/// <summary>
/// Default constructor.
/// </summary>
public SharedMem()
{
m_hMap = IntPtr.Zero;
m_pvBlock = null;
m_cLock = 0;
m_cbBlock = 0;
m_mutex = null;
}
/// <summary>
/// This method creates a shared memory object with the name passed in pszName
/// and size of cbMem. The method returns <c>true</c> if the memory was created
/// successfully, <c>false</c> if the operation failed for some reason. If the shared
/// memory block is being created for the first time then this method will
/// zero the memory block. If the shared memory block has already been created
/// then this method will link to the existing block. Note that any successfull
/// call to Open() needs to be matched by a call to <see cref="Close" />. This method is
/// threadsafe.
/// </summary>
/// <param name="name">
/// Name of the inbox. This can be a maximum of 128 characters and may
/// not include the backslash (\) character.
/// </param>
/// <param name="cbMem">Size of the memory in bytes.</param>
/// <param name="mode">The opening mode.</param>
public void Open(string name, int cbMem, OpenMode mode)
{
string memName;
string mutexName;
bool fExists;
bool createdNew;
if (name.Length > 128)
{
throw new ArgumentException("Name exceeds 128 characters.", "name");
}
if (name.IndexOfAny(new char[] { '/', '\\' }) != -1)
{
throw new ArgumentException("Name may not include forward or backslashes.");
}
lock (syncLock)
{
Assertion.Test(m_hMap == IntPtr.Zero);
// Here's what the abbreviations mean:
//
// LT = LillTek
// SM = SharedMem
memName = @"Global\LT:SM:" + name;
#if SHAREDMEM_DRIVER
bool fCreated;
m_hMap = WinApi.MEM_Open(memName, cbMem, out fCreated);
fExists = !fCreated;
#else
// Create the memory object
SecurityAttributes sa;
sa = new SecurityAttributes(SecurityAccess.Unrestricted);
try
{
// $hack(jeff.lill):
//
// Beginning with a late service Windows XP service pack, applications not running in
// Windows session 0 as a service cannot create global shared memory or other objects.
// This results in the API below failing by returning a NULL handle and GetLastError()
// returning ERROR_ACCESS_DENIED. Windows added this restriction to prevent malicious
// code from creating global objects that will be used by well known services and then
// squating on them.
//
// The work-around below detects this situation and tries creating a non-global object
// instead. This will work for most unit testing scenarios.
retry:
m_hMap = WinApi.CreateFileMapping(new IntPtr(-1), sa.AttributesPtr, WinApi.PAGE_READWRITE, 0, (uint)cbMem, memName);
if (m_hMap == IntPtr.Zero)
{
int error = WinApi.GetLastError();
if (memName.ToLowerInvariant().StartsWith(@"global\") && error == WinErr.ERROR_ACCESS_DENIED)
{
memName = "LT:SM:" + name;
goto retry;
}
throw new InvalidOperationException(string.Format(null, "Failed on Windows error [{0}].", error));
}
// For some weird reason, Marshal.GetLastWin32Error() is returning ERROR_IO_PENDING
// when CreateFileMapping() is called on an exising block of shared memory instead
// of returning ERROR_ALREADY_EXISTS. So I'm going to call GetLastError() directly.
// This will be a bit of a performance hit but Open() will be called infrequently
// in real applications.
fExists = WinApi.GetLastError() == WinApi.ERROR_ALREADY_EXISTS;
}
finally
{
sa.Close();
}
#endif // SHAREDMEM_DRIVER
m_pvBlock = null;
m_cbBlock = cbMem;
m_cLock = 0;
if (!fExists && mode == OpenMode.OPEN_ONLY)
{
#if SHAREDMEM_DRIVER
WinApi.MEM_Close(m_hMap);
#else
WinApi.CloseHandle(m_hMap);
#endif
m_hMap = IntPtr.Zero;
throw new InvalidOperationException("Shared memory does not exist.");
}
else if (fExists && mode == OpenMode.CREATE_ONLY)
{
#if SHAREDMEM_DRIVER
WinApi.MEM_Close(m_hMap);
#else
WinApi.CloseHandle(m_hMap);
#endif
m_hMap = IntPtr.Zero;
throw new InvalidOperationException("Shared memory already exists.");
}
// Here's what the abbreviations mean:
//
// LT = LillTek
// SM = Shared Memory
// MX = Mutex
mutexName = "LT:SM:MX:" + name;
if (fExists)
{
try
{
// Open the mutex
m_mutex = new GlobalMutex(mutexName);
}
catch
{
#if SHAREDMEM_DRIVER
WinApi.MEM_Close(m_hMap);
#else
WinApi.CloseHandle(m_hMap);
#endif
m_hMap = IntPtr.Zero;
throw;
}
}
else
{
try
{
// Create the mutex
m_mutex = new GlobalMutex(mutexName, true, out createdNew);
if (createdNew)
{
// Map the shared memory and zero it.
byte *p;
p = Lock();
for (int i = 0; i < m_cbBlock; p[i++] = 0)
{
;
}
Unlock();
m_mutex.ReleaseMutex();
}
}
catch
{
#if SHAREDMEM_DRIVER
WinApi.MEM_Close(m_hMap);
#else
WinApi.CloseHandle(m_hMap);
#endif
m_hMap = IntPtr.Zero;
throw;
}
}
}
}