Resume lua main thread

resumemainthread.c

#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <stdio.h>

const char * source = "print 'A' ; coroutine.yield() ; print 'B'";

int
main() {
	lua_State *L = luaL_newstate();
	luaL_openlibs(L);
	luaL_loadstring(L, source);
	printf("step 1\n");
	int r;
	lua_resume(L, NULL, 0, &r);
	printf("step 2\n");
	lua_resume(L, NULL, 0, &r);
	lua_close(L);
	return 0;
}