Re: Multithreading lua scripts from C

[Milind Gupta <milind.gupta@...>]

Hi,

        Thanks for your reply. My intention is to create 2 totally independent lua scripts running in parallel. So I run them in completely separate Lua States since I don't want their global space to overlap.

        I figured out that I was never yielding from the coroutine so I fixed my code like this which is working good. So now I want to write a module in C which when called from Lua would allow the lua program to run multiple lua scripts simultaneously without needing any support from the OS.

My program now is:

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

int flag = 0;
lua_State *luaVM1, *luaVM2, *thread1, *thread2;
int hookFunc(lua_State *L, lua_Debug *dbg);

int main(int argc, char* argv[ ])
{
    luaVM1 = luaL_newstate();
    luaVM2 = luaL_newstate();

    luaL_openlibs(luaVM1);
    luaL_openlibs(luaVM2);

    thread1 = lua_newthread(luaVM1);
    thread2 = lua_newthread(luaVM2);

    if (NULL == luaVM1 || NULL == luaVM2)
   {
      printf("Error Initializing lua\n");
      return -1;
   }
   char* prog1 = "for i = 1,5 do print('x'..tostring(i)) end";
   char* prog2 = "for i = 1,10 do print('y'..tostring(i)) end";
   // Create threads in each lua state
   // Now push the function into the stack of each thread
   luaL_loadstring(thread1,prog1);
   luaL_loadstring(thread2,prog2);
   lua_sethook(thread1,(lua_Hook) hookFunc,LUA_MASKCOUNT,4);
   lua_sethook(thread2,(lua_Hook) hookFunc,LUA_MASKCOUNT,4);

   lua_resume(thread1,0);
   flag=1;
   lua_resume(thread2,0);
   while(lua_status(thread1) || lua_status(thread2))
   {
       if (flag==0)
       {
           flag = 1;
           if (lua_status(thread2))
               lua_resume(thread2,0);
       }
       else
       {
           flag = 0;
           if (lua_status(thread1))
               lua_resume(thread1,0);
       }
   }


   lua_close( luaVM1 );
   lua_close( luaVM2 );
 
   return 0;
}

int hookFunc(lua_State *L, lua_Debug *dbg)
{
    printf("Hook Called\n");
    if(flag==0)
    {
        printf("Flag0\n");
        return lua_yield(thread1,0);
    }
    else
    {
        printf("flag1\n");
        return lua_yield(thread2,0);
    }
    return 0;
}

On Tue, Feb 18, 2014 at 11:50 PM, Tim Hill <drtimhill@gmail.com> wrote:

On Feb 18, 2014, at 11:19 PM, Milind Gupta <milind.gupta@gmail.com> wrote:

> Hi,
>         I attempted at running multiple lua scripts from C. Pasted below is the code I have. The 2 lua scripts are in the strings prog1 and prog2 which are basically 2 unequal loops. I create threads and set hooks for the thread for a mask count of 4. I resume each alternately but I do not get the expected result at all. I never see an output from prog2 and prog1 i somehow becomes a decimal number. The output is as follows:
>

> And the program is as follows:
>
>

> int main(int argc, char* argv[ ])
> {
>     luaVM1 = lua_open();
>     luaVM2 = lua_open();
>
>     luaL_openlibs(luaVM1);
>     luaL_openlibs(luaVM2);
>
>     thread1 = lua_newthread(luaVM1);
>     thread2 = lua_newthread(luaVM2);
>

lua_open() (which is really just lua_newstate() under it’s old name) creates both an independent Lua state *and* it’s first thread. If you want coroutines *within* that state you should use lua_newthread() to create the additional threads. So call lua_newstate() once and lua_newthread() once.

lua_open()/lua_newstate() create brand-new, independent Lua states that do not share anything (not even globals or the GC state). lua_newthread() adds another thread to an existing Lua state in the same way lua_newtable() adds a new table.

—Tim