Github user jorgebay commented on a diff in the pull request:
https://github.com/apache/tinkerpop/pull/903#discussion_r209870927
--- Diff: gremlin-dotnet/src/Gremlin.Net/Driver/ConnectionPool.cs ---
@@ -33,91 +34,134 @@ internal class ConnectionPool : IDisposable
{
private readonly ConnectionFactory _connectionFactory;
private readonly ConcurrentBag<Connection> _connections = new
ConcurrentBag<Connection>();
- private readonly object _connectionsLock = new object();
+ private readonly AutoResetEvent _newConnectionAvailable = new
AutoResetEvent(false);
+ private readonly int _minPoolSize;
+ private readonly int _maxPoolSize;
+ private readonly TimeSpan _waitForConnectionTimeout;
+ private int _nrConnections;
- public ConnectionPool(ConnectionFactory connectionFactory)
+ public ConnectionPool(ConnectionFactory connectionFactory,
ConnectionPoolSettings settings)
{
_connectionFactory = connectionFactory;
+ _minPoolSize = settings.MinSize;
+ _maxPoolSize = settings.MaxSize;
+ _waitForConnectionTimeout = settings.WaitForConnectionTimeout;
+ PopulatePoolAsync().WaitUnwrap();
}
- public int NrConnections { get; private set; }
+ public int NrConnections => Interlocked.CompareExchange(ref
_nrConnections, 0, 0);
+
+ private async Task PopulatePoolAsync()
+ {
+ var connectionCreationTasks = new
List<Task<Connection>>(_minPoolSize);
+ for (var i = 0; i < _minPoolSize; i++)
+ {
+ connectionCreationTasks.Add(CreateNewConnectionAsync());
+ }
+
+ var createdConnections = await
Task.WhenAll(connectionCreationTasks).ConfigureAwait(false);
+ foreach (var c in createdConnections)
+ {
+ _connections.Add(c);
+ }
+
+ Interlocked.CompareExchange(ref _nrConnections, _minPoolSize,
0);
+ }
public async Task<IConnection> GetAvailableConnectionAsync()
{
- if (!TryGetConnectionFromPool(out var connection))
- connection = await
CreateNewConnectionAsync().ConfigureAwait(false);
+ if (TryGetConnectionFromPool(out var connection))
+ return ProxiedConnection(connection);
+ connection = await
AddConnectionIfUnderMaximumAsync().ConfigureAwait(false) ?? WaitForConnection();
+ return ProxiedConnection(connection);
+ }
- return new ProxyConnection(connection, AddConnectionIfOpen);
+ private IConnection ProxiedConnection(Connection connection)
+ {
+ return new ProxyConnection(connection, ReturnConnectionIfOpen);
}
- private bool TryGetConnectionFromPool(out Connection connection)
+ private void ReturnConnectionIfOpen(Connection connection)
+ {
+ if (!connection.IsOpen)
+ {
+ ConsiderUnavailable();
+ DefinitelyDestroyConnection(connection);
+ return;
+ }
+
+ _connections.Add(connection);
+ _newConnectionAvailable.Set();
+ }
+
+ private async Task<Connection> AddConnectionIfUnderMaximumAsync()
{
while (true)
{
- connection = null;
- lock (_connectionsLock)
- {
- if (_connections.IsEmpty) return false;
- _connections.TryTake(out connection);
- }
+ var nrOpened = Interlocked.CompareExchange(ref
_nrConnections, 0, 0);
+ if (nrOpened >= _maxPoolSize) return null;
- if (connection.IsOpen) return true;
- connection.Dispose();
+ if (Interlocked.CompareExchange(ref _nrConnections,
nrOpened + 1, nrOpened) == nrOpened)
+ break;
}
+
+ return await CreateNewConnectionAsync().ConfigureAwait(false);
}
private async Task<Connection> CreateNewConnectionAsync()
{
- NrConnections++;
var newConnection = _connectionFactory.CreateConnection();
await newConnection.ConnectAsync().ConfigureAwait(false);
return newConnection;
}
- private void AddConnectionIfOpen(Connection connection)
+ private Connection WaitForConnection()
{
- if (!connection.IsOpen)
+ var start = DateTimeOffset.Now;
+ var remaining = _waitForConnectionTimeout;
+ do
{
- ConsiderUnavailable();
- connection.Dispose();
- return;
- }
- AddConnection(connection);
+ if (_newConnectionAvailable.WaitOne(remaining))
--- End diff --
This loop blocks the calling thread, which is a problem as we would be
mixing async and blocking code.
We should implemented in a way that it awaits for a connection to be
available. Here are some good starting points (I'm not aware of a built-in
mechanism in .NET):
- https://github.com/StephenCleary/AsyncEx/wiki/AsyncAutoResetEvent
-
https://blogs.msdn.microsoft.com/pfxteam/2012/02/11/building-async-coordination-primitives-part-2-asyncautoresetevent/
---
