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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Data.Common;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
namespace System.Data.ProviderBase
{
internal abstract class DbConnectionFactory
{
private Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> _connectionPoolGroups;
private readonly List<DbConnectionPool> _poolsToRelease;
private readonly List<DbConnectionPoolGroup> _poolGroupsToRelease;
private readonly DbConnectionPoolCounters _performanceCounters;
private readonly Timer _pruningTimer;
private const int PruningDueTime = 4 * 60 * 1000; // 4 minutes
private const int PruningPeriod = 30 * 1000; // thirty seconds
// s_pendingOpenNonPooled is an array of tasks used to throttle creation of non-pooled connections to
// a maximum of Environment.ProcessorCount at a time.
private static int s_pendingOpenNonPooledNext;
private static readonly Task<DbConnectionInternal?>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal?>[Environment.ProcessorCount];
private static Task<DbConnectionInternal?>? s_completedTask;
protected DbConnectionFactory() : this(DbConnectionPoolCountersNoCounters.SingletonInstance) { }
protected DbConnectionFactory(DbConnectionPoolCounters performanceCounters)
{
_performanceCounters = performanceCounters;
_connectionPoolGroups = new Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup>();
_poolsToRelease = new List<DbConnectionPool>();
_poolGroupsToRelease = new List<DbConnectionPoolGroup>();
_pruningTimer = CreatePruningTimer();
}
internal DbConnectionPoolCounters PerformanceCounters
{
get { return _performanceCounters; }
}
public abstract DbProviderFactory ProviderFactory
{
get;
}
public void ClearAllPools()
{
Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
foreach (KeyValuePair<DbConnectionPoolKey, DbConnectionPoolGroup> entry in connectionPoolGroups)
{
entry.Value?.Clear();
}
}
protected virtual DbMetaDataFactory CreateMetaDataFactory(DbConnectionInternal internalConnection, out bool cacheMetaDataFactory)
{
// providers that support GetSchema must override this with a method that creates a meta data
// factory appropriate for them.
cacheMetaDataFactory = false;
throw ADP.NotSupported();
}
internal DbConnectionInternal? CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup, DbConnectionOptions? userOptions)
{
Debug.Assert(null != owningConnection, "null owningConnection?");
Debug.Assert(null != poolGroup, "null poolGroup?");
DbConnectionOptions connectionOptions = poolGroup.ConnectionOptions;
DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = poolGroup.ProviderInfo!;
DbConnectionPoolKey poolKey = poolGroup.PoolKey;
DbConnectionInternal newConnection = CreateConnection(connectionOptions, poolKey, poolGroupProviderInfo, null, owningConnection, userOptions);
if (null != newConnection)
{
PerformanceCounters.HardConnectsPerSecond.Increment();
newConnection.MakeNonPooledObject(owningConnection, PerformanceCounters);
}
return newConnection;
}
internal DbConnectionInternal? CreatePooledConnection(DbConnectionPool pool, DbConnection? owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions? userOptions)
{
Debug.Assert(null != pool, "null pool?");
DbConnectionPoolGroupProviderInfo poolGroupProviderInfo = pool.PoolGroup.ProviderInfo!;
DbConnectionInternal newConnection = CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningObject, userOptions);
if (null != newConnection)
{
PerformanceCounters.HardConnectsPerSecond.Increment();
newConnection.MakePooledConnection(pool);
}
return newConnection;
}
internal virtual DbConnectionPoolGroupProviderInfo? CreateConnectionPoolGroupProviderInfo(DbConnectionOptions connectionOptions)
{
return null;
}
private Timer CreatePruningTimer()
{
TimerCallback callback = new TimerCallback(PruneConnectionPoolGroups);
return new Timer(callback, null, PruningDueTime, PruningPeriod);
}
// GetCompletedTask must be called from within s_pendingOpenPooled lock
private static Task<DbConnectionInternal?> GetCompletedTask()
{
if (s_completedTask == null)
{
TaskCompletionSource<DbConnectionInternal?> source = new TaskCompletionSource<DbConnectionInternal?>();
source.SetResult(null);
s_completedTask = source.Task;
}
return s_completedTask;
}
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;
// 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.
// 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((_) =>
{
Transactions.Transaction? originalTransaction = ADP.GetCurrentTransaction();
try
{
ADP.SetCurrentTransaction(retry.Task.AsyncState as 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 (!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)
{
// 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.
Threading.Thread.Sleep(timeBetweenRetriesMilliseconds);
timeBetweenRetriesMilliseconds *= 2; // double the wait time for next iteration
}
}
}
} while (connection == null && retriesLeft-- > 0);
if (connection == null)
{
// exhausted all retries or timed out - give up
throw ADP.PooledOpenTimeout();
}
return true;
}
private DbConnectionPool? GetConnectionPool(DbConnection owningObject, DbConnectionPoolGroup connectionPoolGroup)
{
// if poolgroup is disabled, it will be replaced with a new entry
Debug.Assert(null != owningObject, "null owningObject?");
Debug.Assert(null != connectionPoolGroup, "null connectionPoolGroup?");
// It is possible that while the outer connection object has
// been sitting around in a closed and unused state in some long
// running app, the pruner may have come along and remove this
// the pool entry from the master list. If we were to use a
// pool entry in this state, we would create "unmanaged" pools,
// which would be bad. To avoid this problem, we automagically
// re-create the pool entry whenever it's disabled.
