Samurai Programmer.com - .NET

Micro optimization or just good coding practice?

Greg Varveris — Sat, 21 Aug 2010 04:36:27 GMT

This is a common topic and I thought I’d write up some thoughts I have on it. In-fact, I was just working with a customer on improving their code reviews and what they should be checking for and the question arose - “Should performance be targeted during a code review?” It’s an interesting question. I’m a big fan of performance testing early and often and not waiting until the end of a dev cycle but code reviews, IMO, should focus on logic, maintainability and best practices. I may be in the minority and if you look around the web, you’ll see varying opinions on the topic. For example, one of the PAG articles states:

“Code reviews should be a regular part of your development process. Performance and scalability code reviews focus on identifying coding techniques and design choices that could lead to performance and scalability issues. The review goal is to identify potential performance and scalability issues before the code is deployed. The cost and effort of fixing performance and scalability flaws at development time is far less than fixing them later in the product deployment cycle.

Avoid performance code reviews too early in the coding phase because this can restrict your design options. Also, bear in mind that that performance decisions often involve tradeoffs. For example, it is easy to reduce maintainability and flexibility while striving to optimize code.”

As I mentioned above, I am a huge proponent of performance analysis and optimization many times throughout a typical product development cycle. I can say with a fair amount of certainty that if you don’t build performance reviews into your project plan at regular intervals, you will hit some problem (or multiple problems) in production and have to refactor some code.

Circling back to the original question, though, are code reviews the place for performance analysis? Typically, I’d recommend using them to squash little bits of bad code but maintainability and code-cleanliness should be first and foremost in your minds. That said, if you see a pattern that you know can be improved, by all means bring it up. What’s an example of that type of situation?

Let’s take a look at predicates, specifically their usage in the Find method of a List<T>. If you’re not aware, the Find() method performs a linear search through all of the items until it finds the first match – then it returns. This makes it a O(n) operation where “n” is the number of items in the list. Basically, this means that the more items you have in the list, the longer a Find() operation can potentially take. So, if we slam about 10,000 elements into a list:

private static List<Data>
LoadList()

{

List<Data> myList = new List<Data>();

for (int i
= 0; i < 10000; i++)

{

myList.Add(new Data() { Id = "Id" +
i.ToString(), 


Value = "Value" + i.ToString() });

}



return myList;

}

Then, if someone wants to return the instance of the Data class that contains an Id of say “Id10000”, they might write the following code:

static Data
Find1(List<Data> myList, string idToFind)

{

Data data = myList.Find(s => 


s.Id.ToLower() == 


idToFind.ToLower());



return data;

}

Now, keep in mind that the predicate is executed for each element in the List<T> until it finds the instance you care about. With that in mind, we would probably want to refactor out the “idToFind.ToLower()” above the predicate since that value isn’t changing. So, you might end-up with something like this:

static Data
Find2(List<Data> myList, string idToFind)

{



idToFind = idToFind.ToLower();



Data data = myList.Find(s => 


s.Id.ToLower() == 


idToFind);



return data;

}

Another route you may want to go is just to use the string.Equals(…) method to perform the comparison. That would look like:

static Data
Find3(List<Data> myList, string idToFind)

{



Data data = myList.Find(s => 


string.Equals(

s.Id, 


idToFind, 


StringComparison.

InvariantCultureIgnoreCase)

);



return data;



}

Fact is, the last method IS the fastest way to perform the operation. I can say that without even needing to run it through a profiler. But if you don’t believe me…

Function Name	Elapsed Inclusive Time
...Find1(System.Collections.Generic.List`1<....Data>,string)	6.34
...Find2(System.Collections.Generic.List`1<....Data>,string)	4.47
...Find3(System.Collections.Generic.List`1<....Data>,string)	3.65

That’s something I might put into the category of a micro-optimization AND just good coding practice. But is this something that should be caught during a code review? I’d say “yes” because logically it all makes sense and none of the solutions would really hurt maintainability or readability of the code.

So, I’d tag this as a good coding practice. Other thoughts on the topic?

Enjoy!

Azure: Why did my role crash?

