Selfelected

Threading in C# by Albahari gratis

Advise: before attempting parallel programming – read up on the subject!

Normally we program by intellisense and the assumption that the name of the method does what we suppose it does.  It can be thought of as lazy, that we don’t grok the framework before we start using it.  But is does seem to work.

This is not the case with parallel programming.  Do it without understanding it and you’re down the slippery slope.

Download the Threading chapter of C#4 in a nutshell by Albahari.  It is gratis.
Read up.  The text is easy to read and well written.

I have read one other part (looking for interface and inheritance and virtual) of the first release and it was also good.  If the rest of the book is as well written I suggest everyone to get a copy.

Exception: Only parameterless constructors and initializers are supported in LINQ to Entities.

I am not sure of the *exact* meaning and reason for this but I found something that can be good to know.  Or not.

return context.NuggetSet.Where(n => n.Name == name).Select(x => new MyClass(x)).ToList();

threw a

Only parameterless constructors and initializers are supported in LINQ to Entities.

When inserting a ToList it worked as suspected/wanted.

return context.NuggetSet.Where(n => n.Name == name).ToList().Select(x => new MyClass(x)).ToList();

My guess is that by calling ToList we losen EF’s grip of the entities and can do what we want with it.

CompulsoryCat 1.1

Just released version 1.1 of CompulsoryCat on google code.

It is a helper lib for getting the names of methods, classes, properties and other stuff out of the methods, classes etc.  It uses lambda or reflection to be as safe as possible.

It is unit tested and has a small exe to show a few examples of its use.  There is also a help file.

Exception: Error 1083: The executable program that this service is configured to run in does not implement the service.

In short: verify that the service name is correct.  Totally correct.

Longer:

Debugging windows services written in dotnet can be hard.  They have no GUI and have to be installed by a semi secret process.  Then they have to be started by a system call.  And if the start fails it is not necessarily possible to uninstall the service without rebooting.  The CL.exe doesn’t work and hacking the registry doesn’t work.

Today I spent hours tracking down a bug that surfaced with a “Error 1083: The executable program that this service is configured to run in does not implement the service.” when starting the service.  In the end I found out that the ServiceName was incorrect.

To be honest I got some clues, in one place it said MyMailer instead of MyMailerService.  I couldn’t be sure if this was correct or not since I had inherited the project and my search turned out nothing so I dropped it.

By (almost) chance I checked into the automagically created MyMail.designer.cs file and noticed this.ServiceName=”MyMailer”.  Which, it turned out, was the culprit.

I learned a trick on the way.  The service has 30 (I believe) seconds to start.  If it doesn’t fulfill it is shot down by Windows.  When I started the process it failed and I got a question whether I wanted to debug it.  Unfortunately it takes more thatn 30 s to open my VS2010.  So I started VS as administrator (necessary in Win7) and loaded the project.  When I then started the service I got the question whether to attach and I did.  Two seconds of work and I got a highlighted row at the exact point.

A .NET Framework error occurred during execution of user-defined routine or aggregate “XXX”: System.InvalidOperationException: The context connection is already in use.

If you are working with CLR in SQLServer you might run into

A .NET Framework error occurred during execution of user-defined routine or aggregate "MyCLRMethod":   System.InvalidOperationException: The context connection is already in use.

I cannot say this is the solution every time but it worked for me.  Look down to the top of the stack (furthest down in the text) and you get some more clues.

Msg 6522, Level 16, State 1, Line 1
A .NET Framework error occurred during execution of user-defined routine or aggregate "MyCLRMethod":
System.InvalidOperationException: The context connection is already in use.
System.InvalidOperationException:
 at System.Data.SqlClient.SqlInternalConnectionSmi.Activate()
 at System.Data.SqlClient.SqlConnectionFactory.GetContextConnection(SqlConnectionString options, Object providerInfo, DbConnection owningConnection)
 at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection)
 at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup)
 at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
 at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
 at System.Data.SqlClient.SqlConnection.Open()
 at Elvis.DatabaseCLR.UserDefinedFunctions.GetNextSampleID(DateTime readDate, Int32 meterID, Boolean useNextMeter)
 at Elvis.DatabaseCLR.UserDefinedFunctions.ConsumptionForNewMeter(Int32 sampleID, DateTime readDate, Int32 meterID, Decimal meterCoefficient, Int32 previousMeterConsumption, DateTime presentationDateOfSample)
 at Elvis.DatabaseCLR.UserDefinedFunctions.MyCLRMethod(Int32 sampleID, DateTime presentationDate, DateTime readDate, Int32 meterID, Decimal meterCoefficient, Boolean newMeter)

.

