Cache not invalidating immediately after file dependency changes

[Andrew Jocelyn]

Hi

I'm running an ASP.NET web application under IIS. I'm inserting a cache
object with a file based CacheDependency. I've noticed that when the file
changes the Cache object is not always immediately invalidated.

e.g. Cache.Insert("myobj", data, new CacheDependency(filePath));

When I make a change to the file 'filePath' and call the object from the
cache it is not null. I'm disposing of the FileStream object immediately
after writing to the file.

e.g. data = Cache["myobj"];

However it appears to be null the second time it is called.

How can I guarantee the object is nulled immediately after the file
dependency has changed?

Thanks
Andrew

[Andrew Jocelyn]

Please find some code and further explanation of my problem:
public class SystemSettingsManager{ private const string _fileName =
"~/scs.config"; public static SystemSettings GetSettings() { HttpContext
context = HttpContext.Current; SystemSettings data =
(SystemSettings)context.Cache["SystemSettings"]; if (data != null)
Debug.WriteLine("Load SystemSettings from cache"); if (data ==
null) { Debug.WriteLine("Load SystemSettings from file");
XmlSerializer serializer = new XmlSerializer(typeof(SystemSettings)); try
{ string filePath = context.Server.MapPath(_fileName); FileStream
fs = new FileStream(filePath, FileMode.Open); data =
(SystemSettings)serializer.Deserialize(fs); fs.Close();
context.Cache.Insert("SystemSettings", data, new
acheDependency(filePath)); } catch (System.IO.FileNotFoundException)
{ data = new SystemSettings(); } } return data; } public
static void SaveSettings(SystemSettings settings) { HttpContext context
= HttpContext.Current; string filePath =
context.Server.MapPath(_fileName); XmlSerializer serializer = new
XmlSerializer(typeof(SystemSettings)); using (FileStream fs = new
FileStream(filePath, FileMode.Create)) { serializer.Serialize(fs,
settings); // added the flush and close to the using block but the problem
remains. fs.Flush(); // Clear all write buffers fs.Close(); // Explicitly
close stream } Debug.WriteLine("Save SystemSettings"); }}I can see
that when I update the FormView (with ObjectDataSource) I get the
following:Load SystemSettings from cacheSave SystemSettingsLoad
SystemSettings from cacheThis happens because the SystemSettings are already
cached somewhere else in the application.When I update the FormView again I
get:Load SystemSettings from fileSave SystemSettingsLoad SystemSettings from
cacheIf I keep doing it I get the same result. In other words it takes a
second call to the GetSettings method before the cache is empty. One other
thing is that when I debug with the Visual Studio web server it always works
as expected. It's only a problem with IIS. I've also tried on 2 different
IIS machines.I'm completely stuck.ThanksAndrew

[Andrew Jocelyn]

Please find some code and further explanation of my problem:

public class SystemSettingsManager
{
private const string _fileName = "~/scs.config";

public static SystemSettings GetSettings()
{
HttpContext context = HttpContext.Current;
SystemSettings data =
(SystemSettings)context.Cache["SystemSettings"];
if (data != null) Debug.WriteLine("Load SystemSettings from cache");
if (data == null)
{
Debug.WriteLine("Load SystemSettings from file");

XmlSerializer serializer = new
XmlSerializer(typeof(SystemSettings));
try
{
string filePath = context.Server.MapPath(_fileName);
FileStream fs = new FileStream(filePath, FileMode.Open);
data = (SystemSettings)serializer.Deserialize(fs);
fs.Close();

context.Cache.Insert("SystemSettings", data, new
acheDependency(filePath));
}
catch (System.IO.FileNotFoundException)
{
data = new SystemSettings();
}
}
return data;
}

public static void SaveSettings(SystemSettings settings)
{
HttpContext context = HttpContext.Current;
string filePath = context.Server.MapPath(_fileName);
XmlSerializer serializer = new
XmlSerializer(typeof(SystemSettings));
using (FileStream fs = new FileStream(filePath, FileMode.Create))
{
serializer.Serialize(fs, settings);
// added the flush and close to the using block but the problem
remains.
fs.Flush(); // Clear all write buffers
fs.Close(); // Explicitly close stream
}
Debug.WriteLine("Save SystemSettings");
}