// however, don't rebuild connectionOptions if no pooling is involved - let new connections do that work
if (connectionPoolGroup.IsDisabled && (null != connectionPoolGroup.PoolGroupOptions))
{
// reusing existing pool option in case user originally used SetConnectionPoolOptions
DbConnectionPoolGroupOptions poolOptions = connectionPoolGroup.PoolGroupOptions;
// get the string to hash on again
DbConnectionOptions? connectionOptions = connectionPoolGroup.ConnectionOptions;
Debug.Assert(null != connectionOptions, "prevent expansion of connectionString");
connectionPoolGroup = GetConnectionPoolGroup(connectionPoolGroup.PoolKey, poolOptions, ref connectionOptions)!;
Debug.Assert(null != connectionPoolGroup, "null connectionPoolGroup?");
SetConnectionPoolGroup(owningObject, connectionPoolGroup);
}
DbConnectionPool? connectionPool = connectionPoolGroup.GetConnectionPool(this);
return connectionPool;
}
internal DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnectionPoolKey key, DbConnectionPoolGroupOptions? poolOptions, ref DbConnectionOptions? userConnectionOptions)
{
if (ADP.IsEmpty(key.ConnectionString))
{
return null;
}
DbConnectionPoolGroup? connectionPoolGroup;
Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup) || (connectionPoolGroup.IsDisabled && (null != connectionPoolGroup.PoolGroupOptions)))
{
// If we can't find an entry for the connection string in
// our collection of pool entries, then we need to create a
// new pool entry and add it to our collection.
DbConnectionOptions connectionOptions = CreateConnectionOptions(key.ConnectionString, userConnectionOptions);
if (null == connectionOptions)
{
throw ADP.InternalConnectionError(ADP.ConnectionError.ConnectionOptionsMissing);
}
if (null == userConnectionOptions)
{ // we only allow one expansion on the connection string
userConnectionOptions = connectionOptions;
string expandedConnectionString = connectionOptions.Expand();
// if the expanded string is same instance (default implementation), the use the already created options
if ((object)expandedConnectionString != (object)key.ConnectionString)
{
// CONSIDER: caching the original string to reduce future parsing
DbConnectionPoolKey newKey = (DbConnectionPoolKey)((ICloneable)key).Clone();
newKey.ConnectionString = expandedConnectionString;
return GetConnectionPoolGroup(newKey, null, ref userConnectionOptions);
}
}
// We don't support connection pooling on Win9x; it lacks too many of the APIs we require.
if ((null == poolOptions) && ADP.IsWindowsNT)
{
if (null != connectionPoolGroup)
{
// reusing existing pool option in case user originally used SetConnectionPoolOptions
poolOptions = connectionPoolGroup.PoolGroupOptions;
}
else
{
// Note: may return null for non-pooled connections
poolOptions = CreateConnectionPoolGroupOptions(connectionOptions);
}
}
lock (this)
{
connectionPoolGroups = _connectionPoolGroups;
if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
{
DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions!);
newConnectionPoolGroup.ProviderInfo = CreateConnectionPoolGroupProviderInfo(connectionOptions);
// build new dictionary with space for new connection string
Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> newConnectionPoolGroups = new Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup>(1 + connectionPoolGroups.Count);
foreach (KeyValuePair<DbConnectionPoolKey, DbConnectionPoolGroup> entry in connectionPoolGroups)
{
newConnectionPoolGroups.Add(entry.Key, entry.Value);
}
// lock prevents race condition with PruneConnectionPoolGroups
newConnectionPoolGroups.Add(key, newConnectionPoolGroup);
PerformanceCounters.NumberOfActiveConnectionPoolGroups.Increment();
connectionPoolGroup = newConnectionPoolGroup;
_connectionPoolGroups = newConnectionPoolGroups;
}
else
{
Debug.Assert(!connectionPoolGroup.IsDisabled, "Disabled pool entry discovered");
}
}
Debug.Assert(null != connectionPoolGroup, "how did we not create a pool entry?");
Debug.Assert(null != userConnectionOptions, "how did we not have user connection options?");
}
else if (null == userConnectionOptions)
{
userConnectionOptions = connectionPoolGroup.ConnectionOptions;
}
return connectionPoolGroup;
}
internal DbMetaDataFactory GetMetaDataFactory(DbConnectionPoolGroup connectionPoolGroup, DbConnectionInternal internalConnection)
{
Debug.Assert(connectionPoolGroup != null, "connectionPoolGroup may not be null.");
// get the matadatafactory from the pool entry. If it does not already have one
// create one and save it on the pool entry
DbMetaDataFactory? metaDataFactory = connectionPoolGroup.MetaDataFactory;
// consider serializing this so we don't construct multiple metadata factories
// if two threads happen to hit this at the same time. One will be GC'd
if (metaDataFactory == null)
{
metaDataFactory = CreateMetaDataFactory(internalConnection, out bool allowCache);
if (allowCache)
{
connectionPoolGroup.MetaDataFactory = metaDataFactory;
}
}
return metaDataFactory;
}
private void PruneConnectionPoolGroups(object? state)
{
// when debugging this method, expect multiple threads at the same time
// First, walk the pool release list and attempt to clear each
// pool, when the pool is finally empty, we dispose of it. If the
// pool isn't empty, it's because there are active connections or
// distributed transactions that need it.
