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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011 CPOL
This article will present two alternatives to Lazy.
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
Pfz
Caching
Collections
DataTypes
DynamicObjects
Internal
Extensions
Factoring
Pfz.csproj.user
Pfz.Phone.csproj.user
Pfz.ruleset
Pfz.Silverlight.csproj.user
Pfz.snk
Pfz.suo
PhoneSpecific
Properties
Remoting
Instructions
Internal
Serializers
Udp
Serialization
BinaryBuiltIn
Threading
Contexts
Disposers
Unsafe
using System;
using System.Diagnostics;
using System.Threading;

namespace Pfz.Threading.Unsafe
{
	/// <summary>
	/// Class that creates a Timer that runs an action at given intervals.
	/// It is high precision (and cpu intensive). It tries to compensate slowdowns, but never stacks.
	/// </summary>
	public sealed class UnsafeHighPrecisionTimer:
		IAdvancedDisposable
	{
		private int _threadId;
		private bool _wasDisposed;

		/// <summary>
		/// Creates a new timer that will run the given action at the given interval milliseconds.
		/// If exclusiveThreadName is not null, then a new Thread will be created. Otherwise, a 
		/// UnlimitedThreadPool thread will be used.
		/// </summary>
		public UnsafeHighPrecisionTimer(Action action, double interval, string exclusiveThreadName=null):
			this(action, TimeSpan.FromMilliseconds(interval), exclusiveThreadName)
		{
		}

		/// <summary>
		/// Creates a new timer that will run the given action at the given interval milliseconds.
		/// If exclusiveThreadName is not null, then a new Thread will be created. Otherwise, a 
		/// UnlimitedThreadPool thread will be used.
		/// </summary>
		public UnsafeHighPrecisionTimer(Action action, TimeSpan interval, string exclusiveThreadName=null)
		{
			if (action == null)
				throw new ArgumentNullException("action");

			if (interval <= TimeSpan.Zero)
				throw new ArgumentOutOfRangeException("interval must be greater than 0.");

			Action = action;
			Interval = interval;

			if (exclusiveThreadName == null)
				UnlimitedThreadPool.Run(_Run);
			else
			{
				Thread thread = new Thread(_Run);
				thread.Name = exclusiveThreadName;
				thread.Start();
			}
		}

		/// <summary>
		/// Releases the Timer thread immediatelly.
		/// Note that, if such thread is already running, it will continue to the end of the action,
		/// and only then will be returned to the pool, but the Timer will return immediatelly.
		/// </summary>
		public void Dispose()
		{
            if (_wasDisposed)
				return;

			_wasDisposed = true;

			if (Thread.CurrentThread.ManagedThreadId == _threadId)
				return;

			Thread.MemoryBarrier();

			while(_threadId != -1)
			{
				Thread.Yield();
				Thread.MemoryBarrier();
			}
		}

		/// <summary>
		/// Throws an exception if this object was already disposed.
		/// </summary>
		private void _CheckUndisposed()
		{
			if (WasDisposed)
				throw new ObjectDisposedException(GetType().FullName);
		}

		/// <summary>
		/// Gets a value indicating if this object was already disposed.
		/// </summary>
		public bool WasDisposed
		{
			get
			{
				return _wasDisposed;
			}
		}

		/// <summary>
		/// Gets the action that's run by this timer.
		/// </summary>
		public Action Action { get; private set; }

		/// <summary>
		/// Gets the interval in which the action is run.
		/// </summary>
		public TimeSpan Interval { get; private set; }

		private void _Run()
		{
			var currentThread = Thread.CurrentThread;
			_threadId = currentThread.ManagedThreadId;

			Stopwatch stopwatch = null;
			try
			{
				TimeSpan nextInterval = Interval;
				stopwatch = new Stopwatch();
				while(true)
				{
					stopwatch.Reset();
					stopwatch.Start();
					Action();

					if(stopwatch.Elapsed < nextInterval)
					{
						currentThread.IsBackground = true;

						while(stopwatch.Elapsed < nextInterval)
						{
							if (_wasDisposed)
								return;

							Thread.Yield();
						}

						currentThread.IsBackground = false;
					}
					else
					if (_wasDisposed)
						return;

					stopwatch.Stop();

					TimeSpan lastActionTime = stopwatch.Elapsed - nextInterval;
					nextInterval = Interval - lastActionTime;
					if (nextInterval < TimeSpan.Zero)
						nextInterval = TimeSpan.Zero;
				}
			}
			finally
			{
				currentThread.IsBackground = false;

				if (stopwatch != null)
					stopwatch.Stop();

				_threadId = -1;
				Thread.MemoryBarrier();
			}
		}
	}
}

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About the Author

Paulo Zemek
Engineer Microsoft Corporation
United States United States
I started to program computers when I was 11 years old, as a hobbist, 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 they work easier, faster and with less errors.

Now I just started working as a Senior Software Engineer at Microsoft.

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 (now I work at Microsoft so I can't be a Microsoft MVP anymore)

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