/// <summary>
/// Removes a session from the dictionary
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="LockCookie">Lock Cookie (used to unlock item if it's locked)</param>
/// <param name="LockedSessionInfo">Locked session information if session is locked</param>
/// <returns>Result of Action</returns>
public SessionActionResult Remove(string Key, uint LockCookie, out SessionResponseInfo LockedSessionInfo)
{
// Look for the 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 Delete again from the start.
// if session is not In Use, Perform Delete
return(Remove(Key, LockCookie, false, DateTime.MinValue, out LockedSessionInfo));
}
/// <summary>
/// Updates or inserts a session in the dictionary
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="Session">Session object</param>
/// <param name="InsertOnly">Indicates that session should only be inserted if it does not already exist</param>
/// <param name="UpdateIfNotFound">Indicates whether session should be updated if the session was not found. If set to flase, this gives the caller a chance to query the network before trying again </param>
/// <param name="LockedSessionInfo">Locked session information if session is locked</param>
/// <returns>Result of Action</returns>
private SessionActionResult UpSert(string Key, ISessionObject Session, bool InsertOnly, bool UpdateIfNotFound, out SessionResponseInfo LockedSessionInfo)
{
// Look for the session using a reader lock.
// If session is not found, switch to a writer lock and insert item.
// If session is found:
// Perform an atomic compare exchange on the variable 'InUse'
// If session is in Use, try Upsert again from the start.
// If session is not in Use, Perform UpSert and reset InUse
// Also update Sorted session list
if (Key == null)
{
throw new ArgumentNullException("Key");
}
if (Session == null)
{
throw new ArgumentNullException("Session");
}
LockedSessionInfo = null;
bool tryAgain;
Diags.ResetDeadLockCounter();
do
{
tryAgain = false;
AcquireReadLock();
ISessionObject entry;
try
{
dict.TryGetValue(Key, out entry);
}
finally
{
ReleaseReadLock();
}
if (entry == null)
{
if (!UpdateIfNotFound)
{
return(SessionActionResult.NotFound);
}
//Session not found -- insert brand new session object
AcquireWriteLock();
try
{
//Check again to be sure now that the write-lock has been obtained
dict.TryGetValue(Key, out entry);
if (entry != null)
{
//ooops -- another thread inserted a seesion with this key while this thread was trying to obtain the write-lock
//so try again
tryAgain = true;
continue;
}
Session.LockCookie = 1; //For some reason Lockcookie starts counting from 2 -- so set it to 1 now so that it increments to 2 when sought
dict[Key] = Session;
expiryList.Add(DateTime.UtcNow.Add(new TimeSpan(0, Session.TimeOut, 0)), Key, Key);
Diags.LogNewSession(Key, Session);
}
finally
{
ReleaseWriteLock();
}
}
else
{
//Session Found
if (InsertOnly)
{
Diags.LogSessionAlreadyExists(Key);
return(SessionActionResult.AlreadyExists); //Do not perform an update if InsertOnly is requested
}
//There is no need to acquire a write lock here since the dictionary is not been modified.
//Only the dictionary entry itself is been updated and such updates are guaranteed to be atomic
//if the atomic InUse property is set.
if (entry.CompareExchangeIsInUse(true, false) == false)
{
//the InUse flag is set, so this code section has exclusive access to this session object
try
{
if (entry.IsLocked)
{
if (!entry.UnLock(Session.LockCookie))
{
//Lockcookie did not match
LockedSessionInfo = (SessionResponseInfo)entry.CreateResponseInfo();
Diags.LogSessionIsLocked(Key);
return(SessionActionResult.Locked);
}
}
Session.LockCookie = entry.LockCookie; //Overwrite the incoming session's lock-cookie with the internal one's so as not to let external input change the lockcookie
Session.ExtraFlags = -1; //disable extra flags since an update is being performed
entry.CopyFrom(Session); //Copy all information from Session to entry
expiryList.Add(DateTime.UtcNow.Add(new TimeSpan(0, Session.TimeOut, 0)), Key, Key); //reset expiry timeout
Diags.LogUpdatedSession(Key, Session);
}
finally
{
entry.CompareExchangeIsInUse(false, true);
}
}
else
{
//Is this entry being exported?
