Re: How do service programs work ( Was: Service programs suck)

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

Most of your questions have already been discussed frequently in this  
list. I suggest you search the archives and also read the ILE  
Concepts manual. Other comments follow:


On 28/02/2008, at 10:02 PM, David FOXWELL wrote:

> OK, OK so I've never used a service program before and nor has  
> anyone else in our shop.

Then you should refrain from commenting and just question.

> I've done a little more reading and come up with this, please  
> someone correct me if I'm wrong.
>
> A program containing only modules is bound by copy and all the code  
> from all the modules is duplicated in one executable object.

True.

> When a service program is added, a reference is bound to the  
> program. The code is therefore not duplicated. The adress of this  
> code will be established at the first call of the procedure in the  
> service program.

Effectively true.

> Some questions :
> Are our programmes being created from modules bound by copy are  
> much heavier than if they were bound by copy?

Unclear question! I presume your second reference to 'copy' should  
have been 'reference'. If so, then what do you mean by "heavier"? If  
you mean may occupy more disk space then they MAY do. If the module  
bound by copy is used in only one program there is little advantage  
to putting that module in a service program. If the module is used in  
more than one program then by using a service program you will reduce  
the size of each program and you will simplify maintenance.

> Will this have a noticeable effect on performance?

No. Note that in some cases excessive use of service programs, or  
using a single large service program will have a detrimental  
performance impact.


> I notice we have programmes of 100 MB.

And?

> What happens if a program is called and the procedure in a service  
> program has changed

Depends on how the change was made. If done properly it will have no  
effect on the caller. If done incorrectly then you will have a  
learning experience.

> or if the service program was deleted?

You will get a run-time error when the consuming program is invoked.

> Why bind by copy instead of by reference?

Because it facilitates better code reuse, it provides the ability to  
properly encapsulate function, it gives the ability to define a  
public and private interface, and it gives almost all the benefits of  
dynamic program call without the perceived performance impact.


Regards,
Simon Coulter.
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