Greg Varveris — Tue, 03 Aug 2010 06:48:17 GMT

One thing you might encounter when you start your development on Windows Azure> is that there is an insane number of options available for number of options for logging. You can view a quick primer here. One of the things that I like about it is that you don’t necessarily need to learn a whole new API just to use it. Instead, the logging facilities in Azure integrates really well with the existing Debug and Trace Logging API in .NET. This is a really nice feature and is done very well in Azure. In-fact to set-up and configure it is all of about 5 lines of code. Actually it’s four lines of code with one line that wraps:

 1: public override bool OnStart() 

 2: { 

 3: DiagnosticMonitorConfiguration
dmc = 

 4: DiagnosticMonitor.GetDefaultInitialConfiguration(); 

 5: dmc.Logs.ScheduledTransferPeriod
= TimeSpan.FromMinutes(1); 

 6: dmc.Logs.ScheduledTransferLogLevelFilter
= LogLevel.Verbose;

 7: DiagnosticMonitor.Start("DiagnosticsConnectionString",
dmc); 

 8: } 

One specific item to note is the ScheduledTransferPeriod property of the Logs property. The minimum value you can set for that property is the equivalent of 1 minute. The only downside to this method of logging is that if your Azure role crashes within that minute, whatever data you have written to your in-built logging will be lost. This also means that if you are writing exceptions to your logging, that will be lost as well. That can cause problems if you’d like to know both when your role crashed and why (the exception details).

Before we talk about a way to get around it, let’s review why the Role might crash. In the Windows Azure world, there are two primary roles that you will use, a Worker and Web role. Main characteristics and reasons it would crash are below:

Role Type	Analogous	Why would it crash/restart?
Worker Role	Console Application	Any unhandled exception.
Web Role	ASP.NET Application hosted in IIS 7.0+	Any unhandled exception thrown on a background thread. StackOverflowException Unhandled exception on finalizer thread.

As you can see, the majority of the reasons why an Azure role would recycle/crash/restart are essentially the same as with any other application – essentially an unhandled exception. Therefore, to mitigate this issue, we can subscribe to the AppDomain’s UnhandledException Event. This event is fired when your application experiences an exception that is not caught and will fire RIGHT BEFORE the application crashes. You can subscribe to this event in the Role OnStart() method:

public override bool OnStart()

{

AppDomain
appDomain = AppDomain.CurrentDomain;

appDomain.UnhandledException
+= 

new UnhandledExceptionEventHandler(appDomain_UnhandledException);

...

}

You will now be notified right before your process crashes. The last piece to this puzzle is logging the exception details. Since you must log the details right when it happens, you can’t just use the normal Trace or Debug statements. Instead, we will write to the Azure storage directly. Steve Marx has a good blog entry about printf in the cloud. While it works, it requires the connection string to be placed right into the logging call. He mentions that you don’t want that in a production application. in our case, we will do things a little bit differently. First, we must add the requisite variables and initialize the storage objects:

private static bool storageInitialized
= false;

private static object gate
= new Object();

private static CloudBlobClient
blobStorage;

private static CloudQueueClient
queueStorage;

  

private void InitializeStorage()

{

if (storageInitialized)

{

return;

}

  

lock (gate)

{

if (storageInitialized)

{

return;

}

  

  

//
read account configuration settings

var
storageAccount = 

CloudStorageAccount.FromConfigurationSetting("DataConnectionString");

  

//
create blob container for images

blobStorage
= 

storageAccount.CreateCloudBlobClient();

CloudBlobContainer
container = blobStorage.

GetContainerReference("webroleerrors");

  

container.CreateIfNotExist();

  

//
configure container for public access

var
permissions = container.GetPermissions();

permissions.PublicAccess
= 

BlobContainerPublicAccessType.Container;

container.SetPermissions(permissions);

  

storageInitialized
= true;

}

}

This will instantiate the requisite logging variables and then when the InitializeStorage() method is executed, we will set these variables to the appropriate initialized values. Lastly, we must call this new method and then write to the storage. We put this code in our UnhandledException event handler:

void appDomain_UnhandledException(object sender,
UnhandledExceptionEventArgs e)

{

//
Initialize the storage variables.

InitializeStorage();

  

//
Get Reference to error container.

var
container = blobStorage.

