Avoiding redundant storage. Share keyword?

  • Thread starter Thread starter Gregory Gadow
  • Start date Start date
G

Gregory Gadow

In a VB.Net 2.0 project, I have a WizardClass that contains a List (of
RuleClass). Each rule needs access to variables within it's parent
wizard, so the constructor for RuleClass is New (ByVal Wizard as
WizardClass). Each rule then has a property Private Wiz as WizardClass,
which is set in Sub New with Wiz = Wizard. Currently there is only one
Wizard in the project but there might be more in the future to handle
different rulesets.

My understanding is that, with this, each instance of RuleClass has its
own isolated and independent copy of WizardClass, which would take up a
huge amount of memory if there are a lot of rules. This is part of a
service, so the memory would be permanently used. Is this actually the
case? If so, any suggestions on how to prevent this memory use?

I am thinking that I can declare each instance of WizardClass to be
Shared, so in the service module:

Private Shared Wizzie1 as WizardClass
Private Shared Wizzie2 as WizardClass

would create independent instances of WizardClass and each time Wizzie1
or Wizzie2 appear on the right of an = a pointer to the instance would
be generated rather than a copy. So in the LoadRuleset method of
WizardClass

mRulesList.Add(New RuleClass(Me))

would create only a pointer to the shared parent wizard rather than a
complete copy of the wizard object. Will this do what I think it will?
Will this happen automatically when the project is compiled and
(hopefully) optimized? Or am I barking up the wrong tree entirely?

Thanks in advance for any help.
--
Gregory Gadow
(e-mail address removed)
http://www.serv.net/~techbear

"[W]e have never held that moral disapproval, without any other asserted

state interest, is a sufficient rationale under the Equal Protection
Clause to justify a law that discriminates among groups of persons."
- Sandra Day O`Conner, _Lawrence v Texas_
http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vol=000&invol=02-102
 
Gregory Gadow said:
In a VB.Net 2.0 project, I have a WizardClass that contains a List (of
RuleClass). Each rule needs access to variables within it's parent
wizard, so the constructor for RuleClass is New (ByVal Wizard as
WizardClass). Each rule then has a property Private Wiz as WizardClass,
which is set in Sub New with Wiz = Wizard. Currently there is only one
Wizard in the project but there might be more in the future to handle
different rulesets.

My understanding is that, with this, each instance of RuleClass has its
own isolated and independent copy of WizardClass
Click to expand...

If you are passing the reference to an existing 'WizardClass' object to the
new object and store the reference to this object there, only an additional
reference is created. Both instances will reference the same 'WizardClass'
object afterwards.
, which would take up a
huge amount of memory if there are a lot of rules. This is part of a
service, so the memory would be permanently used. Is this actually the
case? If so, any suggestions on how to prevent this memory use?
Click to expand...

No, it isn't the case if 'WizardClass' is a reference type, e.g. a class.
I am thinking that I can declare each instance of WizardClass to be
Shared, so in the service module:

Private Shared Wizzie1 as WizardClass
Private Shared Wizzie2 as WizardClass

would create independent instances of WizardClass
Click to expand...

The code above doesn't create instance of /classes/ at all. It only
declares variables which reference 'Nothing' by default. If you assign the
same reference to both variables later, only a single instance of
'WizardClass' exists.
 
Herfried K. Wagner said:
If you are passing the reference to an existing 'WizardClass' object to the
new object and store the reference to this object there, only an additional
reference is created. Both instances will reference the same 'WizardClass'
object afterwards.
Click to expand...

I can make the whole issue go away by using ByRef in the constructor of
RuleClass?

In that case, this code in RuleClass will store only a reference and not a
complete instance

Private Wiz as WizardClass

Public Sub New(ByRef MyWizard as WizardClass)
Wiz = MyWizard
....
End Sub

and latter calls of

Wiz.DefaultPrinter

will all reference the same block of memory?

/slaps forehead

Some things in .NET are too bloody obvious to be seen. Thanks.
No, it isn't the case if 'WizardClass' is a reference type, e.g. a class.


The code above doesn't create instance of /classes/ at all. It only
declares variables which reference 'Nothing' by default. If you assign the
same reference to both variables later, only a single instance of
'WizardClass' exists.
Click to expand...

Correct, I should have written

Private Shared Wizzie1 as New WizardClass(<various parameters>)
Private Shared Wizzie2 as New WizardClass(<different parameters>)

Not that it matters now.
--
Gregory Gadow
(e-mail address removed)
http://www.serv.net/~techbear

"[W]e have never held that moral disapproval, without any other asserted
state interest, is a sufficient rationale under the Equal Protection
Clause to justify a law that discriminates among groups of persons."
- Sandra Day O`Conner, _Lawrence v Texas_
http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vol=000&invol=02-102
 
Gregory Gadow said:
I can make the whole issue go away by using ByRef in the constructor of
RuleClass?
Click to expand...

No, you do not need a 'ByRef' here as 'WizardClass' is already a reference
type. Even with 'ByRef', which I recommend in this sitation, no copy of the
'WizardClass' /object/ is created.
In that case, this code in RuleClass will store only a reference and not a
complete instance

Private Wiz as WizardClass

Public Sub New(ByRef MyWizard as WizardClass)
Wiz = MyWizard
...
End Sub
Click to expand...

Even with 'ByVal' instead of 'ByRef' it will only store a reference.
and latter calls of

Wiz.DefaultPrinter

will all reference the same block of memory?
Click to expand...

Yes, they reference the same object (class instance).
 
Herfried K. Wagner said:
No, you do not need a 'ByRef' here as 'WizardClass' is already a reference
type. Even with 'ByRef', which I recommend in this sitation, no copy of the
'WizardClass' /object/ is created.
Click to expand...

Did you mean "Event with 'ByVal', which I recommend [...]"? That's what
I'd expect :)

Gregory: See http://www.pobox.com/~skeet/csharp/parameters.html for
details of parameter passing. It's C#-based, but the basics are the
same for VB.NET. (There are a few differences, such as properties not
being able to be passed by reference in C#, but it should still be
useful in terms of concepts.)
 
Jon,

Jon Skeet said:
No, you do not need a 'ByRef' here as 'WizardClass' is already a
reference
type. Even with 'ByRef', which I recommend in this sitation, no copy of
the
'WizardClass' /object/ is created.
Click to expand...

Did you mean "Event with 'ByVal', which I recommend [...]"? That's what
I'd expect :)
Click to expand...

Yep. I wanted to type 'ByVal'. Thanks for pointing out this "bug" in my
post.
 
Jon Skeet said:
Herfried K. Wagner said:
No, you do not need a 'ByRef' here as 'WizardClass' is already a reference
type. Even with 'ByRef', which I recommend in this sitation, no copy of the
'WizardClass' /object/ is created.
Click to expand...

Did you mean "Event with 'ByVal', which I recommend [...]"? That's what
I'd expect :)

Gregory: See http://www.pobox.com/~skeet/csharp/parameters.html for
details of parameter passing. It's C#-based, but the basics are the
same for VB.NET. (There are a few differences, such as properties not
being able to be passed by reference in C#, but it should still be
useful in terms of concepts.)
Click to expand...

I'm familiar enough with C and C++ that the basics of C# are no problem. Thanks,
the page is a nice resource.
 
Back
Top