}

I can see that when I update the FormView (with ObjectDataSource) I get the
following:

Load SystemSettings from cache
Save SystemSettings
Load SystemSettings from cache

This happens because the SystemSettings are already cached somewhere else in
the application. When I update the FormView again I
get:

Load SystemSettings from file
Save SystemSettings
Load SystemSettings from cache

If I keep doing it I get the same result. In other words it takes a
second call to the GetSettings method before the cache is empty. One other
thing is that when I debug with the Visual Studio web server it always works
as expected. It's only a problem with IIS. I've also tried on 2 different
IIS machines.

I'm completely stuck.
Thanks
Andrew

[Allen Chen [MSFT]]

Hi Andrew,

Sorry for the late reply. From your description you see "Load
SystemSettings from cache" even if the file is updated by executing
SaveSettings method, and it only happens when the web site is published,
correct?

I've tested the code you provided. It works fine. My IIS version is 5.1.

What I can guess is, some other code may cause this issue. I think I need
more code to investigate this issue (as you said, you updated the FormView.
What's the code?).

If it still doesn't work please tell me more details about your environment
(operating system, IIS version, Visual Studio version) and send me a demo
project. It will help me reproduce this issue. My email is
v-******@microsoft.com.

Regards,
Allen Chen
Microsoft Online Support

Delighting our customers is our #1 priority. We welcome your comments and
suggestions about how we can improve the support we provide to you. Please
feel free to let my manager know what you think of the level of service
provided. You can send feedback directly to my manager at:
ms****@microsoft.com.

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--------------------
| From: "Andrew Jocelyn" <j0**@newsgroups.nospam>
| References: <eB**************@TK2MSFTNGP03.phx.gbl>
| Subject: Re: Cache not invalidating immediately after file dependency
changes
| Date: Thu, 9 Oct 2008 16:06:36 +0100
| Lines: 81
| X-Priority: 3
| X-MSMail-Priority: Normal
| X-Newsreader: Microsoft Outlook Express 6.00.2900.5512
| X-RFC2646: Format=Flowed; Response
| X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579
| Message-ID: <ux**************@TK2MSFTNGP06.phx.gbl>
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| NNTP-Posting-Host: 88-97-199-158.dsl.zen.co.uk 88.97.199.158
| Path: TK2MSFTNGHUB02.phx.gbl!TK2MSFTNGP01.phx.gbl!TK2MSF TNGP06.phx.gbl
| Xref: TK2MSFTNGHUB02.phx.gbl
microsoft.public.dotnet.framework.aspnet:77602
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| Please find some code and further explanation of my problem:
|
| public class SystemSettingsManager
| {
| private const string _fileName = "~/scs.config";
|
| public static SystemSettings GetSettings()
| {
| HttpContext context = HttpContext.Current;
| SystemSettings data =
| (SystemSettings)context.Cache["SystemSettings"];
| if (data != null) Debug.WriteLine("Load SystemSettings from
cache");
| if (data == null)
| {
| Debug.WriteLine("Load SystemSettings from file");
|
| XmlSerializer serializer = new
| XmlSerializer(typeof(SystemSettings));
| try
| {
| string filePath = context.Server.MapPath(_fileName);
| FileStream fs = new FileStream(filePath, FileMode.Open);
| data = (SystemSettings)serializer.Deserialize(fs);
| fs.Close();
|
| context.Cache.Insert("SystemSettings", data, new
| acheDependency(filePath));
| }
| catch (System.IO.FileNotFoundException)
| {
| data = new SystemSettings();
| }
| }
| return data;
| }
|
| public static void SaveSettings(SystemSettings settings)
| {
| HttpContext context = HttpContext.Current;
| string filePath = context.Server.MapPath(_fileName);
| XmlSerializer serializer = new
| XmlSerializer(typeof(SystemSettings));
| using (FileStream fs = new FileStream(filePath, FileMode.Create))
| {
| serializer.Serialize(fs, settings);
| // added the flush and close to the using block but the
problem
| remains.
| fs.Flush(); // Clear all write buffers
| fs.Close(); // Explicitly close stream
| }
| Debug.WriteLine("Save SystemSettings");
| }
|
| }
|
| I can see that when I update the FormView (with ObjectDataSource) I get
the
| following:
|
| Load SystemSettings from cache
| Save SystemSettings
| Load SystemSettings from cache
|
| This happens because the SystemSettings are already cached somewhere else
in
| the application. When I update the FormView again I
| get:
|
| Load SystemSettings from file
| Save SystemSettings
| Load SystemSettings from cache
|
| If I keep doing it I get the same result. In other words it takes a
| second call to the GetSettings method before the cache is empty. One other
| thing is that when I debug with the Visual Studio web server it always
works
| as expected. It's only a problem with IIS. I've also tried on 2 different
| IIS machines.
|
| I'm completely stuck.
| Thanks
| Andrew
|
|
|