GetContainerReference("webroleerrors");

  

  

if (container
!= null)

{

//
Retrieve last exception.

Exception
ex = e.ExceptionObject as Exception;

  

if (ex
!= null)

{

//
Will create a new entry in the container

//
and upload the text representing the 

//
exception.

container.GetBlobReference(

String.Format(

"<insert
unique name for your application>-{0}-{1}",

RoleEnvironment.CurrentRoleInstance.Id,

DateTime.UtcNow.Ticks)

).UploadText(ex.ToString());

}

}



}

Now, when your Azure role is about to crash, you’ll find an entry in your blog storage with the details of the exception that was thrown. For example, one of the leading reasons why an Azure Worker Role crashes is because it can’t find a dependency it needs. So, in that case, you’ll find an entry in your storage with the following details:

 1: System.IO.FileNotFoundException:
Could not load file or assembly 

 2: 'GuestBook_Data,
Version=1.0.0.0, Culture=neutral, 

 3: PublicKeyToken=f8a5fcb6c395f621'
or one of its dependencies. 

 4: The
system cannot find the file specified.

 5:  

 6: File
name: 'GuestBook_Data, Version=1.0.0.0, Culture=neutral, 

 7: PublicKeyToken=f8a5fcb6c395f621'

You can find some other common reasons why an Azure role might crash (especially when you first deploy it) can be found at Anton Staykov’s excellent blog:

Hope this helps.

Enjoy!

.NET 2.0 and Access Databases

Greg Varveris — Sat, 24 Jul 2010 03:51:28 GMT

For an internal application at my company, very particular users have the rights to download an MDB that contains links to a replicated instance of a DB. This was done so they could create their own queries without any assistance from IT - essentially a poor man's Cognos or Reporting Services. This worked fine in .Net 1.1.

We are currently in the process of upgrading this application to .Net 2.0 and one of the developers on the project brought to my attention that the download was failing with a message stating:

She did some research and uncovered this forum post with step by step instructions on how to re-enable the downloading of an Access database.

Please keep in mind, though, that this was done for security purposes - so any page that links to a secured Access DB - should be secured in a variety of ways:

1. Code Access Security:

 1: <PrincipalPermission(SecurityAction.Demand,
_ 

 2: Authenticated:=True,
_

 3: Role:="Secured
User")> _

This should be placed in the code-behind on the page with the link to the file. As you can see, the "Role" property will secure this page to just a user in a particular role. If you have a page that is accessible to multiple roles, you can stack the class attributes on top of each other as seen here:

 1: <PrincipalPermission(SecurityAction.Demand,
_

 2: Authenticated:=True, 

 3: Role:="First
Role")> _

 4: <PrincipalPermission(SecurityAction.Demand,
_

 5: Authenticated:=True, 

 6: Role:="Second
Role")> _

 7: Partial
Class PagesToBeSecured

2. File Access Restriction:

Also, by putting a web.config in the folder that houses the Access DB, you can secure access to the contents of a particular folder. For example with a structure of:

 1: Root/Downloads/Database/db.mdb

You can put a web.config in the "Database" folder that restricts access to that folder to a particular user/role/etc. For example, the web.config in this example would look something like:

<?xml version="1.0" encoding="utf-8"?>

<configuration>

<system.web>

<authorization>

<allow roles="Role
1" />

<allow roles="Role
2"/>

<deny users="*" />

</authorization>

</system.web>

</configuration>

As you can see, we are only allowing users in roles Role 1 and Role 2 to access the contents of this folder. If any other users attempt to access the file, they will get a Page Cannot Be found exception.

In conclusion - if you are going to remove this particular restriction in IIS to allow users to download Access DB files directly from your web application - then you shouldn't completely discount security and you implement both of the following measures.

Enjoy!

ASP.NET 2.0: Textbox ReadOnly Property

Greg Varveris — Sat, 24 Jul 2010 03:42:12 GMT

This has been documented in numerous places including here, here, here (with an incorrect fix) and here.

Essentially, if you set the Readonly Property of a textbox using either the XHTML or in the code-behind, any changes you make to the value of that textbox client-side (ie: javascript) will not be persisted across postbacks. I had found this method extremely effective for Calendar controls and what-not. You just provide a link to a popup and then when the user selects an item in the popup, you can populate the underlying Textbox with the value from the popup. Unfortunately, out of the box, that functionality has been taken away.

