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VB.Net WinForms Application Main Form Loading with Splash Screen

Posted on 2015-01-27
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I have a VB.NET WinForms application with a splash screen containing a progress bar which I can successfully update during the Load event of the Main Form (formMain).  This was accomplished by reviewing the following article:

http://www.experts-exchange.com/Programming/Languages/.NET/Visual_Basic.NET/A_3671-Updating-a-Splash-Screen-with-Loading-Progress-in-a-VB-Net-WinForms-Application.html

How can I determine what is occurring in my application prior to the formMain_Load() event being triggered?  The splash screen is visible and active for 15 seconds prior to reaching the breakpoint at the first line of the MyBase.Load event of formMain.  Afterwards, everything is as expected.  What is happening during this time prior to the main form getting loaded?  Any information is greatly appreciated.  Thank you for your time and help.

Christopher
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Question by:chmarch
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by:it_saige
it_saige earned 250 total points
ID: 40573218
It really depends on your application and the framework used.  However in a nutshell. when your application is compiled, a PE executable is generated.  This PE application contains:
An entrypoint (usually Main).
A list of dependencies as dynamic libraries (which includes MSCOREE.DLL;  the .NET Common Object Runtime Execution Engine).
Additional metadata including the targeted .NET runtime version

When a user starts the application (by clicking on it, running it from a command line, etc.), the Windows loader implementation (in NTDLL.dll) takes over.  The loader code is responsible for putting the executable into memory, loading any dynamic link libraries, mapping any linked libraries into a place that the executable code can reach them and updating the Import Address Table.

Once this is all completed, the loader jumps to the defined entry point.  The entry point  goes to mscoreee.dll which was mapped into the processes memory.  MSCOREE.DLL looks at the metadata loaded from the PE executable (specifically the CLR header and targeted .NET runtime version).  From that it can bind the the correct CRL version using CorBindToRuntimeEx2.

CorBindToRuntimeEx2 loads the correct .NET runtime implementation (and returns a pointer to a COM interface allowing you to invoke that .NET runtime).  This code is loaded from the dlls in %WINDIR%\Microsoft.NET\Framework\{associated version number}

At this point, the MSCORREE shim uses the .NET ICLRRuntimeHost interface point to invoke the methods needed to initialize the .NET runtime, garbage collector, IL interpreter, JIT and IHostControl interfaces (that allow the .NET interpreter to talk back to the hosting process).  Finally, mscoree tells the IL interpreter to start executing your compiled application's IL code.Example of a comipled IL Manifest file (contains .NET runtime version, dependencies, resources and other metadata)Example IL Main entrypoint.The amazing thing is that all of the above, *usually*, happens in a matter of milliseconds.

The unfortunate thing, is that you cannot have a .NET Splash Screen for the above process as it is basically an unmanaged bootstrapper process and ultimately outside of the control of .NET.

-saige-
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Mike Tomlinson earned 250 total points
ID: 40573250
Do a search for "Cold versus Warm Start of .Net" to get an idea of what you're dealing with.  Basically it is .Net itself that is loading and then any specific assemblies needed for your app.

Process Explorer: https://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
Improving Application Startup Time: https://msdn.microsoft.com/en-us/magazine/cc163655.aspx
Application Startup Time: https://msdn.microsoft.com/en-us/library/cc656914(v=vs.110).aspx
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