Data/ProviderBase/DbConnectionFactory.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System.Collections.Generic;
using System.Diagnostics;
using System.Data.Common;
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 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 uint s_pendingOpenNonPooledNext = 0;
        private static Task<DbConnectionInternal>[] s_pendingOpenNonPooled = new Task<DbConnectionInternal>[Environment.ProcessorCount];
        private static Task<DbConnectionInternal> s_completedTask;

        protected DbConnectionFactory()
        {
            _connectionPoolGroups = new Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup>();
            _poolsToRelease = new List<DbConnectionPool>();
            _poolGroupsToRelease = new List<DbConnectionPoolGroup>();
            _pruningTimer = CreatePruningTimer();
        }


        public abstract DbProviderFactory ProviderFactory
        {
            get;
        }


        public void ClearAllPools()
        {
            Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
            foreach (KeyValuePair<DbConnectionPoolKey, DbConnectionPoolGroup> entry in connectionPoolGroups)
            {
                DbConnectionPoolGroup poolGroup = entry.Value;
                if (null != poolGroup)
                {
                    poolGroup.Clear();
                }
            }
        }

        public void ClearPool(DbConnection connection)
        {
            ADP.CheckArgumentNull(connection, nameof(connection));

            DbConnectionPoolGroup poolGroup = GetConnectionPoolGroup(connection);
            if (null != poolGroup)
            {
                poolGroup.Clear();
            }
        }

        public void ClearPool(DbConnectionPoolKey key)
        {
            Debug.Assert(key != null, "key cannot be null");
            ADP.CheckArgumentNull(key.ConnectionString, nameof(key) + "." + nameof(key.ConnectionString));

            DbConnectionPoolGroup poolGroup;
            Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
            if (connectionPoolGroups.TryGetValue(key, out poolGroup))
            {
                poolGroup.Clear();
            }
        }

        internal virtual DbConnectionPoolProviderInfo CreateConnectionPoolProviderInfo(DbConnectionOptions connectionOptions)
        {
            return null;
        }


        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)
            {
                newConnection.MakeNonPooledObject(owningConnection);
            }
            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)
            {
                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);
        }

        protected DbConnectionOptions FindConnectionOptions(DbConnectionPoolKey key)
        {
            Debug.Assert(key != null, "key cannot be null");
            if (!string.IsNullOrEmpty(key.ConnectionString))
            {
                DbConnectionPoolGroup connectionPoolGroup;
                Dictionary<DbConnectionPoolKey, DbConnectionPoolGroup> connectionPoolGroups = _connectionPoolGroups;
                if (connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
                {
                    return connectionPoolGroup.ConnectionOptions;
                }
            }
            return null;
        }

        private static Task<DbConnectionInternal> GetCompletedTask()
        {
            Debug.Assert(Monitor.IsEntered(s_pendingOpenNonPooled), $"Expected {nameof(s_pendingOpenNonPooled)} lock to be held.");
            return s_completedTask ?? (s_completedTask = Task.FromResult<DbConnectionInternal>(null));
        }

        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 postponed 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-robin fashion
                            if (idx == s_pendingOpenNonPooled.Length)
                            {
                                idx = (int)(s_pendingOpenNonPooledNext % s_pendingOpenNonPooled.Length);
                                unchecked
                                {
                                    s_pendingOpenNonPooledNext++;
                                }
                            }

                            // now that we have an antecedent task, schedule our work when it is completed.
                            // If it is a new slot or a completed task, this continuation will start right away.
                            newTask = s_pendingOpenNonPooled[idx].ContinueWith((_) =>
                            {
                                var newConnection = CreateNonPooledConnection(owningConnection, poolGroup, userOptions);
                                if ((oldConnection != null) && (oldConnection.State == ConnectionState.Open))
                                {
                                    oldConnection.PrepareForReplaceConnection();
                                    oldConnection.Dispose();
                                }
                                return newConnection;
                            }, 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))
                                {
                                    // 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);
                }
                else
                {
                    // TODO: move this to src/Common and integrate with SqlClient
                    //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)
                        {
                            // 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 (string.IsNullOrEmpty(key.ConnectionString))
            {
                return (DbConnectionPoolGroup)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;
                }

                // We don't support connection pooling on Win9x
                if (null == poolOptions)
                {
                    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);
                    }
                }


                DbConnectionPoolGroup newConnectionPoolGroup = new DbConnectionPoolGroup(connectionOptions, key, poolOptions);
                newConnectionPoolGroup.ProviderInfo = CreateConnectionPoolGroupProviderInfo(connectionOptions);

                lock (this)
                {
                    connectionPoolGroups = _connectionPoolGroups;
                    if (!connectionPoolGroups.TryGetValue(key, out connectionPoolGroup))
                    {
                        // 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);
                        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;
        }


        private void PruneConnectionPoolGroups(object state)
        {
            // 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);
                            }
                        }
                    }
                }
            }

            // 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);
                            }
                        }
                    }
                }
            }

            // 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
                            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);
            }
        }

        internal void QueuePoolGroupForRelease(DbConnectionPoolGroup poolGroup)
        {
            Debug.Assert(null != poolGroup, "null poolGroup?");

            lock (_poolGroupsToRelease)
            {
                _poolGroupsToRelease.Add(poolGroup);
            }
        }

        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 DbConnectionInternal GetInnerConnection(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);
    }
}