[VM] Smarter Idle with Scheduler

Most objects in a lot are completely inanimate, eg. windows, doors, chairs, counters, but still perform a full VM tick every frame. This tick usually consists of initializing the execution context, checking to see if it is valid, checking interaction status, finding the top stack frame, getting the current instruction & its handler, running the Sleep primitive to poll for interrupts and decrement the parameter (one of the 20000 ticks the object wants to sleep for), handling its return value and then doing a few other checks and background operations that really could be skipped for most objects.

I would say over 90% of objects in most lots have a main method that is literally just "idle 20000 ticks", as the objects do not need to animate or do any kind of internal polling. The tick function also performs some operations to do with currently playing sounds and headlines, which are in an even smaller minority, yet are currently run constantly on every object. It is only important to run entity and thread ticks every frame on avatars.

The solution would be to implement a "schedule", where the VM would only run ticks on the objects that have been "scheduled" to continue executing on that frame, instead of all of them. The thread would be extended to include an internal timer to indicate how long it has been dormant for, so time sensitive variables can be updated accordingly. For example, an object entering idle for "20000 ticks" would schedule itself to run again on tick (current + 20000). If it is interrupted out of idle by another object, this registration should be moved to (newCurrent + 1) to execute as soon as possible. Its "Tick()" function would never even be touched for the frames where it is not scheduled, saving execution time.

When idling in freeso.ml, VMEntity ticks take ~79% of the internal tick's execution time. If we could strip out this theoretical 90%, that's an easy 3.5x speedup for idle lots. This would make it a lot easier to host lots on the MMO server, and a little easier to run on slower devices. The bottleneck would quickly become the renderer. (yes, even more than it is now)

Things which need to be considered:

Thread interrupts must be direct. These must also update the parameter we were waiting on.
An implementation would assume that no objects would change another object's current thread Args[] (used to keep track of sleep duration), and true enough there is not a way to do this.
VMGameObject does per-tick checking on pending roommate deletion and object limit exceeded.
"LockoutCount" variable will need to be lazily evaluated on request from the last tick it was set.
Objects with active sounds will need to tick them regardless. These are also a minority.
Objects with headlines are a similar case. May wish to rethink their render path entirely.
ALL internal frame counters must be replaced/suplemented with a "last set" timestamp against a global tick clock.
Ordering and synchronisation. If it's reliable enough, the schedule will not have to be sent with the VM state to maintain synchro, but it might be quite difficult to get it working this reliably.

riperiperi / FreeSO

[VM] Smarter Idle with Scheduler #33