Summary

This is a fully functional alternative to XEngine for LSL/OSSL scripts, featuring

• Preemptive Multitasking
• Improved script syntax
• Memory heap and stack use control per script
• Optional 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.
The released execution thread goes on processing other scripts.
A script event can run for about 60ms until releasing execution. 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() and other internal script sleeps. On YEngine, this just release execution and wait in a queue, until the sleep time expires. On XEngine a "expensive" execution thread was placed in Sleep mode, so not available to do anything.

Improved script syntax

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

if(oneKey)
   ...

should now work.

llSomething; // missing()
break; // but see new extensions

are now errors

complex statements execution order may be different from XEngine. One should always use (..) to enforce it the wanted order! (and in any language)

New language extensions

If the first or second line of a script is (first line can still be script engine and language selection)

yoptions;

Yengine specific language extensions are activated

• switch
• break
• continue
• try catch and finally

Scripts using this features will not compile or run on XEngine.

Memory heap and stack use control

Yengine keeps control of the memory a script uses.
There are two types of memory:

• Stack holds function arguments and simple local variables.
  
• Heap holds global variables and complex variables like lists or strings, even if they are local to a method/event.
  

the maximum values a script can use can be configured in OpenSim.Ini section [YEngine]

; maximum stack a script can use in KB
;ScriptStackSize = 2048
   
; maximum heap memory a script can use in KB
;ScriptHeapSize = 1024

you may need to increase this values

Activation

Opensimulator 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.

Configuration

Please see file OpenSimDefaults.ini, section [YEngine] for details.
Like on all case, if you need to change something, copy respective lines to similar location on file OpenSim.ini, and change there

Origins

YEngine is a modified derivative of XMREngine
XMREngine was used and developed by teams of DreamNation and Avination grids. With early work from Meta
It is still in used by DreamNation
http://wiki.dreamnation.net/index.php/XMREngine_Script_Engine