C# 4 and .NET 4

Mapped-Memory files ❘ 799
figure 29-12
maPPed-memory files
If you have been working your entire coding life with only managed code, then mapped-memory files might
be a brand new concept. .NET Framework 4 now supplies mapped-memory files as part of your toolkit for
building applications with the introduction of the System.IO.MemoryMappedFiles namespace.
It is always possible to use the concept of mapped-memory files by doing some P/Invokes to the underlying
Windows APIs, but now with the introduction of the System.IO.MemoryMappedFiles namespace, you can
work with managed code rather than operating in the cumbersome P/Invoke world.
Mapped-memory files and the use of this namespace are ideal when your application requires frequent or
random access to files. Using this approach allows you to load part or all of the file into a segment of virtual
memory, which then appears to your application as if this file is contained within the primary memory for
the application.
Interestingly, you can use this file in memory as a shared resource among more than one process. Prior
to this, you might have been using Windows Communication Foundation (WCF) or Named Pipes to
communicate a shared resource between multiple processes, but now you can share a mapped-memory file
between processes using a shared name.
To work with mapped-memory files, you have to work with a couple of objects. The first is a
mapped-memory file instance that loads the file. The second is an accessor object. The following code
writes to the mapped-memory file object and then reads from it. You also see that the write is also
happening when the object is disposed:
using System;
using System.IO.MemoryMappedFiles;
using System.Text;
namespace MappedMemoryFiles
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