[Andrew Jocelyn]

Hi Allen

I've replied to your email address with a test project.

Thanks
Andrew

[Allen Chen [MSFT]]

Hi Andrew,

Thanks for your project. I've reproduced this issue on my side.

In my opinion, this issue is due to the fact that Cache module need to take
some time to check the dependency and this action is asynchronous to the
execution of the code in your SystemSettings class.Thus, the result is
unpredictable. As you said, some times it works and sometimes not.

After saving the file, if the check finished before the execution of this
line in the GetSettings method it will return null:
data = (SystemSettings)context.Cache["SystemSettings"];

Otherwise, it will return the cached data instead.

To solve this issue we can synchronize ourselves. By adding a flag we can
achieve this effect. Here's the code:

using System.Configuration;
using System.IO;
using System.Web;
using System.Web.Caching;
using System.Xml.Serialization;
using System.Diagnostics;
using System.Threading;
using System;
namespace Empetus.SCS.BLL
{
[System.ComponentModel.DataObject]
public class SystemSettingsManager
{
private const string _fileName = "~/scs.config";
private static bool _readfromfile = false;
private static object _mylock = new object();

[System.ComponentModel.DataObjectMethodAttribute(Sy stem.ComponentModel.DataO
bjectMethodType.Select, true)]
public static SystemSettings GetSettings()
{
HttpContext context = HttpContext.Current;
SystemSettings data;

lock (_mylock)
{
data = (SystemSettings)context.Cache["SystemSettings"];

if (data==null||_readfromfile)
{
context.Response.Write("Load SystemSettings from
file<br/>");

XmlSerializer serializer = new
XmlSerializer(typeof(SystemSettings));
try
{
string filePath = context.Server.MapPath(_fileName);
// create a filestream to read the XML document
FileStream fs = new FileStream(filePath,
FileMode.Open);
// use the Deserialize method to retrieve the oject
state
data = (SystemSettings)serializer.Deserialize(fs);
fs.Flush(); // Clear all write buffers
fs.Close();

context.Cache.Insert("SystemSettings", data, new
CacheDependency(filePath));

}
catch (System.IO.FileNotFoundException)
{
// if the file is not found, return a new empty
class
data = new SystemSettings();
}
}
else
{
context.Response.Write("Load SystemSettings from
cache<br/>");
}
_readfromfile = false;

