VB'NET CLR

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VB.NET CLR

• Richard Vantrease

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Introduction

• The .NET Common Language Runtime (CLR) is the
  language runtime that all of the .NET languages
  use. VB used to require its own runtime files.
• msvbvm60.dll was the main runtime file for VB 6.0.

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Vocabulary

• Assemblies (DLL or EXE)
• Manifest
• Modules
• Types
• .NET Metadata
• Attributes
• Deployment
• Managed Code
• Finalize Method
• Garbage Collector
• Managed Heap

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Assemblies

• An assembly is the primary unit of deployment for
  a .NET application.
• Assemblies contain modules, a manifest and
  resource files.
• Assemblies can only have one manifest.

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Modules

• Modules are some of the files that make up an
  assembly (EXEs and DLLs).
• Modules contain types (similar to classes in
  VB6), metadata, and optionally the assembly
  manifest.
• Types are made up of Fields, Methods and
  Properties.

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.NET Assembly Manifest

• Manifest is stored in an EXE, DLL or a standalone
  portable execution (PE) file.
• The manifest contains assembly metadata.
• The assembly manifest
• Lists files that make up the assembly
• Maps location of types and resources
• Enumerates other assembly dependencies
• Self describes the assembly

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Deployment

• Deployment of a VB.NET assembly is much easier
  than deploying a VB6 application.
• VB.NET assemblies are self describing and
  therefore do not need to be registered. The .NET
  framework searches for referenced assemblies
  automatically.
• .NET also supports side by side execution (use of
  different versions of the same component).

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Managed Code

• Managed code is any code that executes in the
  CLR.
• Code which is not in the .NET framework and does
  not use the CLR is un-managed code.

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Garbage Collector

• The garbage collector (GC) periodically goes
  through all the objects in use by the CLR and
  eliminates or destroys the ones that no longer
  are in use.
• The GC, not the programmer, determines when an
  object is destroyed.
• The GC uses nondeterministic finalization.

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Finalize Method

• Object.Finalize is the method that the GC calls
  immediately before collecting and destroying the
  object.
• Sometimes it is necessary to override the
  finalize method in order to free up expensive
  resources or to more closely control the time
  when object clean-up occurs.

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Overriding The Finalize Method

• Protected Overrides Sub Finalize()
• Cleanup code goes here
• End Sub
• Suppress normal finalize call
• GC.SuppressFanalize(Me)

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Managed Heap

• The CLR uses the GC to manage the heap.
• The heap is where objects are created in memory.
• The .NET CLR uses a managed heap which means it
  keeps track of the objects allocated in the heap.

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Heap Optimizations

• Objects that are allocated on the heap are
  assigned generations (0 2).
• Each time the GC runs if it does not collect an
  object, the objects generation is incremented.
• The GC tries to collect objects with the lowest
  generation numbers first.
• When the GC is done collecting objects it
  compacts the heap so it does not become
  fragmented.