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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for July 5th, 2012

Dear fellow programmer. If you aren’t experienced doing multi-threading, please don’t!

Posted by jpluimers on 2012/07/05

Recently I was asked to investigate a performance problem with a certain .NET application.

The first error I got when getting the app to build in Visual Studio 2010, and then run it was like this:

System.ComponentModel.InvalidAsynchronousStateException was caught
  Message=An error occurred invoking the method.  The destination thread no longer exists.
  Source=System.Windows.Forms
  StackTrace:
       at System.Windows.Forms.Control.WaitForWaitHandle(WaitHandle waitHandle)
       at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
       at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args)
       at UI.Splash.SetStatus(String status) in C:\...\Splash.cs:line 395
       at UI.Menu.Main() in C:\...\Menu.cs:line 4275
  InnerException:

Someone built their own splash logic with multi-threading.

Funny that today, this got answered on StackOverflow by mgiemultithreading – TMonitor synchronization / Application.ProcessMessages – Stack Overflow.

Though that is a Delphi link (and points to the nice libraries AsynCalls and OmniThreadLibrary), the most important link it contains is to Borland Newsgroup Archive :: borland.public.delphi.internet.winsock :: Re: Disconnect TIdHttp in thread.

That sounds like a Delphi link too, but the subtitle “‘Ways to get into avoidable trouble with threads, V1.2′” hints the essence: it is a post that describes in an environment-agnostic way how to avoid multi-threading problems.

Recommended reading!

Anyway: Building multi-threaded code is hard. Even harder fleshing out all the corner cases and potential error conditions.

No matter what kind of programming environment: If you have not done lots of multi-threaded programming, then please don’t do it yourself: go ask someone that does know how to do it. Or better, try to avoid it.

I try to let libraries to the handling of multi-threading for me, if I use multi-threading at all, as others are far better at this than I am.

–jeroen

Posted in .NET, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Delphi, Development, Java, Software Development, VB.NET, VBS, Visual Studio 2010, Visual Studio and tools, WinForms | 6 Comments »

.NET/C# – finding the attribute values for an assembly

Posted by jpluimers on 2012/07/05

For some version management features, I needed to find the attribute values of loaded assemblies. Googling around, I didn’t find many nice solutions. In fact the solutions I found didn’t work well (AssemblyName is not an Attribute!), and/or contained lots of duplicate code, or uses RegEx and other string comparisons (lesson: if you can do it with either string comparison or proper type checking, use the latter). Below is the code; here some explanation:

  • It uses a C# translation of the RetrieveLinkerTimestamp function found through Jeff Atwood (Coding Horror) which was published by Kevin Gearing and determines the linker timestamp from the PE Header. It corrects the time into your time zone. The C# version has two overloads (one with an Assembly parameter, the other with a string filePath), and the latter now contains some exception handling just in case you pass it nonsense.
  • The RunOnAssemblyAttribute generic method takes a T parameter of type Attribute, then runs the Action<T> action if that attribute is found in the Assembly assembly. It retreived the attribute using the Assembly.GetCustomAttributes method.
  • When a null parameter is passed, it gets the information from the executing assembly (if you want it to be another one, just change the code if you want it to)
    An alternative way of getting the executable name is at the very bottom: you need it when your assembly is loaded from an unmanaged application (GetEntryAssembly then returns null)
  • The constructor runs it on all known assembly related attributes in the System.Reflection namespace, calling RunOnAssemblyAttribute with an action that fills the property for each existing attribute (you wish all those attributes would have a Value property, but their property names are specific for each attribute). For non existing attributes, the default property values are used (which incidently are the default values for those attributes anyway).
  • There are a couple of casts (for instance AssemblyNameFlags) as the underlying attribute contains a constructor with that parameter (in this case AssemblyFlagsAttribute), but stores it in an integer without providing a cast property. Maybe there should be proper type checking; that is left as an exercise…
  • The constructor also fills a couple of non attribute properties – AssemblyName – LinkerTimestamp
  • The Name property is derived from the AssemblyName.Name property if it exists

Read the rest of this entry »

Posted in .NET, C#, C# 3.0, C# 4.0, C# 5.0, Development, Software Development | Leave a Comment »

 
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