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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.IO.MemoryMappedFiles;
using System.Threading;

namespace Pfz.Remoting
{
	/// <summary>
	/// This class represents a communication stream based on MemoryMappedFiles. It only works locally, but
	/// is faster than TCP/IP or NamedPipes.
	/// </summary>
	public sealed class MemoryMappedFileWriter:
		IDisposable
	{
		private MemoryMappedFile _file;
		private MemoryMappedViewAccessor _accessor;
		private EventWaitHandle _sentEvent;
		private EventWaitHandle _readEvent;
		private int _mappedFileLength;
		private unsafe byte *_pointer;
		private unsafe MemoryMappedFileReaderWriterData *_data;
		private bool _eventSet;

		/// <summary>
		/// Creates a new MemoryMappedFileWriter with the given name and length, and optionally with the given
		/// timeout, which will be the time it will wait for client connections.
		/// </summary>
		public MemoryMappedFileWriter(string name, int length, int connectionTimeout = -1)
		{
			if (name == null)
				throw new ArgumentNullException("name");

			if (length <= 0)
				throw new ArgumentOutOfRangeException("length");

			if (connectionTimeout < -1)
				throw new ArgumentOutOfRangeException("connectionTimeout");

			unsafe
			{
				_file = MemoryMappedFile.CreateNew(name, length + sizeof(MemoryMappedFileReaderWriterData));
				_accessor = _file.CreateViewAccessor();
				byte *pointer = null;
				_accessor.SafeMemoryMappedViewHandle.AcquirePointer(ref pointer);
				(*(int *)pointer) = length;
				_mappedFileLength = length;

				_pointer = pointer;
				_data = (MemoryMappedFileReaderWriterData *)(pointer + length);
			}
			_accessor.Flush();

			_sentEvent = new EventWaitHandle(false, EventResetMode.AutoReset, name + ":Sent");
			_sentEvent.Set();

			_readEvent = new EventWaitHandle(false, EventResetMode.AutoReset, name + ":Read");
			if (!_readEvent.WaitOne(connectionTimeout))
				throw new TimeoutException("Timed-out waiting for client connection.");
		}

		/// <summary>
		/// Releases all resources used by this Memory-Mapped-File.
		/// </summary>
		public void Dispose()
		{
			var sentEvent = _sentEvent;

			unsafe
			{
				if (_data != null && sentEvent != null)
				{
					_data->_ended = true;

					sentEvent.Set();
				}
			}

			var accessor = _accessor;
			if (accessor != null)
			{
				_accessor = null;
				accessor.Dispose();
			}

			var file = _file;
			if (file != null)
			{
				_file = null;
				file.Dispose();
			}

			if (sentEvent != null)
			{
				_sentEvent = null;
				sentEvent.Dispose();
			}

			var readEvent = _readEvent;
			if (readEvent != null)
			{
				_readEvent = null;
				readEvent.Dispose();
			}
		}

		private int _timeout = 60000;
		/// <summary>
		/// Gets or sets the time-out used for writes.
		/// This is not the same as the connection time out and must be set explicity.
		/// </summary>
		public int Timeout
		{
			get
			{
				return _timeout;
			}
			set
			{
				if (value < -1)
					throw new ArgumentOutOfRangeException("value");

				_timeout = value;
			}
		}

		/// <summary>
		/// Gets the Length of the memory-mapped-file.
		/// </summary>
		public int MemoryMappedFileLength
		{
			get
			{
				return _mappedFileLength;
			}
		}

		/// <summary>
		/// Writes the buffer data.
		/// </summary>
		public void Write(byte[] buffer)
		{
			if (buffer == null)
				throw new ArgumentNullException("buffer");

			_Write(buffer, 0, buffer.Length);
		}

		/// <summary>
		/// Writes the buffer data.
		/// </summary>
		public void Write(byte[] buffer, int offset)
		{
			if (buffer == null)
				throw new ArgumentNullException("buffer");

			if (offset < 0 || offset >= buffer.Length)
				throw new ArgumentOutOfRangeException("offset");

			_Write(buffer, offset, buffer.Length - offset);
		}

		/// <summary>
		/// Writes the buffer data.
		/// </summary>
		public void Write(byte[] buffer, int offset, int count)
		{
			if (buffer == null)
				throw new ArgumentNullException("buffer");

			if (offset < 0 || offset > buffer.Length)
				throw new ArgumentOutOfRangeException("offset");

			if (count < 0 || offset + count > buffer.Length)
				throw new ArgumentOutOfRangeException("count");

			_Write(buffer, offset, count);
		}
		private void _Write(byte[] buffer, int offset, int count)
		{
			unsafe
			{
				while(count > 0)
				{
					int writerPosition = _data->_writerPosition;
					bool writerState = _data->_writerState;
					int readerPosition;
					bool readerState;

					while (true)
					{
						readerPosition = _data->_readerPosition;
						readerState = _data->_readerState;

						if (writerPosition != readerPosition || writerState == readerState)
							break;

						_eventSet = false;
						_sentEvent.Set();
						if (!_readEvent.WaitOne(_timeout))
							throw new TimeoutException("Write timed-out.");
					}

					int remaining;
					if (readerState == writerState)
						remaining = _mappedFileLength - writerPosition;
					else
						remaining = readerPosition - writerPosition;

					int toSend = Math.Min(count, remaining);
					fixed(byte *sourcePointer = buffer)
						UnsafeBuffer.BlockCopy(sourcePointer + offset, _pointer + writerPosition, toSend);

					offset += toSend;
					count -= toSend;

					writerPosition += toSend;
					if (writerPosition >= _mappedFileLength)
					{
						writerPosition = 0;
						_data->_writerState = !writerState;
					}

					_data->_writerPosition = writerPosition;

					if (!_eventSet)
					{
						_eventSet = true;
						_sentEvent.Set();
					}
				}
			}
		}

		/// <summary>
		/// Tells the other side that it can start reading.
		/// </summary>
		public void Flush()
		{
			_sentEvent.Set();
		}

		/// <summary>
		/// Writes a single byte of data.
		/// </summary>
		public void WriteByte(byte value)
		{
			unsafe
			{
				int writerPosition = _data->_writerPosition;
				bool writerState = _data->_writerState;

				while (writerPosition == _data->_readerPosition && writerState != _data->_readerState)
				{
					_eventSet = false;
					_sentEvent.Set();
					if (!_readEvent.WaitOne(_timeout))
						throw new TimeoutException("Write timed-out.");
				}

				_pointer[writerPosition] = value;

				writerPosition ++;
				if (writerPosition >= _mappedFileLength)
				{
					writerPosition = 0;
					_data->_writerState = !writerState;
				}

				_data->_writerPosition = writerPosition;

				if (!_eventSet)
				{
					_eventSet = true;
					_sentEvent.Set();
				}
			}
		}
	}
}

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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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 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.

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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