Help with pre-emptive multithreading

Actually cooperative multitasking is a lot more sensible than you think.

Ok, it got a bad press from things like Windows 3 and Macos < 10, but it's really ideal. Sensible operating systems with well controlled tasks which used it rarely had problems (Netware, anyone?)

The only reason we need preemptive multitasking is because our programs don't always cooperate.

If you wrote all the scripts yourself, you know that they're going to yield in ample time.

Specificially, if you have scripts for controlling (for example) NPCs, these will usually look like:

// NPC code for NPC "bob"get out of bed;walk to door;open door;leave; close door;go to field;until (hometime) {  work in field;}// etc

Those subroutines themselves, will all be of the basic form:

Trigger the beginning of some action;wait for it to become complete;

It is this second part "wait for it to become complete" which will do the yielding.

Your script need not explicitly yield anywhere, as long as it's always going to be in a loop calling something which always yields. This is not difficult to achieve.

Then in your native code, you can have something which checks whether the current action is complete, and if it is, calls resume() on the coroutine which called yield().

I've tested this idea and it seems to work fine.

Mark

Thanks!

When reading the Lua manual, I had only noticed the functions to use yield and resume from within the script. Now I've noticed that there are equivalent functions that can be used with the API from within C.

You can't yield from the middle of C code. But I believe you can yield from a C function called from lua, as it returns.

You can of course resume coroutines from inside C code.

To make things easier, in my example I explicitly used yield() in the lua code. You'd do this in your library subroutines though, not in your NPC code.

Here is my code. This makes the NPC ("me") go to 42,99. walkTo() is a native (C++) method on the "me" object. hasArrived() returns a boolean.

function actions(me)         me:walkTo(42,99)        while (not me:hasArrived()) do          print("Not there yet")          coroutine.yield()        end        print("Yay, got there")end

Mark