
+  l_uint32 nCcalls;  /* number of nested non-yieldable or C calls */
+  int oldpc;  /* last pc traced */
+  int basehookcount;
+  int hookcount;
+  volatile l_signalT hookmask;
+  struct {  /* info about transferred values (for call/return hooks) */
+    int ftransfer;  /* offset of first value transferred */
+    int ntransfer;  /* number of values transferred */
+  } transferinfo;
+};
+
+
+/*
+** thread state + extra space
+*/
+typedef struct LX {
+  lu_byte extra_[LUA_EXTRASPACE];
+  lua_State l;
+} LX;
+
+
 /*
 ** 'global state', shared by all threads of this state
 */
@@ -324,50 +366,18 @@ typedef struct global_State {
   GCObject *finobjrold;  /* list of really old objects with finalizers */
   struct lua_State *twups;  /* list of threads with open upvalues */
   lua_CFunction panic;  /* to be called in unprotected errors */
-  struct lua_State *mainthread;
   TString *memerrmsg;  /* message for memory-allocation errors */
   TString *tmname[TM_N];  /* array with tag-method names */
   struct Table *mt[LUA_NUMTYPES];  /* metatables for basic types */
   TString *strcache[STRCACHE_N][STRCACHE_M];  /* cache for strings in API */
   lua_WarnFunction warnf;  /* warning function */
   void *ud_warn;         /* auxiliary data to 'warnf' */
+  LX mainth;  /* main thread of this state */
 } global_State;
 
 
-/*
-** 'per thread' state
-*/
-struct lua_State {
-  CommonHeader;
-  lu_byte allowhook;
-  TStatus status;
-  unsigned short nci;  /* number of items in 'ci' list */
-  StkIdRel top;  /* first free slot in the stack */
-  global_State *l_G;
-  CallInfo *ci;  /* call info for current function */
-  StkIdRel stack_last;  /* end of stack (last element + 1) */
-  StkIdRel stack;  /* stack base */
-  UpVal *openupval;  /* list of open upvalues in this stack */
-  StkIdRel tbclist;  /* list of to-be-closed variables */
-  GCObject *gclist;
-  struct lua_State *twups;  /* list of threads with open upvalues */
-  struct lua_longjmp *errorJmp;  /* current error recover point */
-  CallInfo base_ci;  /* CallInfo for first level (C host) */
-  volatile lua_Hook hook;
-  ptrdiff_t errfunc;  /* current error handling function (stack index) */
-  l_uint32 nCcalls;  /* number of nested non-yieldable or C calls */
-  int oldpc;  /* last pc traced */
-  int basehookcount;
-  int hookcount;
-  volatile l_signalT hookmask;
-  struct {  /* info about transferred values (for call/return hooks) */
-    int ftransfer;  /* offset of first value transferred */
-    int ntransfer;  /* number of values transferred */
-  } transferinfo;
-};
-
-
 #define G(L)	(L->l_G)
+#define mainthread(G)	(&(G)->mainth.l)
 
 /*
 ** 'g->nilvalue' being a nil value flags that the state was completely

ltests.c

@@ -408,7 +408,7 @@ static void checktable (global_State *g, Table *h) {
   for (n = gnode(h, 0); n < limit; n++) {
     if (!isempty(gval(n))) {
       TValue k;
-      getnodekey(g->mainthread, &k, n);
+      getnodekey(mainthread(g), &k, n);
       assert(!keyisnil(n));
       checkvalref(g, hgc, &k);
       checkvalref(g, hgc, gval(n));
@@ -672,7 +672,7 @@ int lua_checkmemory (lua_State *L) {
   l_mem totalin;  /* total of objects that are in gray lists */
   l_mem totalshould;  /* total of objects that should be in gray lists */
   if (keepinvariant(g)) {
-    assert(!iswhite(g->mainthread));
+    assert(!iswhite(mainthread(g)));
     assert(!iswhite(gcvalue(&g->l_registry)));
   }
   assert(!isdead(g, gcvalue(&g->l_registry)));