}

return data;
}
[System.ComponentModel.DataObjectMethodAttribute(Sy stem.ComponentModel.DataO
bjectMethodType.Update, true)]
public static void SaveSettings(SystemSettings settings)
{
lock (_mylock)
{
HttpContext context = HttpContext.Current;
string filePath = context.Server.MapPath(_fileName);
XmlSerializer serializer = new
XmlSerializer(typeof(SystemSettings));

using (FileStream fs = new FileStream(filePath,
FileMode.Create))
{
serializer.Serialize(fs, settings);
fs.Flush(); // Clear all write buffers
fs.Close(); // Explicitly close stream
context.Cache.Insert("SystemSettings", settings, new
CacheDependency(filePath));
}
_readfromfile = true;
}
Debug.WriteLine("Save SystemSettings");
}
}
}
If a user saves the settings we can get notified via the _readfromfile
flag. It tells us to read from the file instead of the cache. Then in the
GetSettings method we can check the flag and read the data from the
appropriate place.
Please have a try and let me know if it works.

Regards,
Allen Chen
Microsoft Online Support

--------------------
| From: "Andrew Jocelyn" <j0**@newsgroups.nospam>
| References: <eB**************@TK2MSFTNGP03.phx.gbl>
<ux**************@TK2MSFTNGP06.phx.gbl>
<Bl**************@TK2MSFTNGHUB02.phx.gbl>
| Subject: Re: Cache not invalidating immediately after file dependency
changes
| Date: Tue, 14 Oct 2008 13:11:54 +0100
| Lines: 8
| X-Priority: 3
| X-MSMail-Priority: Normal
| X-Newsreader: Microsoft Outlook Express 6.00.2900.5512
| X-RFC2646: Format=Flowed; Original
| X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579
| Message-ID: <ea**************@TK2MSFTNGP05.phx.gbl>
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| NNTP-Posting-Host: 88-97-199-158.dsl.zen.co.uk 88.97.199.158
| Path: TK2MSFTNGHUB02.phx.gbl!TK2MSFTNGP01.phx.gbl!TK2MSF TNGP05.phx.gbl
| Xref: TK2MSFTNGHUB02.phx.gbl
microsoft.public.dotnet.framework.aspnet:77846
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| Hi Allen
|
| I've replied to your email address with a test project.
|
| Thanks
| Andrew
|
|
|

[Andrew Jocelyn]

Hi Allen

I think your analysis makes sense. I'm working on another project at the
moment so I won't be able to test your code for a couple of weeks. I'll
update you as soon as I have.

Thanks
Andrew

[Allen Chen [MSFT]]

Hi Andrew,

Do you have any progress on this issue?

Regards,
Allen Chen
Microsoft Online Support
--------------------
| From: "Andrew Jocelyn" <j0**@newsgroups.nospam>
| References: <eB**************@TK2MSFTNGP03.phx.gbl>
<ux**************@TK2MSFTNGP06.phx.gbl>
<Bl**************@TK2MSFTNGHUB02.phx.gbl>
<ea**************@TK2MSFTNGP05.phx.gbl>
<Wr**************@TK2MSFTNGHUB02.phx.gbl>
| Subject: Re: Cache not invalidating immediately after file dependency
changes
| Date: Thu, 16 Oct 2008 10:18:30 +0100
| Lines: 10
| X-Priority: 3
| X-MSMail-Priority: Normal
| X-Newsreader: Microsoft Outlook Express 6.00.2900.5512
| X-RFC2646: Format=Flowed; Original
| X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579
| Message-ID: <#j**************@TK2MSFTNGP02.phx.gbl>
| Newsgroups: microsoft.public.dotnet.framework.aspnet
| NNTP-Posting-Host: 88-97-199-158.dsl.zen.co.uk 88.97.199.158
| Path: TK2MSFTNGHUB02.phx.gbl!TK2MSFTNGP01.phx.gbl!TK2MSF TNGP02.phx.gbl
| Xref: TK2MSFTNGHUB02.phx.gbl
microsoft.public.dotnet.framework.aspnet:77977
| X-Tomcat-NG: microsoft.public.dotnet.framework.aspnet
|
| Hi Allen
|
| I think your analysis makes sense. I'm working on another project at the
| moment so I won't be able to test your code for a couple of weeks. I'll
| update you as soon as I have.
|
| Thanks
| Andrew
|
|
|