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Lazy Alternatives - LazyAndWeak and BackgroundLoader

, 1 Dec 2011
This article will present two alternatives to Lazy.
LazyAlternatives.zip
LazyAlternatives
LazyAlternatives.suo
LazyAlternativesSample
Properties
Settings.settings
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.Threading;

namespace Pfz.Threading.Unsafe
{
	/// <summary>
	/// Class that creates a Timer that runs an action at given intervals.
	/// The intervals are always counted after the end of the last action, so it does not stack or tries to
	/// compensate delays.
	/// </summary>
	public sealed class UnsafeNonStackingTimer:
		IAdvancedDisposable
	{
		private ManagedManualResetEvent _manualResetEvent = new ManagedManualResetEvent();
		private int _threadId;

		/// <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 UnsafeNonStackingTimer(Action action, int interval, bool runImmediatelly=false, string exclusiveThreadName=null)
		{
			if (action == null)
				throw new ArgumentNullException("action");

			if (interval < 1)
				throw new ArgumentOutOfRangeException("interval must be greater than 0.");

			Action = action;
			Interval = interval;

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

		/// <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()
		{
			var manualResetEvent = _manualResetEvent;
            if (manualResetEvent == null)
				return;

			if (Thread.CurrentThread.ManagedThreadId == _threadId)
			{
				manualResetEvent.Set();
				return;
			}

			lock(manualResetEvent)
			{
				if (_manualResetEvent == null)
				{
					// if the manualResetEvent was just set to null, return.
					return;
				}

                manualResetEvent.Set();
			}

			do
			{
				#if WINDOWS_PHONE
					Thread.Sleep(1);
				#else
					Thread.Yield();
				#endif

				Thread.MemoryBarrier();
			} while (_manualResetEvent != null);
		}

		/// <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
			{
				var manualResetEvent = _manualResetEvent;

				try
				{
					return manualResetEvent == null || manualResetEvent.WaitOne(0);
				}
				catch
				{
					return true;
				}
			}
		}

		/// <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 int Interval { get; private set; }

		private void _Run(object runImmediatelly)
		{
            var manualResetEvent = _manualResetEvent;
			var currentThread = Thread.CurrentThread;
			_threadId = currentThread.ManagedThreadId;

			try
			{
				if ((bool)runImmediatelly)
					Action();

				while(true)
				{
					currentThread.IsBackground = true;
					if (manualResetEvent.WaitOne(Interval))
						return;

					currentThread.IsBackground = false;
					Action();
				}
			}
			finally
			{
				currentThread.IsBackground = false;

				lock(manualResetEvent)
				{
					_manualResetEvent = null;
					manualResetEvent.Dispose();
				}
			}
		}
	}
}

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About the Author

Paulo Zemek
Architect
Canada Canada
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.
 
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
Microsoft MVP 2013

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