Re: [EXT] Re: Advice passing a large parameter -- RPG400-L

I agree with David’s assessment. By default, RPG passes parameters by reference, meaning that a pointer is passed from the caller’s scope, so that the called program can access the callers storage directly.

The size and format of the address space is agreed upon by both parties. Since no data is actually being moved, the size of the parameter data is irrelevant to the performance question.

Passing by value is the expensive option you should try to avoid. This also includes large “return values” which are also passed by value. IBM gave us RTNPARM option to resolve that issue, but it’s not the default behavior, so just be aware.

Passing with CONST option performs well despite some small overhead with initialization of constant value storage in caller.

-Eric DeLong

On Apr 12, 2019, at 9:18 AM, David Gibbs via RPG400-L <rpg400-l@xxxxxxxxxxxxxxxxxx> wrote:

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On 4/12/2019 9:11 AM, Greg Wilburn wrote:
1. Just define the DS the same and pass it in (it could be
CONST)

I'm pretty sure this is the best way to do it. If you define the parm as const, I'm pretty sure it will be passed by reference, so there will be no additional storage allocated.

3. Define the PI as pointer and pass the address

No need to do this, as mentioned above, that's essentially what's already happening.

david

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