if (entry.IsExporting)
{
//This session is already been exported so leave
Diags.ResetDeadLockCounter();
return(SessionActionResult.Exporting);
}
//Another thread is using this session and will be done soon so try again
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
return(SessionActionResult.OK);
}
/// <summary>
/// Updates a session (adds a new one if it was not found)
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="Session">Session object</param>
/// <param name="UpdateIfNotFound">Indicates whether session should be updated if the session was not found. If set to flase, this gives the caller a chance to query the network before trying again</param>
/// <param name="LockedSessionInfo">Locked session information if session is locked</param>
/// <returns>Result of Action</returns>
public SessionActionResult Update(string Key, ISessionObject Session, bool UpdateIfNotFound, out SessionResponseInfo LockedSessionInfo)
{
//If the item is locked and the new items lockCookie does not match, return SessionActionResult.Locked
//else add the item and return SessionActionResult.OK
//Calls UpSert internally
return(UpSert(Key, Session, false, UpdateIfNotFound, out LockedSessionInfo)); //Insert or Update item
}
/// <summary>
/// Adds a session into the dictionary
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="Session">Session object</param>
/// <param name="UpdateIfNotFound">Indicates whether session should be updated if the session was not found. If set to flase, this gives the caller a chance to query the network before trying again</param>
/// <param name="LockedSessionInfo">Locked session information if session is locked</param>
/// <returns>Result of Action</returns>
public SessionActionResult Add(string Key, ISessionObject Session, bool UpdateIfNotFound, out SessionResponseInfo LockedSessionInfo)
{
//If an item with key already exists, return SessionActionResult.AlreadyExists
//else add the item and return SessionActionResult.OK
//Calls UpSert internally
return(UpSert(Key, Session, true, UpdateIfNotFound, out LockedSessionInfo)); //Insert Item if it doesn't exist
}
/// <summary>
/// Removes a session from the dictionary
/// </summary>
/// <param name="Key">Session Key</param>
/// <param name="LockCookie">Lock Cookie</param>
/// <param name="IsExpiring">Indicates that the item is being removed because it's expiring</param>
/// <param name="ExpiryDate">The Item expiry date (for comparison)</param>
/// <param name="LockedSessionInfo">Locked session information if session is locked</param>
/// <returns>Result of Action</returns>
private SessionActionResult Remove(string Key, uint LockCookie, bool IsExpiring, DateTime ExpiryDate, out SessionResponseInfo LockedSessionInfo)
{
if (Key == null)
{
throw new ArgumentNullException("Key");
}
LockedSessionInfo = null;
bool tryAgain;
Diags.ResetDeadLockCounter();
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)
{
try
{
//The InUse flag is set and so this code section has exclusive access to this session object
AcquireWriteLock();
try
{
//Check again to be sure, now that the write-lock has been obtained
ISessionObject oldEntry = entry;
if (!dict.TryGetValue(Key, out entry))
{
//ooops -- another thread deleted the session from the dictionary while this thread
//was either trying to do the compareExchange (or if buggy, while obtaining the write-lock)
//so try again
oldEntry.CompareExchangeIsInUse(false, true); //unlock the previously locked item
tryAgain = true;
continue;
}
if (IsExpiring)
{
DateTime timeStamp;
if (expiryList.TryGetTimeStamp(Key, out timeStamp))
{
if (timeStamp != ExpiryDate)
{
//The expiration date on this session was updated, so leave
return(SessionActionResult.OK);
}
}
}
if (!IsExpiring && entry.IsLocked) //Locked items DO expire. if not expiring, LockCookie has to match session's
{
if (!entry.UnLock(LockCookie))
{
//Lockcookie did not match
LockedSessionInfo = (SessionResponseInfo)entry.CreateResponseInfo();
Diags.LogSessionIsLocked(Key);
return(SessionActionResult.Locked);
}
}
if (dict.Remove(Key))
{
expiryList.Remove(Key);
if (IsExpiring)
{
Diags.LogSessionExpired(Key);
}
else
{
Diags.LogSessionDeleted(Key);
}
}
else
{
//This should never happen
Diags.Fail("ASSERTION Failed -- Session dictionary was unable to remove key\r\n");
}
}
finally
{
ReleaseWriteLock();
}
}
finally
{
if (entry != null)
{
entry.CompareExchangeIsInUse(false, true);
}
}
}
else
{
//Is this entry being exported?
if (entry.IsExporting)
{
//This session is already been exported so leave
Diags.ResetDeadLockCounter();
return(SessionActionResult.Exporting);
}
//Another thread is using this session and will be done soon so try again
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
return(SessionActionResult.OK);
}
