Lua Add Emergency Garbage Collector

Derivative of work by RobertGabrielJakabosky
 http://lua-users.org/wiki/EmergencyGarbageCollector

I've only implemented the not enough memory part and
 expanded this idea to adding a mechanism to signal
 the OOM condition of the plugin buffer which allows us to only
 grab the playback buffer after garbage collection fails
 (SO THE MUSIC KEEPS PLAYING AS LONG AS POSSIBLE)

Change-Id: I684fb98b540ffc01f7ba324ab5b761ceb59b9f9b

1 files changed, 18 insertions, 3 deletions

diff --git a/apps/plugins/lua/ldo.c b/apps/plugins/lua/ldo.c
index 43266de95e..7eccc54480 100644
--- a/apps/plugins/lua/ldo.c
+++ b/apps/plugins/lua/ldo.c
@@ -51,11 +51,13 @@ struct lua_longjmp {
 void luaD_seterrorobj (lua_State *L, int errcode, StkId oldtop) {
   switch (errcode) {
     case LUA_ERRMEM: {
-      setsvalue2s(L, oldtop, luaS_newliteral(L, MEMERRMSG));
+      ptrdiff_t oldtopr = savestack(L, oldtop);
+      setsvalue2s(L, restorestack(L, oldtopr), luaS_newliteral(L, MEMERRMSG));
       break;
     }
     case LUA_ERRERR: {
-      setsvalue2s(L, oldtop, luaS_newliteral(L, "error in error handling"));
+      ptrdiff_t oldtopr = savestack(L, oldtop);
+      setsvalue2s(L, restorestack(L, oldtopr), luaS_newliteral(L, "error in error handling"));
       break;
     }
     case LUA_ERRSYNTAX:
@@ -92,6 +94,8 @@ static void resetstack (lua_State *L, int status) {
 
 
 void luaD_throw (lua_State *L, int errcode) {
+  unfixedstack(L); /* make sure the fixedstack & block_gc flags get reset. */
+  unset_block_gc(L);
   if (L->errorJmp) {
     L->errorJmp->status = errcode;
     LUAI_THROW(L, L->errorJmp);
@@ -208,7 +212,9 @@ void luaD_callhook (lua_State *L, int event, int line) {
 static StkId adjust_varargs (lua_State *L, Proto *p, int actual) {
   int i;
   int nfixargs = p->numparams;
+#if defined(LUA_COMPAT_VARARG)
   Table *htab = NULL;
+#endif
   StkId base, fixed;
   for (; actual < nfixargs; ++actual)
     setnilvalue(L->top++);
@@ -219,10 +225,15 @@ static StkId adjust_varargs (lua_State *L, Proto *p, int actual) {
     luaC_checkGC(L);
     luaD_checkstack(L, p->maxstacksize);
     htab = luaH_new(L, nvar, 1);  /* create `arg' table */
+    sethvalue2s(L, L->top, htab); /* put table on stack */
+    incr_top(L);
+    fixedstack(L);
     for (i=0; i<nvar; i++)  /* put extra arguments into `arg' table */
-      setobj2n(L, luaH_setnum(L, htab, i+1), L->top - nvar + i);
+      setobj2n(L, luaH_setnum(L, htab, i+1), L->top - 1 - nvar + i);
+    unfixedstack(L);
     /* store counter in field `n' */
     setnvalue(luaH_setstr(L, htab, luaS_newliteral(L, "n")), cast_num(nvar));
+    L->top--; /* remove table from stack */
   }
 #endif
   /* move fixed parameters to final position */
@@ -232,11 +243,13 @@ static StkId adjust_varargs (lua_State *L, Proto *p, int actual) {
     setobjs2s(L, L->top++, fixed+i);
     setnilvalue(fixed+i);
   }
+#if defined(LUA_COMPAT_VARARG)
   /* add `arg' parameter */
   if (htab) {
     sethvalue(L, L->top++, htab);
     lua_assert(iswhite(obj2gco(htab)));
   }
+#endif
   return base;
 }
 
@@ -495,6 +508,7 @@ static void f_parser (lua_State *L, void *ud) {
   struct SParser *p = cast(struct SParser *, ud);
   int c = luaZ_lookahead(p->z);
   luaC_checkGC(L);
+  set_block_gc(L);  /* stop collector during parsing */
   tf = ((c == LUA_SIGNATURE[0]) ? luaU_undump : luaY_parser)(L, p->z,
                                                              &p->buff, p->name);
   cl = luaF_newLclosure(L, tf->nups, hvalue(gt(L)));
@@ -503,6 +517,7 @@ static void f_parser (lua_State *L, void *ud) {
     cl->l.upvals[i] = luaF_newupval(L);
   setclvalue(L, L->top, cl);
   incr_top(L);
+  unset_block_gc(L);
 }