EDIT: I've not found any way to safely terminate LuaJ's threads without modifying LuaJ itself. The following was what I came up with, though it doesn't work with LuaJ. However, it can be easily modified to do its job in pure Lua. I may be switching to a Python binding for Java since LuaJ threading is so problematic.
--- I came up with the following, but it doesn't work with LuaJ ---
Here is a possible solution. I register a hook with debug.sethook that gets triggered on "count" events (these events occur even in a while true do end). I also pass a custom "ScriptState" Java object I created which contains a boolean flag indicating whether the script should terminate or not. The Java object is queried in the Lua hook which will throw an error to close the script if the flag is set (edit: throwing an error doesn't actually terminate the script). The terminate flag may also be set from inside the Lua script.
If you wish to automatically terminate unyielding infinite loops, it's straightforward enough to implement a timer system which records the last time a call was made to the ScriptState, then automatically terminate the script if sufficient time passes without an API call (edit: this only works if the thread can be interrupted). If you want to kill infinite loops but not interrupt certain blocking operations, you can adjust the ScriptState object to include other state information that allows you to temporarily pause auto-termination, etc.
Here is my interpreter.lua which can be used to call another script and interrupt it if/when necessary. It makes calls to Java methods so it will not run without LuaJ (or some other Lua-Java library) unless it's modified (edit: again, it can be easily modified to work in pure Lua).
function hook_line(e)
if jthread:getDone() then
-- I saw someone else use error(), but an infinite loop still seems to evade it.
-- os.exit() seems to take care of it well.
os.exit()
end
end
function inithook()
-- the hook will run every 100 million instructions.
-- the time it takes for 100 million instructions to occur
-- is based on computer speed and the calling environment
debug.sethook(hook_line, "", 1e8)
local ret = dofile(jLuaScript)
debug.sethook()
return ret
end
args = { ... }
if jthread == nil then
error("jthread object is nil. Please set it in the Java environment.",2)
elseif jLuaScript == nil then
error("jLuaScript not set. Please set it in the Java environment.",2)
else
local x,y = xpcall(inithook, debug.traceback)
end
Here's the ScriptState class that stores the flag and a main() to demonstrate:
public class ScriptState {
private AtomicBoolean isDone = new AtomicBoolean(true);
public boolean getDone() { return isDone.get(); }
public void setDone(boolean v) { isDone.set(v); }
public static void main(String[] args) {
Thread t = new Thread() {
public void run() {
System.out.println("J: Lua script started.");
ScriptState s = new ScriptState();
Globals g = JsePlatform.debugGlobals();
g.set("jLuaScript", "res/main.lua");
g.set("jthread", CoerceJavaToLua.coerce(s));
try {
g.loadFile("res/_interpreter.lua").call();
} catch (Exception e) {
System.err.println("There was a Lua error!");
e.printStackTrace();
}
}
};
t.start();
try { t.join(); } catch (Exception e) { System.err.println("Error waiting for thread"); }
System.out.println("J: End main");
}
}
res/main.lua contains the target Lua code to be run. Use environment variables or parameters to pass additional information to the script as usual. Remember to use JsePlatform.debugGlobals() instead of JsePlatform.standardGlobals() if you want to use the debug library in Lua.
EDIT: I just noticed that os.exit() not only terminates the Lua script but also the calling process. It seems to be the equivalent of System.exit(). error() will throw an error but will not cause the Lua script to terminate. I'm trying to find a solution for this now.
