Static Variable Reference in Web Service?

[depalau]

I'm running into some issues on maintaining a static variable across
the lifetime of a web service and I was wondering if anyone could help.

Background:

We have developed a C#/1.1 web service running on IIS 5/6 that
interfaces with a 3rd party DLL referenced by using the DLLImport
attribute.

Interacting with this 3rd party software through this dll requires an
initialization call to it which prepares it for subsequent functional
calls. Once all of our functional calls are made, we need to call
another dll function to close it's resources (it is a license based
application).

Due to the amount of resources needed by this 3rd party software and
the amount of web service calls made against it, it is recommened that
we only initialize it once and 'close' it only when our web service
gets recycled by IIS after a period of inactivity. Initializing this
dll returns a number that we use to perform any functionality call and
to close the software (serverID).

I have placed the call to initialize in the global.asax
Application_Start method and the call to close in the Application_End
method.

Our code looks a little like:

public class 3rdParty
{

public static short serverID;

public static void Initialize()
{
Close();
serverID = OpenServer();
}

public static void Close()
{
if (serverID > 0)
{
CloseServer(serverID);
}
}

[DllImport("3rdParty2.DLL", EntryPoint ="OpenServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern short OpenServer();

[DllImport("PCMSRV32.DLL", EntryPoint = "CloseServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern int CloseServer(short serverID);
}


In the global.asax file:

protected void Application_Start(Object sender, EventArgs e)
{
3rdParty.Initialize();
}

protected void Application_End(Object sender, EventArgs e)
{
3rdParty.Close();
}


What is happening is that if we have a lull in access to the web
service, IIS will recycle the app domain. The next time the web
service gets started up, it will attempt to call OpenServer() again,
but since CloseServer() was never called, this 3rd party software won't
accept another OpenServer call until it is closed with the previous
serverID.

Am I going about this the right way by having a static serverID
variable? Should I be storing this value somewhere else for access?

Any input would be greatly appreciated.

Thanks,

-David

 

[bruce barker \(sqlwork.com\)]

the dll is actually loaded by the aspnet worker process that hosts the
appdomain. a normal recycle load a new appdomain, then unloads the old
domain. when this happen the second load will be called before the first
unload.

you should write another c/c++ dll that manages the open and close (it can
use a static).

-- bruce (sqlwork.com)

I'm running into some issues on maintaining a static variable across
the lifetime of a web service and I was wondering if anyone could help.

Background:

We have developed a C#/1.1 web service running on IIS 5/6 that
interfaces with a 3rd party DLL referenced by using the DLLImport
attribute.

Interacting with this 3rd party software through this dll requires an
initialization call to it which prepares it for subsequent functional
calls. Once all of our functional calls are made, we need to call
another dll function to close it's resources (it is a license based
application).

Due to the amount of resources needed by this 3rd party software and
the amount of web service calls made against it, it is recommened that
we only initialize it once and 'close' it only when our web service
gets recycled by IIS after a period of inactivity. Initializing this
dll returns a number that we use to perform any functionality call and
to close the software (serverID).

I have placed the call to initialize in the global.asax
Application_Start method and the call to close in the Application_End
method.

Our code looks a little like:

public class 3rdParty
{

public static short serverID;

public static void Initialize()
{
Close();
serverID = OpenServer();
}

public static void Close()
{
if (serverID > 0)
{
CloseServer(serverID);
}
}

[DllImport("3rdParty2.DLL", EntryPoint ="OpenServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern short OpenServer();

[DllImport("PCMSRV32.DLL", EntryPoint = "CloseServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern int CloseServer(short serverID);
}


In the global.asax file:

protected void Application_Start(Object sender, EventArgs e)
{
3rdParty.Initialize();
}

protected void Application_End(Object sender, EventArgs e)
{
3rdParty.Close();
}


What is happening is that if we have a lull in access to the web
service, IIS will recycle the app domain. The next time the web
service gets started up, it will attempt to call OpenServer() again,
but since CloseServer() was never called, this 3rd party software won't
accept another OpenServer call until it is closed with the previous
serverID.

Am I going about this the right way by having a static serverID
variable? Should I be storing this value somewhere else for access?

Any input would be greatly appreciated.

Thanks,

-David

 

[depalau]

Thanks for responding.

I'm a little confused, with this new DLL you mention, who would host
that? Wouldn't it still be the aspnet worker process?

I should have been a little clearer in my description of how our
project is set up:

We have an assembly (MyCompany.MyApp.WebService) that contains the web
service that points to another assembly (MyCompany.MyApp.Library) that
contains the 3rdParty class that holds the static variable and static
DLLImport references to the 3rd party supplied dll (3rdParty.dll).

How would adding another C/C++ dll that contains the 3rd party
interfaces still be around if the reference to it from the web service
assembly goes away? And why C/C++?

Sorry if I'm misunderstanding certain things, I don't have much
experience in maintaining information in web service apps that need to
stick around like this.

 

[John Saunders]

I'm running into some issues on maintaining a static variable across
the lifetime of a web service and I was wondering if anyone could help.

Background:

We have developed a C#/1.1 web service running on IIS 5/6 that
interfaces with a 3rd party DLL referenced by using the DLLImport
attribute.

Interacting with this 3rd party software through this dll requires an
initialization call to it which prepares it for subsequent functional
calls. Once all of our functional calls are made, we need to call
another dll function to close it's resources (it is a license based
application).

Due to the amount of resources needed by this 3rd party software and
the amount of web service calls made against it, it is recommened that
we only initialize it once and 'close' it only when our web service
gets recycled by IIS after a period of inactivity. Initializing this
dll returns a number that we use to perform any functionality call and
to close the software (serverID).

