private Task <DbConnectionInternal> CreateReplaceConnectionContinuation(Task <DbConnectionInternal> task, DbConnection owningConnection, TaskCompletionSource <DbConnectionInternal> retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionPoolGroup poolGroup, CancellationTokenSource cancellationTokenSource)
{
return(task.ContinueWith(
(_) =>
{
Transaction originalTransaction = ADP.GetCurrentTransaction();
try
{
ADP.SetCurrentTransaction(retry.Task.AsyncState as Transaction);
var newConnection = CreateNonPooledConnection(owningConnection, poolGroup, userOptions);
if ((oldConnection != null) && (oldConnection.State == ConnectionState.Open))
{
oldConnection.PrepareForReplaceConnection();
oldConnection.Dispose();
}
return newConnection;
}
finally
{
ADP.SetCurrentTransaction(originalTransaction);
}
},
cancellationTokenSource.Token,
TaskContinuationOptions.LongRunning,
TaskScheduler.Default
));
}
internal bool TryGetConnection(DbConnection owningConnection, TaskCompletionSource <DbConnectionInternal> retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, out DbConnectionInternal connection)
{
Debug.Assert(null != owningConnection, "null owningConnection?");
DbConnectionPoolGroup poolGroup;
DbConnectionPool connectionPool;
connection = null;
// SQLBU 431251:
// Work around race condition with clearing the pool between GetConnectionPool obtaining pool
// and GetConnection on the pool checking the pool state. Clearing the pool in this window
// will switch the pool into the ShuttingDown state, and GetConnection will return null.
// There is probably a better solution involving locking the pool/group, but that entails a major
// re-design of the connection pooling synchronization, so is post-poned for now.
// VSDD 674236: use retriesLeft to prevent CPU spikes with incremental sleep
// start with one msec, double the time every retry
// max time is: 1 + 2 + 4 + ... + 2^(retries-1) == 2^retries -1 == 1023ms (for 10 retries)
int retriesLeft = 10;
int timeBetweenRetriesMilliseconds = 1;
do
{
poolGroup = GetConnectionPoolGroup(owningConnection);
// Doing this on the callers thread is important because it looks up the WindowsIdentity from the thread.
connectionPool = GetConnectionPool(owningConnection, poolGroup);
if (null == connectionPool)
{
// If GetConnectionPool returns null, we can be certain that
// this connection should not be pooled via DbConnectionPool
// or have a disabled pool entry.
poolGroup = GetConnectionPoolGroup(owningConnection); // previous entry have been disabled
if (retry != null)
{
Task <DbConnectionInternal> newTask;
CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
lock (s_pendingOpenNonPooled)
{
// look for an available task slot (completed or empty)
int idx;
for (idx = 0; idx < s_pendingOpenNonPooled.Length; idx++)
{
Task task = s_pendingOpenNonPooled[idx];
if (task == null)
{
s_pendingOpenNonPooled[idx] = GetCompletedTask();
break;
}
else if (task.IsCompleted)
{
break;
}
}
// if didn't find one, pick the next one in round-robbin fashion
if (idx == s_pendingOpenNonPooled.Length)
{
idx = s_pendingOpenNonPooledNext++ % s_pendingOpenNonPooled.Length;
}
// now that we have an antecedent task, schedule our work when it is completed.
// If it is a new slot or a compelted task, this continuation will start right away.
// BUG? : If we have timed out task on top of running task, then new task could be started
// on top of that, since we are only checking the top task. This will lead to starting more threads
// than intended.
newTask = s_pendingOpenNonPooled[idx].ContinueWith((_) =>
{
System.Transactions.Transaction originalTransaction = ADP.GetCurrentTransaction();
try
{
ADP.SetCurrentTransaction(retry.Task.AsyncState as System.Transactions.Transaction);
var newConnection = CreateNonPooledConnection(owningConnection, poolGroup, userOptions);
if ((oldConnection != null) && (oldConnection.State == ConnectionState.Open))
{
oldConnection.PrepareForReplaceConnection();
oldConnection.Dispose();
}
return(newConnection);
}
finally
{
ADP.SetCurrentTransaction(originalTransaction);
}
}, cancellationTokenSource.Token, TaskContinuationOptions.LongRunning, TaskScheduler.Default);
// Place this new task in the slot so any future work will be queued behind it
s_pendingOpenNonPooled[idx] = newTask;
}
// Set up the timeout (if needed)
if (owningConnection.ConnectionTimeout > 0)
{
int connectionTimeoutMilliseconds = owningConnection.ConnectionTimeout * 1000;
cancellationTokenSource.CancelAfter(connectionTimeoutMilliseconds);
}
// once the task is done, propagate the final results to the original caller
newTask.ContinueWith((task) =>
{
cancellationTokenSource.Dispose();
if (task.IsCanceled)
{
retry.TrySetException(ADP.ExceptionWithStackTrace(ADP.NonPooledOpenTimeout()));
}
else if (task.IsFaulted)
{
retry.TrySetException(task.Exception.InnerException);
}
else
{
if (retry.TrySetResult(task.Result))
{
PerformanceCounters.NumberOfNonPooledConnections.Increment();
}
else
{
// The outer TaskCompletionSource was already completed
// Which means that we don't know if someone has messed with the outer connection in the middle of creation
// So the best thing to do now is to destroy the newly created connection
task.Result.DoomThisConnection();
task.Result.Dispose();
}
}
}, TaskScheduler.Default);
return(false);
}
connection = CreateNonPooledConnection(owningConnection, poolGroup, userOptions);
PerformanceCounters.NumberOfNonPooledConnections.Increment();
}
else
{
if (((SqlClient.SqlConnection)owningConnection).ForceNewConnection)
{
Debug.Assert(!(oldConnection is DbConnectionClosed), "Force new connection, but there is no old connection");
connection = connectionPool.ReplaceConnection(owningConnection, userOptions, oldConnection);
}
else
{
if (!connectionPool.TryGetConnection(owningConnection, retry, userOptions, out connection))
{
return(false);
}
}
if (connection == null)
{
// connection creation failed on semaphore waiting or if max pool reached
if (connectionPool.IsRunning)
{
SqlClientEventSource.Log.TraceEvent("<prov.DbConnectionFactory.GetConnection|RES|CPOOL> {0}, GetConnection failed because a pool timeout occurred.", ObjectID);
// If GetConnection failed while the pool is running, the pool timeout occurred.
throw ADP.PooledOpenTimeout();
}
else
{
// We've hit the race condition, where the pool was shut down after we got it from the group.
// Yield time slice to allow shut down activities to complete and a new, running pool to be instantiated
// before retrying.
System.Threading.Thread.Sleep(timeBetweenRetriesMilliseconds);
timeBetweenRetriesMilliseconds *= 2; // double the wait time for next iteration
}
}
}
} while (connection == null && retriesLeft-- > 0);
if (connection == null)
{
SqlClientEventSource.Log.TraceEvent("<prov.DbConnectionFactory.GetConnection|RES|CPOOL> {0}, GetConnection failed because a pool timeout occurred and all retries were exhausted.", ObjectID);
// exhausted all retries or timed out - give up
throw ADP.PooledOpenTimeout();
}
return(true);
}