The code in the Textbox that actually signals to the page that textboxes using the ReadOnly property should not be saved in ViewState is in a few places:

Protected Overrides Function SaveViewState() As Object

If Not Me.SaveTextViewState Then

Me.ViewState.SetItemDirty("Text", False)

End If

Return MyBase.SaveViewState

End Function

  

Private Shadows ReadOnly Property SaveTextViewState()
_

As Boolean

Get

  

If (Me.TextMode
= TextBoxMode.Password) Then

Return False

End If

If (((MyBase.Events.Item(EventTextChanged) Is Nothing)
_

AndAlso MyBase.IsEnabled)
_

AndAlso ((Me.Visible AndAlso Not Me.ReadOnly)
_

AndAlso (MyBase.GetType Is GetType(TextBox)))) Then

Return False

End If

  

Return True

End Get

End Property

In the SaveTextViewState() method, part of the conditional statement specifies that if the ReadOnly property is set to true, then do not save the ViewState.

Also, in the LoadPostData() method, there is another check to make sure that the control's ReadOnly property is not set to true before it loads the data from the form post:

Protected Overrides Function LoadPostData(
_

ByVal postDataKey As String,
_

ByVal postCollection As _

NameValueCollection) As Boolean

MyBase.ValidateEvent(postDataKey)

Dim text As String = Me.Text

Dim text2 As String =
_

postCollection.Item(postDataKey)

If (Not Me.ReadOnly _

AndAlso Not [text].Equals(text2,
_

StringComparison.Ordinal)) Then

Me.Text
= text2

Return True

End If

  

Return False

End Function

If the ReadOnly property is set to true, then it will not set the Text property of the TextBox to be the value from the Form post.

The fix that people are touting is relatively simple. In the code behind of the page, you can simply add the attribute manually to the TextBox like this:

Protected Sub Page_Load(ByVal sender As Object,
_

ByVal e As System.EventArgs) Handles Me.Load

With Me.txtTest

.Attributes.Add("readonly", "readonly")

End With

End Sub

And while this would work - this just feels like a bandage. Plus, if you have a big web project you are converting from .net 1.1 to .net 2.0 that contains TextBoxes all over the place that have the ReadOnly=True set, then this would be a lot of code to include on every single page. Even if you have a shared function somewhere that you can call - that means you still have to call the function for each Textbox that you wish to set as ReadOnly.

An alternative is to create your own TextBox class that inherits from the existing TextBox and handles the ReadOnly property in the fashion mentioned above. Any example of the code for the new TextBox is as follows:

Namespace WebControls

Public Class TextBox

Inherits System.Web.UI.WebControls.TextBox

  

Public Overrides Property [ReadOnly]() As Boolean

Get

Return False

End Get

Set(ByVal value As Boolean)

If value Then

Me.Attributes("readonly")
= "readonly"

Else

Me.Attributes.Remove("readonly")

End If

End Set

End Property

  

End Class

End Namespace

That's fine for new TextBoxes, but what about my hundreds and hundreds of TextBoxes that are already in my application? Well, .Net 2.0 allows you to use something called tagMappings in your web.config. Essentially, they are a way to redirect the compiler to use a different class for an existing mapping when it compiles your pages. From MSDN:

"Defines a collection of tag types that are remapped to other tag types at compile time."

So, how do we use this neat feature to solve this problem? Well, in the web.config, we will tell the .Net compiler to use our new TextBox control instead of the existing System.Web.UI.WebControls.TextBox control. In order to do this, you simply add the following to your web.config:

<pages>

<tagMapping>

<add tagType="System.Web.UI.WebControls.TextBox" 

mappedTagType="WebControls.TextBox"/>

</tagMapping>

</pages>

The tagType attribute is the existing tag you would like to change (System.Web.UI.WebControls.TextBox) and the mappedTagType is the new TextBox control from above.

With this tag added in the web.config - whenever you have the following in a page:

<asp:TextBox runat="server" 

ID="txtTest" 

ReadOnly="true" />

Your application will use the TextBox defined directly above.

Enjoy!