/********************************************************
* ADO.NET 2.0 Data Provider for SQLite Version 3.X
* Written by Robert Simpson (robert@blackcastlesoft.com)
*
* Released to the public domain, use at your own risk!
********************************************************/
namespace System.Data.SQLite
{
using System;
using System.Collections.Generic;
internal static class SQLiteConnectionPool
{
/// <summary>
/// Keeps track of connections made on a specified file. The PoolVersion dictates whether old objects get
/// returned to the pool or discarded when no longer in use.
/// </summary>
internal class Pool
{
internal readonly Queue<WeakReference> Queue = new Queue<WeakReference>();
internal int PoolVersion;
internal int MaxPoolSize;
internal Pool(int version, int maxSize)
{
PoolVersion = version;
MaxPoolSize = maxSize;
}
}
/// <summary>
/// The connection pool object
/// </summary>
private static SortedList<string, Pool> _connections = new SortedList<string, Pool>(StringComparer.OrdinalIgnoreCase);
/// <summary>
/// The default version number new pools will get
/// </summary>
private static int _poolVersion = 1;
/// <summary>
/// Attempt to pull a pooled connection out of the queue for active duty
/// </summary>
/// <param name="fileName">The filename for a desired connection</param>
/// <param name="maxPoolSize">The maximum size the connection pool for the filename can be</param>
/// <param name="version">The pool version the returned connection will belong to</param>
/// <returns>Returns NULL if no connections were available. Even if none are, the poolversion will still be a valid pool version</returns>
internal static SQLiteConnectionHandle Remove(string fileName, int maxPoolSize, out int version)
{
lock (_connections)
{
Pool queue;
// Default to the highest pool version
version = _poolVersion;
// If we didn't find a pool for this file, create one even though it will be empty.
// We have to do this here because otherwise calling ClearPool() on the file will not work for active connections
// that have never seen the pool yet.
if (_connections.TryGetValue(fileName, out queue) == false)
{
queue = new Pool(_poolVersion, maxPoolSize);
_connections.Add(fileName, queue);
return null;
}
// We found a pool for this file, so use its version number
version = queue.PoolVersion;
queue.MaxPoolSize = maxPoolSize;
ResizePool(queue, false);
// Try and get a pooled connection from the queue
while (queue.Queue.Count > 0)
{
WeakReference cnn = queue.Queue.Dequeue();
SQLiteConnectionHandle hdl = cnn.Target as SQLiteConnectionHandle;
if (hdl != null)
{
return hdl;
}
}
return null;
}
}
/// <summary>
/// Clears out all pooled connections and rev's up the default pool version to force all old active objects
/// not in the pool to get discarded rather than returned to their pools.
/// </summary>
internal static void ClearAllPools()
{
lock (_connections)
{
foreach (KeyValuePair<string, Pool> pair in _connections)
{
while (pair.Value.Queue.Count > 0)
{
WeakReference cnn = pair.Value.Queue.Dequeue();
SQLiteConnectionHandle hdl = cnn.Target as SQLiteConnectionHandle;
if (hdl != null)
{
hdl.Dispose();
}
}
// Keep track of the highest revision so we can go one higher when we're finished
if (_poolVersion <= pair.Value.PoolVersion)
_poolVersion = pair.Value.PoolVersion + 1;
}
// All pools are cleared and we have a new highest version number to force all old version active items to get discarded
// instead of going back to the queue when they are closed.
// We can get away with this because we're pumped up the _poolVersion out of range of all active connections, so they
// will all get discarded when they try to put themselves back in their pool.
_connections.Clear();
}
}
/// <summary>
/// Clear a given pool for a given filename. Discards anything in the pool for the given file, and revs the pool
/// version so current active objects on the old version of the pool will get discarded rather than be returned to the pool.
/// </summary>
/// <param name="fileName">The filename of the pool to clear</param>
internal static void ClearPool(string fileName)
{
lock (_connections)
{
Pool queue;
if (_connections.TryGetValue(fileName, out queue) == true)
{
queue.PoolVersion++;
while (queue.Queue.Count > 0)
{
WeakReference cnn = queue.Queue.Dequeue();
SQLiteConnectionHandle hdl = cnn.Target as SQLiteConnectionHandle;
if (hdl != null)
{
hdl.Dispose();
}
}
}
}
}
/// <summary>
/// Return a connection to the pool for someone else to use.
/// </summary>
/// <param name="fileName">The filename of the pool to use</param>
/// <param name="hdl">The connection handle to pool</param>
/// <param name="version">The pool version the handle was created under</param>
/// <remarks>
/// If the version numbers don't match between the connection and the pool, then the handle is discarded.
/// </remarks>
internal static void Add(string fileName, SQLiteConnectionHandle hdl, int version)
{
lock (_connections)
{
// If the queue doesn't exist in the pool, then it must've been cleared sometime after the connection was created.
Pool queue;
if (_connections.TryGetValue(fileName, out queue) == true && version == queue.PoolVersion)
{
ResizePool(queue, true);
queue.Queue.Enqueue(new WeakReference(hdl, false));
GC.KeepAlive(hdl);
}
else
{
hdl.Close();
}
}
}
private static void ResizePool(Pool queue, bool forAdding)
{
int target = queue.MaxPoolSize;
if (forAdding && target > 0) target--;
while (queue.Queue.Count > target)
{
WeakReference cnn = queue.Queue.Dequeue();
SQLiteConnectionHandle hdl = cnn.Target as SQLiteConnectionHandle;
if (hdl != null)
{
hdl.Dispose();
}
}
}
}
}