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using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
namespace Pfz.Threading
{
/// <summary>
/// Class similar to Lazy. But instead of only loading values when they are first accessed, it tries to load the
/// value when the application is idle. Will load immediatelly if the value is requested.
/// You must instantiate the generic version.
/// </summary>
public abstract class BackgroundLoader:
ThreadSafeDisposable
{
private static readonly ManagedAutoResetEvent _event = new ManagedAutoResetEvent();
internal static readonly HashSet<BackgroundLoader> _items = new HashSet<BackgroundLoader>();
static BackgroundLoader()
{
Thread thread = new Thread(_Run);
thread.Name = "Pfz.Threading.BackgroundLoader";
thread.Start();
}
private static void _Run()
{
var currentThread = Thread.CurrentThread;
while(true)
{
currentThread.IsBackground = true;
#if !SILVERLIGHT
currentThread.Priority = ThreadPriority.Lowest;
#endif
_event.WaitOne();
while(true)
{
#if !SILVERLIGHT
while(true)
{
// Keeps yielding while there are other threads wanting to run.
if (!Thread.Yield())
break;
}
currentThread.Priority = ThreadPriority.Normal;
#endif
currentThread.IsBackground = false;
BackgroundLoader item;
lock(_items)
{
item = _items.FirstOrDefault();
if (item == null)
break;
_items.Remove(item);
}
try
{
lock(item.DisposeLock)
if (!item.WasDisposed)
item._CreateValue();
}
catch
{
// Ignore any exceptions here.
}
currentThread.IsBackground = true;
#if !SILVERLIGHT
currentThread.Priority = ThreadPriority.Lowest;
#endif
}
}
}
internal BackgroundLoader()
{
lock(_items)
_items.Add(this);
_event.Set();
}
/// <summary>
/// Clears the loaded value or removes this BackgroundLoader from the
/// pending objects to load.
/// </summary>
protected override void Dispose(bool disposing)
{
if (disposing)
_ClearValueOrRemoveFromLoader();
base.Dispose(disposing);
}
internal abstract void _CreateValue();
internal abstract void _ClearValueOrRemoveFromLoader();
}
/// <summary>
/// Class similar to Lazy. But instead of only loading values when they are first accessed, it tries to load the
/// value when the application is idle. Will load immediatelly if the value is requested.
/// </summary>
public sealed class BackgroundLoader<T>:
BackgroundLoader,
IValueLoader<T>
where
T: class
{
private Func<T> _createDelegate;
/// <summary>
/// Creates a new background loader that will create the value using the default constructor.
/// </summary>
public BackgroundLoader()
{
}
/// <summary>
/// Creates a new BackgroundLoaderByDelegate setting the delegate used
/// to create the Value.
/// </summary>
public BackgroundLoader(Func<T> createDelegate)
{
_createDelegate = createDelegate;
}
internal override void _CreateValue()
{
if (_value != null)
return;
if (_createDelegate != null)
{
_value = _createDelegate();
_createDelegate = null;
}
else
_value = (T)Activator.CreateInstance(typeof(T));
}
private T _value;
/// <summary>
/// Gets the Value, creating it immediatelly if needed.
/// </summary>
public T Value
{
get
{
T result = _value;
if (result != null)
return result;
lock(DisposeLock)
{
if (WasDisposed)
return null;
result = _value;
if (result != null)
return result;
lock(_items)
_items.Remove(this);
_CreateValue();
return _value;
}
}
}
/// <summary>
/// Gets the value that is actually in memory.
/// If the value was not created or if this object was disposed, returns null.
/// </summary>
public T InMemoryValue
{
get
{
return _value;
}
}
internal override void _ClearValueOrRemoveFromLoader()
{
T value = _value;
if (value == null)
{
_createDelegate = null;
lock(_items)
_items.Remove(this);
return;
}
_value = null;
var disposable = value as IDisposable;
if (disposable != null)
disposable.Dispose();
}
}
}
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I started to program computers when I was 11 years old, as a hobbyist, programming in AMOS Basic and Blitz Basic for Amiga.
At 12 I had my first try with assembler, but it was too difficult at the time. Then, in the same year, I learned C and, after learning C, I was finally able to learn assembler (for Motorola 680x0).
Not sure, but probably between 12 and 13, I started to learn C++. I always programmed "in an object oriented way", but using function pointers instead of virtual methods.
At 15 I started to learn Pascal at school and to use Delphi. At 16 I started my first internship (using Delphi). At 18 I started to work professionally using C++ and since then I've developed my programming skills as a professional developer in C++ and C#, generally creating libraries that help other developers do their work easier, faster and with less errors.
Want more info or simply want to contact me?
Take a look at:
http://paulozemek.azurewebsites.net/
Or e-mail me at: paulozemek@outlook.com
Codeproject MVP 2012, 2015 & 2016
Microsoft MVP 2013-2014 (in October 2014 I started working at Microsoft, so I can't be a Microsoft MVP anymore).