When would one want to use $KERNEL.Singletons?

Hello all oscript wizards:Following on from my previous post where I was trying to find a way to find a thread-shared application global (not really possible or advisable I'm told):I fail to see under which circumstances one would want to make use of $KERNEL.Singletons?(In case you missed it - the singleton isn't shared across threads unfortunately.)I guess it could become a useful container if you have a lot of data that you want to store in separate Assocs, but all in a single global.The current single implementation of a Singleton seems to do this for WebNode cmds caching.Does it have anything to do with thread safety? Is this a deprecated feature that is actually just a hangover from previous functionality?Thanks,Rolf.(rolf@stasolutions.co.za)

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Jason_McPeak

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Rolf,

As you know, OScript is not a strongly typed language.

$Kernel.Singleton was one of the classes created to help us "think" in terms of modern programming practices; objects, patterns, etc. It was created to help us design better code.

$Kernel.Singleton is not thread safe.

$Kernel.Factory is another example. It's not currently used, but it's there.

As you could get from any pattern book, the singleton pattern is often used with the factory pattern to create a resource whose specific type is not known to the code that uses it.

Jason

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Subject: When would one want to use $KERNEL.Singletons?

When would one want to use $KERNEL.Singletons?

Posted by eu0018377 (Poser, Rolf H) on 03/12/2006 01:58 AM

Hello all oscript wizards:

Following on from my previous post where I was trying to find a way to find a thread-shared application global (not really possible or advisable I'm told):

I fail to see under which circumstances one would want to make use of $KERNEL.Singletons?

(In case you missed it - the singleton isn't shared across threads unfortunately.)

I guess it could become a useful container if you have a lot of data that you want to store in separate Assocs, but all in a single global.

The current single implementation of a Singleton seems to do this for WebNode cmds caching.

Does it have anything to do with thread safety?

Is this a deprecated feature that is actually just a hangover from previous functionality?

Thanks,
Rolf.
(rolf@stasolutions.co.za)

Rolf_Poser_(eu0018377_-_(deleted))

Jason:Thanks for the reply!So they're more of a curiosity than really useful for anything.. :-)I have a couple of questions on thread safety:1. Do you mean thread safety between livelink threads (or is this relative to some lightweight threading model that is implemented behind the scenes for each "thread")?2. If these functions are not thread safe between livelink threads, which functions should we be using? 3. Are module globals thread safe?Thanks,Rolf.

Jason_McPeak

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Sorry - wrong term; thread safety

I should let others who know more about this pipe in.

Basically the only thing I know is globals are not shared across threads. The only real way I know of to share data between threads is with the database. After all, you could be in a clustered environment.

Best thing I know to use; $LLIAPI.CacheUtil

Jason

From: eLink Discussion: Development Discussion [mailto:development@elinkkc.opentext.com]
Sent: Monday, March 13, 2006 11:28 AM
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Subject: Thread Safety?

Thread Safety?		Posted by eu0018377 (Poser, Rolf H) on 03/13/2006 12:27 PM
In reply to: RE When would one want to use $KERNEL.Singletons?		Posted by jmcpeak (McPeak, Jason) on 03/13/2006 10:34 AM

Jason:

Thanks for the reply!

So they're more of a curiosity than really useful for anything.. :-)

I have a couple of questions on thread safety:

1. Do you mean thread safety between livelink threads (or is this relative to some lightweight threading model that is implemented behind the scenes for each "thread")?
2. If these functions are not thread safe between livelink threads, which functions should we be using?
3. Are module globals thread safe?

Thanks,
Rolf.

Jonny_Coombes

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But the reality is that this pattern sucks, because then you move all the specific code into the factory, which in true software engineering style just moves the problem somewhere else. Then you come up with the abstract factory pattern which then dictates that a factory can create only objects from a specific base class, which then moves the problem somewhere else. (To the base, there is always a base)

All of this stuff is pretty abstract, and in the Oscript world not really that applicable, because at the end of the day: it is what is is, and doesn't do much more than that. Throughout the body of Oscript code born of many modules you'll find many aborted attempts at making it OO, none of which have worked, really.

It's just a reasonably well designed, procedural language - you can't dress it up as something that it ain't.

IMHO it would have been better to try and port this stuff to Javascript rather than Java, there are many more similarities. Then at least these kind of discussion threads wouldn't arise, wherein the fundamental reasons as to how/why/where you make Oscript truly OO are raised.

;0)

Jonny Coombes Bsc (Hons)
Principal Solutions Architect
Open Text Corporation

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Subject: RE When would one want to use $KERNEL.Singletons?

RE When would one want to use $KERNEL.Singletons? Posted by jmcpeak (McPeak, Jason) on 03/13/2006 10:34 AM
In reply to: When would one want to use $KERNEL.Singletons? Posted by eu0018377 (Poser, Rolf H) on 03/12/2006 01:58 AM

Message from Jason McPeak <JMcPeak@opentext.com> via eLink

Rolf, As you know, OScript is not a strongly typed language. $Kernel.Singleton was one of the classes created to help us "think" in terms of modern programming practices; objects, patterns, etc. It was created to help us design better code. $Kernel.Singleton is not thread safe. $Kernel.Factory is another example. It's not currently used, but it's there. As you could get from any pattern book, the singleton pattern is often used with the factory pattern to create a resource whose specific type is not known to the code that uses it. Jason
From: eLink Discussion: Development Discussion [mailto:development@elinkkc.opentext.com]
Sent: Sunday, March 12, 2006 1:01 AM
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Subject: When would one want to use $KERNEL.Singletons?

When would one want to use $KERNEL.Singletons? Posted by eu0018377 (Poser, Rolf H) on 03/12/2006 01:58 AM

Hello all oscript wizards:

Following on from my previous post where I was trying to find a way to find a thread-shared application global (not really possible or advisable I'm told):

I fail to see under which circumstances one would want to make use of $KERNEL.Singletons?

(In case you missed it - the singleton isn't shared across threads unfortunately.)

I guess it could become a useful container if you have a lot of data that you want to store in separate Assocs, but all in a single global.

The current single implementation of a Singleton seems to do this for WebNode cmds caching.

Does it have anything to do with thread safety?

Is this a deprecated feature that is actually just a hangover from previous functionality?

Thanks,
Rolf.
(rolf@stasolutions.co.za)

Rolf_Poser_(eu0018377_-_(deleted))

Jason:Thanks for the comment. I agree that the database is probably the better place to do this, but in my case I want extreme performance.I changed the design of my application to rather happily live unshared inside a singleton within each thread. The performance I'm seeking from my application (and now achieving) with regard to these operations must be in the order of microseconds rather than milliseconds. (around 300-400 microseconds currently). Will probably make this even faster once I've changed to a regular application global in stead of a singleton.As soon as you add a database call, you've acquired at least a 15ms delay (which is fine for most normal circumstances). :-)Regards,Rolf.