The MyCLRMethod calls two more methods until Open is called.  Playing around I found that I couldn’t open a connection if one already was open.  It sounds right since one of the deals with CLR in SQLServer is that we already have a connection.  The resolution is to tidy up the code so we only open the connection once, or open/closes it over and over again.

Tricks I used:
– When you get the error in your applicaiton copy the SQL string to your query editor and run it from there.
– Press F5 in Visual studio and have Visual studio deploy the CLR for you.  But use the query tool to run the query.  The error message is the same.
– Debug-through-printf, or “throw exception” in this case.  Drop in a throw-exception to find out exactly which Open call is failing.  The F5-and-wait and then run query takes a while.  If you have a logging possibility it is handy now.

Cancel a tab change in Dotnet Winforms

For Dotnet2 and lower there was no easy way of stopping a user from switching a tab in a tab control.  I have written a solution in Dotnet compact framework (2?) that inherited from TabControl and overrided a couple of methods that together with a flag or two made it possible to cancel tab switching.  If I recall correctly it never stopped the control from blinking but it did it’s job.  It wasn’t hard but it took some hours.  If you are forced to implement this in Dotnet2 you have to inherit, the overridable methods used do not all send an event.

With Dotnet 3 to the current 4 it is easier.  Just associate a method with the Selecting event.

I did it in Dotnet3.5 and noticed some flickering when trying to, and cancelling, the change of tab.

Cannot serialize

Or Can’t serialise – whatever you prefer.

When using Dotnet and the built in serialiser from Microsoft it sometimes doesn’t work.  Just so.  To make it more complex the error message sometimes doesn’t say anything either, just something like FileNotFoundException.  Sucks.

One solution might be to use the XmlSerializerPreCompiler tool from SellsBrothers available gratis and with source code.  It is downloadable here.  The download is dotnet2 but I updated it to 3.5 easily with Visual Studio 2010.

There is GUI called XmlPreCompiler for it too.

You might run into that the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion as to have a DWord called EnableLog set to 1.  The XmlPreCompiler has to be restarted to understand this key has changed.

If you are working with Dotnet > 2 you have to compile the GUI from source.  It is not difficult – the Visual Studio solution file is in the source code.

When running the GUI tool and your assembly is referring to another assembly (DLL has reference to other DLL) it is important that the GUI tool’s exe is in the same folder as the assemblies you are looking at.  Unless the other assemblies are in the GAC I suppose…

Note that you might have to restart Visual Studio 2010 when up/down grading dotnet version.  It seems like VS holds reference to files with the earlier version.  This has happened to me both when downgrading 4->3.5 and upgrading 2->3.5.

This was a lot of chatter about the apps and problem but I ran into them all right now.  And if You are here – so might you.  Happy hacking!

(My problem in this case was that I had set Visual studio to break on all thrown exceptions.  Took me six hours to figure out…)

CREATE ASSEMBLY failed because method ‘…’ on type ‘…’ in safe assembly ‘…’ is storing to a static field. Storing to a static field is not allowed in safe assemblies.

When working with CLR inside the SQLserver database one doesn’t have to deploy the DLL through Visual Studio.  Instead use the Create Assembly command.

There are several reasons for this command to fail and

CREATE ASSEMBLY failed because method 'AAA' on type 'BBB' in safe assembly 'CCC' is storing to a static field.
Storing to a static field is not allowed in safe assemblies.

is one of them.

Unless your assembly is very complex the diagnosis is easy.  The AAA is a static something.  If it is a property

public static Colour{ get; set; }

AAA will be

set_Colour

CCC is the assembly that refuses to install.

Find AAA.  Rewrite to be not static.  Compile.  Run create assembly again.

throw;

Avoid

try{
    ...
}catch( Exception exc ){
    ...
 throw exc;
}

since it destroys the exception stack.

Instead write

try{
    ...
}catch( Exception ){
    ...
 throw;
}

If you don’t understand what “destroying the exception stack” means you probably don’t want to destroy it and this recommendation is even more something to heed.

To get to the exception use $exception.

$exception and $ReturnValue

In dotnet one can write

try{
    ...
}catch(Exception){
   throw;
}

which gives two debugging tools.  The first is the ability to set a break point on the catch line.

Note how I haven’t written catch( Exception exc) but only catch( Exception).  This makes us avoid a compiler warning because we don’t use the exc variable.  Which brings us to trick number two in Visual studio: Since we don’t have a variable with the exception instead write $exception in the immediate window or the quickwatch window.  $exception brings forward the [hidden] exception reference.

Also note how there is no variable behind the throw statement.  This makes the framework hide the catch/throw and leave the stack intact.

Update: In VisualStudio2010 it looks like it is enough to write exception in the quickwatch window.

With dotnet 4.5.1? one can write $ReturnValue the same way to get to the… the… the… return value!