The latest version of Cobalt has several major changes, which I'm
looking forward to taking advantage of in the coming months:
- The Lua interpreter has been split up from the actual LuaClosure
instance. It now runs multiple functions within one loop, handling
pushing/popping and resuming method calls correctly.
This means we have a theoretically infinite call depth, as we're no
longer bounded by Java's stack size. In reality, this is limited to
32767 (Short.MAX_VALUE), as that's a mostly equivalent to the limits
PUC Lua exposes.
- The stack is no longer unwound in the event of errors. This both
simplifies error handling (not that CC:T needs to care about that)
but also means one can call debug.traceback on a now-dead coroutine
(which is more useful for debugging than using xpcall).
- Most significantly, coroutines are no longer each run on a dedicated
thread. Instead, yielding or resuming throws an exception to unwind
the Java stack and switches to a different coroutine.
In order to preserve compatability with CC's assumption about LuaJ's
threading model (namely that yielding blocks the thread), we also
provide a yieldBlock method (which CC:T consumes). This suspends the
current thread and switches execution to a new thread (see
SquidDev/Cobalt@b5ddf164f1 for more
details). While this does mean we need to use more than 1 thread,
it's still /substantially/ less than would otherwise be needed.
We've been running these changes on SwitchCraft for a few days now and
haven't seen any issues. One nice thing to observe is that the number of
CC thread has gone down from ~1.9k to ~100 (of those, ~70 are dedicated
to running coroutines). Similarly, the server has gone from generating
~15k threads over its lifetime, to ~3k. While this is still a lot, it's
a substantial improvement.
- Remove a redundant logger
- Provide a getter for the ComputerCraft thread group. This allows us
to monitor child threads within prometheus.
- Replace a deprecated call with a fastutils alternative.
- Keep track of the number of created and destroyed coroutines for each
computer.
- Run coroutines with a thread pool executor, which will keep stale
threads around for 60 seconds. This substantially reduces the
pressure from short-lived coroutines.
- Update to the latest Cobalt version.
Whilst I'm pretty sure this is safe for general use, I'm disabling this
by default for now. I may consider enabling it in the future if no
issues are found.
