Free-ebooks-library - Bahar Ali Khan

[DllImport ("Kernel32.dll", SetLastError = true)]
static extern bool UnmapViewOfFile (IntPtr map);
[DllImport ("kernel32.dll", SetLastError = true)]
static extern int CloseHandle (IntPtr hObject);
IntPtr fileHandle, fileMap;
public IntPtr Root { get { return fileMap; } }
FileRights dwDesiredAccess,
uint dwFileOffsetHigh,
uint dwFileOffsetLow,
uint dwNumberOfBytesToMap);
public SharedMem (string name, bool existing, uint sizeInBytes)
{
if (existing)
fileHandle = OpenFileMapping (FileRights.ReadWrite, false, name);
else
fileHandle = CreateFileMapping (NoFileHandle, 0,
FileProtection.ReadWrite,
0, sizeInBytes, name);
if (fileHandle == IntPtr.Zero)
throw new Win32Exception();
}
// Obtain a read/write map for the entire file
fileMap = MapViewOfFile (fileHandle, FileRights.ReadWrite, 0, 0, 0);
if (fileMap == IntPtr.Zero)
throw new Win32Exception();
public void Dispose()
{
if (fileMap != IntPtr.Zero) UnmapViewOfFile (fileMap);
if (fileHandle != IntPtr.Zero) CloseHandle (fileHandle);
fileMap = fileHandle = IntPtr.Zero;
}
}
In this example, we set SetLastError=true on the DllImport methods that use the
SetLastError protocol for emitting error codes. This ensures that the Win32Excep
tion is populated with details of the error when that exception is thrown. (It also
allows you to query the error explicitly by calling Marshal.GetLastWin32Error.)
In order to demonstrate this class, we need to run two applications. The first one
creates the shared memory, as follows:
using (SharedMem sm = new SharedMem ("MyShare", false, 1000))
{
IntPtr root = sm.Root;
// I have shared memory!
Console.ReadLine(); // Here's where we start a second app...
}
964 | Chapter 25: Native and COM Interoperability