lock (_poolsToRelease)
{
if (0 != _poolsToRelease.Count)
{
DbConnectionPool[] poolsToRelease = _poolsToRelease.ToArray();
foreach (DbConnectionPool pool in poolsToRelease)
{
if (null != pool)
{
pool.Clear();
if (0 == pool.Count)
{
_poolsToRelease.Remove(pool);
PerformanceCounters.NumberOfInactiveConnectionPools.Decrement();
}
}
}
}
}
// Next, walk the pool entry release list and dispose of each
// pool entry when it is finally empty. If the pool entry isn't
// empty, it's because there are active pools that need it.
lock (_poolGroupsToRelease)
{
if (0 != _poolGroupsToRelease.Count)
{
DbConnectionPoolGroup[] poolGroupsToRelease = _poolGroupsToRelease.ToArray();
foreach (DbConnectionPoolGroup poolGroup in poolGroupsToRelease)
{
if (null != poolGroup)
{
int poolsLeft = poolGroup.Clear(); // may add entries to _poolsToRelease
if (0 == poolsLeft)
{
_poolGroupsToRelease.Remove(poolGroup);
PerformanceCounters.NumberOfInactiveConnectionPoolGroups.Decrement();
}
}
}
}
}
// Finally, we walk through the collection of connection pool entries
// and prune each one. This will cause any empty pools to be put
// into the release list.
lock (this)
{
Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> newConnectionPoolGroups = new Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup>(connectionPoolGroups.Count);
foreach (KeyValuePair<DbConnectionPoolKey, DbConnectionPoolGroup> entry in connectionPoolGroups)
{
if (null != entry.Value)
{
Debug.Assert(!entry.Value.IsDisabled, "Disabled pool entry discovered");
// entries start active and go idle during prune if all pools are gone
// move idle entries from last prune pass to a queue for pending release
// otherwise process entry which may move it from active to idle
if (entry.Value.Prune())
{ // may add entries to _poolsToRelease
PerformanceCounters.NumberOfActiveConnectionPoolGroups.Decrement();
QueuePoolGroupForRelease(entry.Value);
}
else
{
newConnectionPoolGroups.Add(entry.Key, entry.Value);
}
}
}
_connectionPoolGroups = newConnectionPoolGroups;
}
}
internal void QueuePoolForRelease(DbConnectionPool pool, bool clearing)
{
// Queue the pool up for release -- we'll clear it out and dispose
// of it as the last part of the pruning timer callback so we don't
// do it with the pool entry or the pool collection locked.
Debug.Assert(null != pool, "null pool?");
// set the pool to the shutdown state to force all active
// connections to be automatically disposed when they
// are returned to the pool
pool.Shutdown();
lock (_poolsToRelease)
{
if (clearing)
{
pool.Clear();
}
_poolsToRelease.Add(pool);
}
PerformanceCounters.NumberOfInactiveConnectionPools.Increment();
}
internal void QueuePoolGroupForRelease(DbConnectionPoolGroup poolGroup)
{
Debug.Assert(null != poolGroup, "null poolGroup?");
lock (_poolGroupsToRelease)
{
_poolGroupsToRelease.Add(poolGroup);
}
PerformanceCounters.NumberOfInactiveConnectionPoolGroups.Increment();
}
protected virtual DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection, DbConnectionOptions? userOptions)
{
return CreateConnection(options, poolKey, poolGroupProviderInfo, pool, owningConnection);
}
protected abstract DbConnectionInternal CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, object poolGroupProviderInfo, DbConnectionPool? pool, DbConnection? owningConnection);
protected abstract DbConnectionOptions CreateConnectionOptions(string connectionString, DbConnectionOptions? previous);
protected abstract DbConnectionPoolGroupOptions? CreateConnectionPoolGroupOptions(DbConnectionOptions options);
internal abstract DbConnectionPoolGroup? GetConnectionPoolGroup(DbConnection connection);
internal abstract void PermissionDemand(DbConnection outerConnection);
internal abstract void SetConnectionPoolGroup(DbConnection outerConnection, DbConnectionPoolGroup poolGroup);
internal abstract void SetInnerConnectionEvent(DbConnection owningObject, DbConnectionInternal to);
internal abstract bool SetInnerConnectionFrom(DbConnection owningObject, DbConnectionInternal to, DbConnectionInternal from);
internal abstract void SetInnerConnectionTo(DbConnection owningObject, DbConnectionInternal to);
}
}
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