Remoting Lifetime Leases

[Mikael]

Has anyone seen some examples of how to handle lifetime of client activated
remoting objects?

The lifetime sponsorship mechanism described in the .NET documentation is
a way to complicated to understand without examples. Unfortunally I have
not found any examples.

One way to handle liftime is to periodically call a ReNewLifeTime() method
on the remoting object, but I Am sure there are more clean ways to do this.

// Mikael

[Tom Barnaby]

"Mikael" <mjs@nospam.beamex.fi> wrote:
>
>
>Has anyone seen some examples of how to handle lifetime of client activated
>remoting objects?
>

Yep, in my courseware and in the Remoting chapter of the book I'm writing
;-)

>The lifetime sponsorship mechanism described in the .NET documentation is
>a way to complicated to understand without examples.

Not to mention the fact that the .NET doc gives the wrong XML element names
when describing how to configure the lifetimes. :-(

Anyhow, there is a lot to cover in this, since there a 2 or 3 ways to accomplish
the same thing. But here is an example using the remoting config file to
set up the lease settings:

<configuration>
<system.runtime.remoting>
<application name="Server">

<!-- Configure default lease settings -->
<lifetime leaseTime="5s" renewOnCallTime="5s"
sponsorshipTimeout="5s" leaseManagerPollTime = "5s" />

<!-- Configure client activated objects -->
<service>
<activated type="MathLibrary.HelloWorld, MathLibrary" />
</service>

<!-- Configure channels etc ... -->
</application>
</system.runtime.remoting>
</configuration>

The meanings of the <lifetime> attributes are as follows:

leaseTime = The initial lease time period

renewOnCallTime = How much lease time to give on each method call

sponsorshipTimeOut = How long to wait for a sponser to give more lease time
to an object about to be orphaned.

leaseManagerPollTime = How often the runtime checks the leases of client
activated objects.


You can also let each remoted class determine its lease by overriding the
MarshalByRefObject.InitializeLifeTimeService method:

Public Class CAOHelloWorld
Inherits MarshalByRefObject

Overrides Function InitializeLifeTimeService() As Object
Dim oLease As ILease

oLease = CType(MyBase.InitializeLifetimeService(), ILease)
If oLease.CurrentState = LeaseState.Initial Then
oLease.InitialLeaseTime = TimeSpan.FromSeconds(2)
oLease.SponsorshipTimeout = TimeSpan.FromSeconds(2)
oLease.RenewOnCallTime = TimeSpan.FromSeconds(2)
End If
Return oLease
End Function
End Class


Leases are renewed in 2 ways:

1) Whenever a client invokes a method on a client activated object, the runtime
renews the lease to the renewOnCallTime value.

2) When an object's lease expires, the runtime searches for sponsor objects
(objects that implement the ISponsor interface). The runtime gives each the
opportunity to renew the lease by invoking the sponsor's Renewal method.

The following code shows a sponser object that will renew a lease exactly
3 times.

Public Class HelloSponsor
Implements ISponsor
Inherits MarshalByRefObject

Private mRenewCount As Integer

Public Function Renewal(ByVal theLease As ILease) _
As TimeSpan Implements ISponsor.Renewal
If mRenewCount < 3 Then
mRenewCount += 1
Return TimeSpan.FromSeconds(5)
Else
Return TimeSpan.FromSeconds(0)
End If
End Function
End Class

Here is the code to register this sponser object with a remoted object called
oHello. Note that the GetLifeTimeService method is used to retrieve the lease
info for the object. This method is inheritted from MarshalByRefObject.

'Register a sponsor
Dim oLease As ILease

'Get the remote object’s lease.
oLease = CType(oHello.GetLifetimeService(), ILease)
oLease.Register(New HelloSponsor())

HTH
Tom Barnaby
www.intertech-inc.com

[Mikael]

"Tom Barnaby" <tbarnaby@intertech-inc.cm> wrote:
>
>Yep, in my courseware and in the Remoting chapter of the book I'm writing
>;-)

When and where will your book be released and what is it's name?

>Leases are renewed in 2 ways:

Thank you for your excellent answer. I have however one more question, just
to verify i got it right!

<snip..>

>2) When an object's lease expires, the runtime searches for sponsor
> objects (objects that implement the ISponsor interface). The runtime
> gives each the opportunity to renew the lease by invoking the sponsor's

> Renewal method.
>
>The following code shows a sponser object that will renew a lease.
>
>Public Class HelloSponsor
> Implements ISponsor
> Inherits MarshalByRefObject

Can this class (implementing ISponsor) be located on the client side, while
the object whose lifetime need to be renewed is on server side?

The Renewal function could then look like this:

Public Function Renewal(ByVal theLease As ILease) _
As TimeSpan Implements ISponsor.Renewal

If Not Me.Disposed Then
Return TimeSpan.FromSeconds(5)
Else
Return TimeSpan.FromSeconds(0)
End If

End Function

Is it even possible (or decent design) to crossreference assemblies like
this?

Any thoughts?

[Tom Barnaby]

"Mikael" <mjs@nospam.beamex.fi> wrote:
>
>"Tom Barnaby" <tbarnaby@intertech-inc.cm> wrote:
>>
>>Yep, in my courseware and in the Remoting chapter of the book I'm writing
>>;-)
>
>When and where will your book be released and what is it's name?
>

It is "Distributed .NET" from A-press. Scheduled publish date is at the end
of the year, but could be later if I don't stop reading these news boards.
;-)

>
>Thank you for your excellent answer. I have however one more question, >just
to verify i got it right!

>Can this class (implementing ISponsor) be located on the client side, >while
the object whose lifetime need to be renewed is on server side?
>

Yep, in fact, the example I gave is actually from a client side sponsor.
The sponsor registration code I posted also executes on the client.

>Is it even possible (or decent design) to crossreference assemblies like
>this?
>
>Any thoughts?
>

Its not something I would do consistently. The reason .NET implements lease
based lifetimes as opposed to the current DCOM ref counting scheme is to
remove the need for the server to periodically ping clients to ensure they
are still alive. This advantage is removed if you implement client side sponsors.


On the other hand, sometimes you may have client side logic that determines
whether the remote object can be destroyed. You really have no other choice
in this case.

Tom Barnaby
www.intertech-inc.com