Summary

This is a fully functional alternative to XEngine.

• Preemptive Multitasking
• Improved script syntax
• New language extensions

Preemptive Multitasking

YEngine executes script events using preemptive multitasking.
This means that, at certain control points or when told, a script may release execution, waiting in a queue until it is its turn to execute again.
A script event can run for about 60ms before placed in queue, then on continuations it can run for about 30ms. (This times may change)
The script can also be placed in a sleep state until a sleep time elapses.
This, for example, solves one of XEngine worse problems: llSleep(). llSleep just places the script on a wait queue, until the sleep time expires, using no other execution resources

Improved script syntax

YEngine follows more closely LSL script syntax and execution order. statements like

if(oneKey)
   ...

should now work

New language extensions

Activation

Opensimulation default configuration selects XEngine. To change to YEngine you need to change OpenSim.ini:
[Startup] section:

DefaultScriptEngine = "YEngine"

[Yengine] section:

Enable = true

[Xengine] section:

Enable = false

Note: in theory, opensimulator could run several engines at same time, but we should not do that with X and Y engines.