I have placed the call to initialize in the global.asax
Application_Start method and the call to close in the Application_End
method.

Our code looks a little like:

public class 3rdParty
{

public static short serverID;

public static void Initialize()
{
Close();
serverID = OpenServer();
}

public static void Close()
{
if (serverID > 0)
{
CloseServer(serverID);
}
}

[DllImport("3rdParty2.DLL", EntryPoint ="OpenServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern short OpenServer();

[DllImport("PCMSRV32.DLL", EntryPoint = "CloseServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern int CloseServer(short serverID);
}


In the global.asax file:

protected void Application_Start(Object sender, EventArgs e)
{
3rdParty.Initialize();
}

protected void Application_End(Object sender, EventArgs e)
{
3rdParty.Close();
}


What is happening is that if we have a lull in access to the web
service, IIS will recycle the app domain. The next time the web
service gets started up, it will attempt to call OpenServer() again,
but since CloseServer() was never called, this 3rd party software won't
accept another OpenServer call until it is closed with the previous
serverID.

Am I going about this the right way by having a static serverID
variable? Should I be storing this value somewhere else for access?

Any input would be greatly appreciated.

First of all, you said that CloseServer is never called. Remove the
conditional in Close() and see what happens. If it's still not getting
called, it may be because Application_End is not being called.

Statics only last as long as the AppDomain does. When IIS recycles your
AppDomain, any statics go away with it. I wonder how the third-party DLL
manages not to be cleaned up when the AppDomain is terminated. Is any part
of it a COM+ application or an application which runs in a separate process?

BTW, it probably isn't a problem for you right now, but be aware that all
threads in your web service can access the same static variable. If it's
something that's being changed, then you need to use locks to serialize
access to it. Otherwise you can have multiple requests all operating on the
static at the same time.


John

 

[David Palau]

I just noticed that I mis-typed our code in the DLLImport declarations,
sorry. Here is what it is for clarity.

Our code looks a little like:

public class 3rdParty
{

public static short serverID;

public static void Initialize()
{
Close();
serverID = OpenServer();
}

public static void Close()
{
if (serverID > 0)
{
CloseServer(serverID);
}
}

[DllImport("3rdParty.DLL", EntryPoint ="OpenServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern short OpenServer();

[DllImport("3rdParty.DLL", EntryPoint = "CloseServer",
ExactSpelling = false, CharSet = CharSet.Ansi, SetLastError = true)]
private static extern int CloseServer(short serverID);
}


In the global.asax file:

protected void Application_Start(Object sender, EventArgs e)
{
3rdParty.Initialize();
}

protected void Application_End(Object sender, EventArgs e)
{
3rdParty.Close();
}

First of all, you said that CloseServer is never called. Remove the
conditional in Close() and see what happens. If it's still not getting
called, it may be because Application_End is not being called.

Correct, I am not seeing the Close() call ever fire (unless I manually
change the global.asax file or call IISRest or something like that
which triggers this). I don't see it fire as part of the recycle
process. I don't think the conditional will matter since a successful
call to OpenServer will return a short larger than 0.

Statics only last as long as the AppDomain does. When IIS recycles your
AppDomain, any statics go away with it. I wonder how the third-party DLL
manages not to be cleaned up when the AppDomain is terminated. Is any part
of it a COM+ application or an application which runs in a separate process?

I don't think the third-party DLL cleans up any open connections when
it goes out of scope, they made it very clear that in order to free up
licenses, you have to call CloseServer().

BTW, it probably isn't a problem for you right now, but be aware that all
threads in your web service can access the same static variable. If it's
something that's being changed, then you need to use locks to serialize
access to it. Otherwise you can have multiple requests all operating on the
static at the same time.

For this application it is fine, in fact desirable, that we use the
same serverID. What you say makes sense concerning the AppDomain going
away blowing away all of the static variables. Do you have any
suggestions on how to persist this data past that event? Write it to
some file? Use some sort of session state? Thanks for the reply.

 

[John Saunders]

Correct, I am not seeing the Close() call ever fire (unless I manually
change the global.asax file or call IISRest or something like that
which triggers this). I don't see it fire as part of the recycle
process. I don't think the conditional will matter since a successful
call to OpenServer will return a short larger than 0.

The reason I suggested removing the conditional is that it's an easy way to
be sure.

I don't think the third-party DLL cleans up any open connections when
it goes out of scope, they made it very clear that in order to free up
licenses, you have to call CloseServer().

If it's open resources which are the problem, then perhaps your web service
needs to have a higher isolation level in IIS. Maybe it should run in its
own process. It really sounds like the kind of thing that shouldn't be
running in-process in a production service.

For this application it is fine, in fact desirable, that we use the
same serverID. What you say makes sense concerning the AppDomain going
away blowing away all of the static variables. Do you have any
suggestions on how to persist this data past that event? Write it to
some file? Use some sort of session state? Thanks for the reply.

You really need to get this old DLL running in it's own process. It sounds
like the sort of thing that expects process deletion to clean up its messes.

John

 

[Guest]

Hi,
I faced a similar issue earlier this month where we were accessing a COM DLL
from our web service. Every time a new (2nd instance) of the COM object was
created, the web service 'froze'. Thus, not letting the web service create a
2nd instance of the COM object.
I read this article on MSDN, implemented it, and solved the issue.
Take a look at it, this might resolve the issue you are facing:

Running ASMX Web Services on STA Threads
http://msdn.microsoft.com/msdnmag/issues/06/10/WickedCode/

regards,
Rajat Kaushish
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