From 1bd70a8e40a8600658c706d5f171138e9b902aba Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Thu, 8 May 2014 10:52:20 -0300
Subject: [PATCH] new function 'lua_isyieldable' (and 'coroutine.isyieldable')

---
 lcorolib.c | 22 +++++++++++++++++-----
 ldo.c      |  7 ++++++-
 lua.h      |  4 +++-
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/lcorolib.c b/lcorolib.c
index cd7e4e1e..4bcb7e9a 100644
--- a/lcorolib.c
+++ b/lcorolib.c
@@ -1,5 +1,5 @@
 /*
-** $Id: lcorolib.c,v 1.4 2012/04/27 18:59:04 roberto Exp roberto $
+** $Id: lcorolib.c,v 1.5 2013/02/21 13:44:53 roberto Exp roberto $
 ** Coroutine Library
 ** See Copyright Notice in lua.h
 */
@@ -17,6 +17,13 @@
 #include "lualib.h"
 
 
+static lua_State *getco (lua_State *L) {
+  lua_State *co = lua_tothread(L, 1);
+  luaL_argcheck(L, co, 1, "coroutine expected");
+  return co;
+}
+
+
 static int auxresume (lua_State *L, lua_State *co, int narg) {
   int status;
   if (!lua_checkstack(co, narg)) {
@@ -47,9 +54,8 @@ static int auxresume (lua_State *L, lua_State *co, int narg) {
 
 
 static int luaB_coresume (lua_State *L) {
-  lua_State *co = lua_tothread(L, 1);
+  lua_State *co = getco(L);
   int r;
-  luaL_argcheck(L, co, 1, "coroutine expected");
   r = auxresume(L, co, lua_gettop(L) - 1);
   if (r < 0) {
     lua_pushboolean(L, 0);
@@ -102,8 +108,7 @@ static int luaB_yield (lua_State *L) {
 
 
 static int luaB_costatus (lua_State *L) {
-  lua_State *co = lua_tothread(L, 1);
-  luaL_argcheck(L, co, 1, "coroutine expected");
+  lua_State *co = getco(L);
   if (L == co) lua_pushliteral(L, "running");
   else {
     switch (lua_status(co)) {
@@ -129,6 +134,12 @@ static int luaB_costatus (lua_State *L) {
 }
 
 
+static int luaB_yieldable (lua_State *L) {
+  lua_pushboolean(L, lua_isyieldable(L));
+  return 1;
+}
+
+
 static int luaB_corunning (lua_State *L) {
   int ismain = lua_pushthread(L);
   lua_pushboolean(L, ismain);
@@ -143,6 +154,7 @@ static const luaL_Reg co_funcs[] = {
   {"status", luaB_costatus},
   {"wrap", luaB_cowrap},
   {"yield", luaB_yield},
+  {"isyieldable", luaB_yieldable},
   {NULL, NULL}
 };
 
diff --git a/ldo.c b/ldo.c
index 267c8237..ae58cda7 100644
--- a/ldo.c
+++ b/ldo.c
@@ -1,5 +1,5 @@
 /*
-** $Id: ldo.c,v 2.114 2014/02/26 15:27:56 roberto Exp roberto $
+** $Id: ldo.c,v 2.115 2014/03/21 13:52:33 roberto Exp roberto $
 ** Stack and Call structure of Lua
 ** See Copyright Notice in lua.h
 */
@@ -571,6 +571,11 @@ LUA_API int lua_resume (lua_State *L, lua_State *from, int nargs) {
 }
 
 
+LUA_API int lua_isyieldable (lua_State *L) {
+  return (L->nny == 0);
+}
+
+
 LUA_API int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k) {
   CallInfo *ci = L->ci;
   luai_userstateyield(L, nresults);
diff --git a/lua.h b/lua.h
index bef5ff29..464d3717 100644
--- a/lua.h
+++ b/lua.h
@@ -1,5 +1,5 @@
 /*
-** $Id: lua.h,v 1.303 2014/05/01 18:18:06 roberto Exp roberto $
+** $Id: lua.h,v 1.304 2014/05/01 18:21:32 roberto Exp roberto $
 ** Lua - A Scripting Language
 ** Lua.org, PUC-Rio, Brazil (http://www.lua.org)
 ** See Copyright Notice at the end of this file
@@ -282,6 +282,8 @@ LUA_API int  (lua_yieldk) (lua_State *L, int nresults, int ctx,
 #define lua_yield(L,n)		lua_yieldk(L, (n), 0, NULL)
 LUA_API int  (lua_resume) (lua_State *L, lua_State *from, int narg);
 LUA_API int  (lua_status) (lua_State *L);
+LUA_API int lua_isyieldable (lua_State *L);
+
 
 /*
 ** garbage-collection function and options