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CSHARP-2423 Fixed Connection Pools lock contention #361

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CSHARP-2423 Fixed Connection Pools lock contention #361

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63 changes: 21 additions & 42 deletions src/MongoDB.Driver.Core/Core/Bindings/CoreServerSessionPool.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using MongoDB.Driver.Core.Clusters;
using MongoDB.Driver.Core.Misc;
Expand All @@ -24,8 +25,7 @@ internal class CoreServerSessionPool : ICoreServerSessionPool
{
// private fields
private readonly ICluster _cluster;
private readonly object _lock = new object();
private readonly List<ICoreServerSession> _pool = new List<ICoreServerSession>();
private readonly ConcurrentQueue<ICoreServerSession> _pool = new ConcurrentQueue<ICoreServerSession>();

// constructors
public CoreServerSessionPool(ICluster cluster)
Expand All @@ -36,24 +36,20 @@ public CoreServerSessionPool(ICluster cluster)
/// <inheritdoc />
public ICoreServerSession AcquireSession()
{
lock (_lock)
// try to find first non-expired session in our FIFO buffer
// if none found - create new session

ICoreServerSession pooledSession;
while (_pool.TryDequeue(out pooledSession))
{
for (var i = _pool.Count - 1; i >= 0; i--)
if (IsAboutToExpire(pooledSession))
{
var pooledSession = _pool[i];
if (IsAboutToExpire(pooledSession))
{
pooledSession.Dispose();
}
else
{
var removeCount = _pool.Count - i; // the one we're about to return and any about to expire ones we skipped over
_pool.RemoveRange(i, removeCount);
return new ReleaseOnDisposeCoreServerSession(pooledSession, this);
}
pooledSession.Dispose();
}
else
{
return new ReleaseOnDisposeCoreServerSession(pooledSession, this);
}

_pool.Clear(); // they're all about to expire
}

return new ReleaseOnDisposeCoreServerSession(new CoreServerSession(), this);
Expand All @@ -62,32 +58,15 @@ public ICoreServerSession AcquireSession()
/// <inheritdoc />
public void ReleaseSession(ICoreServerSession session)
{
lock (_lock)
{
var removeCount = 0;
for (var i = 0; i < _pool.Count; i++)
{
var pooledSession = _pool[i];
if (IsAboutToExpire(pooledSession))
{
pooledSession.Dispose();
removeCount++;
}
else
{
break;
}
}
_pool.RemoveRange(0, removeCount);
// if session is not expired - put it in the FIFO pool

if (IsAboutToExpire(session))
{
session.Dispose();
}
else
{
_pool.Add(session);
}
if (IsAboutToExpire(session))
{
session.Dispose();
}
else
{
_pool.Enqueue(session);
}
}

Expand Down
9 changes: 6 additions & 3 deletions src/MongoDB.Driver.Core/Core/Clusters/Cluster.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -116,10 +116,13 @@ public ClusterDescription Description
{
get
{
lock (_descriptionLock)
{
// we do not need lock here, because reading and writing refs is thread safe
// and the worst thing we can came up with - outdated description,
// but race condition is impossible
//lock (_descriptionLock)
//{
return _description;
}
//}
}
}

Expand Down
68 changes: 31 additions & 37 deletions src/MongoDB.Driver.Core/Core/ConnectionPools/ExclusiveConnectionPool.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Net;
Expand Down Expand Up @@ -712,15 +713,14 @@ public void Dispose()

private class ListConnectionHolder
{
private readonly object _lock = new object();
private readonly List<PooledConnection> _connections;
private readonly ConcurrentQueue<PooledConnection> _connections;

private readonly Action<ConnectionPoolRemovingConnectionEvent> _removingConnectionEventHandler;
private readonly Action<ConnectionPoolRemovedConnectionEvent> _removedConnectionEventHandler;

public ListConnectionHolder(IEventSubscriber eventSubscriber)
{
_connections = new List<PooledConnection>();
_connections = new ConcurrentQueue<PooledConnection>();

eventSubscriber.TryGetEventHandler(out _removingConnectionEventHandler);
eventSubscriber.TryGetEventHandler(out _removedConnectionEventHandler);
Expand All @@ -730,59 +730,56 @@ public int Count
{
get
{
lock (_lock)
{
return _connections.Count;
}
return _connections.Count;
}
}

public void Clear()
{
lock (_lock)
PooledConnection connection;
while (_connections.TryDequeue(out connection))
{
foreach (var connection in _connections)
{
RemoveConnection(connection);
}
_connections.Clear();
RemoveConnection(connection);
}
}

public void Prune()
{
lock (_lock)
// try to clear our FIFO buffer of expired connections
// if first not expired connection is found - it will be returned back to the pool

PooledConnection expired;
while (_connections.TryDequeue(out expired))
{
for (int i = 0; i < _connections.Count; i++)
if (expired.IsExpired)
{
if (_connections[i].IsExpired)
{
RemoveConnection(_connections[i]);
_connections.RemoveAt(i);
break;
}
RemoveConnection(expired);
}
else
{
_connections.Enqueue(expired);
break;
}
}
}

public PooledConnection Acquire()
{
lock (_lock)
// try to find first not expired connection

PooledConnection connection;
while (_connections.TryDequeue(out connection))
{
if (_connections.Count > 0)
if (connection.IsExpired)
{
var connection = _connections[_connections.Count - 1];
_connections.RemoveAt(_connections.Count - 1);
if (connection.IsExpired)
{
RemoveConnection(connection);
}
else
{
return connection;
}
RemoveConnection(connection);
}
else
{
return connection;
}
}

return null;
}

Expand All @@ -794,10 +791,7 @@ public void Return(PooledConnection connection)
return;
}

lock (_lock)
{
_connections.Add(connection);
}
_connections.Enqueue(connection);
}

private void RemoveConnection(PooledConnection connection)
Expand Down