How to interrupt running Lua

script.lua

local x = 0
for i = 1, 10000000000 do
    local y = getNumber() -- C function
    x = x + y
end
print(x)

wrapper.cpp

// C++11
// Compile on Debian Wheezy:
// g++ -std=c++11 wrapper.cpp -o wrapper.exe \
//    -llua5.1 -I /usr/include/lua5.1/ -pthread

#include <cstdlib>
#include <cstdio>
#include <ctime>
#include <thread>

#include <lua.hpp>

bool stop_lua = false;

int getNumber(lua_State* L) {
    if (stop_lua) {
        return luaL_error(L, "Interrupted");
    }
    // return random number
    int value = std::rand();
    lua_pushinteger(L, value);
    return 1;
}

void luaRunner() {
    // this code is run in other thread
    lua_State* L = luaL_newstate();
    luaL_openlibs(L);
    // bind function getGlobal
    lua_pushcfunction(L, getNumber);
    lua_setglobal(L, "getNumber");
    // run script.lua
    int error = luaL_dofile(L, "script.lua");
}

int main() {
    std::srand(std::time(NULL));
    std::thread thread(luaRunner);
    printf("Lua works in other thread\n");
    while (true) {
        printf("Type 123 to interrupt Lua.\n");
        int input;
        scanf("%d", &input);
        if (input == 123) {
            stop_lua = true;
            printf("Lua stopped!.\n");
        }
    }
}

nice code.

Question from a new lua coder: this code can interrupt the lua executor and stop the program.
Does lua support to interrupt lua, save the lua state, then we restore lua exactly at the point where last time it get inpterrupted?

Thanks,
etorth

nice code.

Question from a new lua coder: this code can interrupt the lua executor and stop the program.
Does lua support to interrupt lua, save the lua state, then we restore lua exactly at the point where last time it get inpterrupted?

Thanks,
etorth

Hey etorth

Yes it does, through yield. It has to be cooperative rather than preemptive anyway.

Boris

Nice idea!

But as a side-note for other readers signaling another thread this way is unsafe (it's not guaranteed that stop_lua will ever read the changed value in the "luaRunner" thread, for example, because CPU caches are never synchronized).
The simplest way would be using an std::atomic.