commit d39ea8b3ce684728c1ad5005192766d39d2e8baa
author Roberto Ierusalimschy <roberto@inf.puc-rio.br> Mon Jul 06 13:54:01 2020 -0300
committer Roberto Ierusalimschy <roberto@inf.puc-rio.br> Mon Jul 06 13:54:01 2020 -0300
tree a6366af9c0fb14af5b244b609cbc3da2b652b798
parent 6298903e35217ab69c279056f925fb72900ce0b7

Make sure that main thread is non yieldable

Main thread must be non yieldable even at "level 0" (bare API), outside
the 'pcall' from 'lua.c'.

lstate.c

diff --git a/lstate.c b/lstate.c
index 4434211..b1f487f 100644
--- a/lstate.c
+++ b/lstate.c
@@ -395,6 +395,7 @@
   g->allgc = obj2gco(L);  /* by now, only object is the main thread */
   L->next = NULL;
   g->Cstacklimit = L->nCcalls = LUAI_MAXCSTACK + CSTACKERR;
+  incnny(L);  /* main thread is always non yieldable */
   g->frealloc = f;
   g->ud = ud;
   g->warnf = NULL;

ltests.c

diff --git a/ltests.c b/ltests.c
index 164b5a2..0513354 100644
--- a/ltests.c
+++ b/ltests.c
@@ -145,7 +145,6 @@
         lua_pushstring(L, buff);
         lua_setglobal(L, "_WARN");  /* assign message to global '_WARN' */
         lua_lock(L);
-        buff[0] = '\0';  /* prepare buffer for next warning */
         break;
       }
     }
@@ -749,11 +748,12 @@
 static void printstack (lua_State *L) {
   int i;
   int n = lua_gettop(L);
+  printf("stack: >>\n");
   for (i = 1; i <= n; i++) {
     printf("%3d: %s\n", i, luaL_tolstring(L, i, NULL));
     lua_pop(L, 1);
   }
-  printf("\n");
+  printf("<<\n");
 }
 
 
@@ -1678,6 +1678,9 @@
       if (n == 0) n = lua_gettop(fs);
       lua_xmove(fs, ts, n);
     }
+    else if EQ("isyieldable") {
+      lua_pushboolean(L1, lua_isyieldable(lua_tothread(L1, getindex)));
+    }
     else if EQ("yield") {
       return lua_yield(L1, getnum);
     }

testes/coroutine.lua

diff --git a/testes/coroutine.lua b/testes/coroutine.lua
index 0a4c2ef..955f677 100644
--- a/testes/coroutine.lua
+++ b/testes/coroutine.lua
@@ -407,7 +407,8 @@
 
 
 if not T then
-  (Message or print)('\n >>> testC not active: skipping yield/hook tests <<<\n')
+  (Message or print)
+      ('\n >>> testC not active: skipping coroutine API tests <<<\n')
 else
   print "testing yields inside hooks"
 
@@ -564,8 +565,17 @@
          c == "ERRRUN" and d == 4)
 
 
-  -- using a main thread as a coroutine
+  -- using a main thread as a coroutine  (dubious use!)
   local state = T.newstate()
+
+  -- check that yielddable is working correctly
+  assert(T.testC(state, "newthread; isyieldable -1; remove 1; return 1"))
+
+  -- main thread is not yieldable
+  assert(not T.testC(state, "rawgeti R 1; isyieldable -1; remove 1; return 1"))
+
+  T.testC(state, "settop 0")
+
   T.loadlib(state)
 
   assert(T.doremote(state, [[