/// <summary>
/// Begins an external session export
/// </summary>
/// <param name="Key">Session key</param>
/// <param name="Reader">Method to call to kickstart export</param>
/// <param name="StateObject">State object</param>
/// <returns>Result of the operation</returns>
public SessionActionResult BeginExport(string Key, SessionReadHandler Reader, object StateObject)
{
// Look for session using a reader lock.
// If session is not found, return not found;
// If session is found:
// Perform an atomic compare exchange on the variable 'InUse'
// if session is in Use, try read again from the start.
// if session is not in use, call delegate and return OK response -- do not reset inuse property
return(Read(Key, Reader, StateObject, true));
}
/// <summary>
/// Reads a stored session
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="Reader">Method to call to complete read</param>
/// <param name="StateObject">State object</param>
/// <returns>Result of read action</returns>
public SessionActionResult Read(string Key, SessionReadHandler Reader, object StateObject)
{
// Look for session using a reader lock.
// If session is not found, return false;
// If session is found:
// Perform an atomic compare exchange on the variable 'InUse'
// if session is in Use, try read again from the start.
// if session is not in use, call delegate and return OK
return(Read(Key, Reader, StateObject, false));
}
/// <summary>
/// Reads a stored session
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="Reader">Method to call to complete read</param>
/// <param name="StateObject">State object</param>
/// <param name="isExporting">Indicates if the session is to be exported</param>
/// <returns>Result of read action</returns>
private SessionActionResult Read(string Key, SessionReadHandler Reader, object StateObject, bool isExporting)
{
if (Key == null)
{
throw new ArgumentNullException("Key");
}
bool tryAgain;
bool sessionIslocked = false;
Diags.ResetDeadLockCounter(); //Reset Dead lock counter
do
{
tryAgain = false;
AcquireReadLock();
ISessionObject entry;
try
{
dict.TryGetValue(Key, out entry);
}
finally
{
ReleaseReadLock();
}
if (entry == null)
{
//Session not found
Diags.LogSessionNotFound(Key);
return(SessionActionResult.NotFound);
}
else
{
//Session Found
if (entry.CompareExchangeIsInUse(true, false) == false)
{
//The InUse flag has been set and now this thread has exclusive access to this session object
try
{
//Set IsExporting flag for this entry if item is to be exported
if (isExporting)
{
entry.IsExporting = true;
}
//Call Reader Delegate
if (Reader != null)
{
Reader(entry, StateObject);
}
if (isExporting)
{
Diags.LogSessionExporting(Key, entry);
}
else
{
Diags.LogSessionRead(Key, entry);
}
sessionIslocked = entry.IsLocked;
}
finally
{
if (!isExporting) //Remove inUse property if not exporting
{
entry.CompareExchangeIsInUse(false, true);
}
}
}
else
{
//Nope, it's still there so check if it's been exported and try again
if (entry.IsExporting)
{
//This session is already been exported so leave
Diags.ResetDeadLockCounter();
return(SessionActionResult.Exporting);
}
Thread.Sleep(1); //pause for 1 ms
tryAgain = true;
}
Diags.DetectDeadLock(Key, DeadLockIterationCount); //Signal a deadlock after 2000 iterations
}
} while (tryAgain);
Diags.ResetDeadLockCounter(); //Signal deadlock was freed
if (sessionIslocked && !isExporting)
{
Diags.LogSessionIsLocked(Key);
return(SessionActionResult.Locked);
}
else
{
return(SessionActionResult.OK);
}
}
