{

var hosts = settings.Host!.Split(',');

_pools = new ConnectorSource[hosts.Length];

for (var i = 0; i < hosts.Length; i++)

{

var poolSettings = settings.Clone();

Debug.Assert(!poolSettings.Multiplexing);

var host = hosts[i].AsSpan().Trim();

if (NpgsqlConnectionStringBuilder.TrySplitHostPort(host, out var newHost, out var newPort))

{

poolSettings.Host = newHost;

poolSettings.Port = newPort;

}

else

poolSettings.Host = host.ToString();

_pools[i] = settings.Pooling

? new ConnectorPool(poolSettings, poolSettings.ConnectionString, this)

: new UnpooledConnectorSource(poolSettings, poolSettings.ConnectionString);

}

=> state switch

{

ClusterState.Offline => false,

ClusterState.Unknown => true, // We will check compatibility again after refreshing the cluster state

ClusterState.PrimaryReadWrite when preferredType == TargetSessionAttributes.Primary || preferredType == TargetSessionAttributes.PreferPrimary

|| preferredType == TargetSessionAttributes.ReadWrite => true,

ClusterState.PrimaryReadOnly when preferredType == TargetSessionAttributes.Primary || preferredType == TargetSessionAttributes.PreferPrimary

|| preferredType == TargetSessionAttributes.ReadOnly => true,

ClusterState.Standby when preferredType == TargetSessionAttributes.Standby || preferredType == TargetSessionAttributes.PreferStandby

|| preferredType == TargetSessionAttributes.ReadOnly => true,

_ => preferredType == TargetSessionAttributes.Any

=> state switch

{

ClusterState.Unknown => true, // We will check compatibility again after refreshing the cluster state

ClusterState.PrimaryReadWrite when preferredType == TargetSessionAttributes.PreferPrimary || preferredType == TargetSessionAttributes.PreferStandby => true,

ClusterState.PrimaryReadOnly when preferredType == TargetSessionAttributes.PreferPrimary || preferredType == TargetSessionAttributes.PreferStandby => true,

ClusterState.Standby when preferredType == TargetSessionAttributes.PreferPrimary || preferredType == TargetSessionAttributes.PreferStandby => true,

_ => false

TargetSessionAttributes preferredType, Func<ClusterState, TargetSessionAttributes, bool> clusterValidator, int poolIndex,

IList<Exception> exceptions, CancellationToken cancellationToken)

{

var pools = _pools;

for (var i = 0; i < pools.Length; i++)

{

var pool = pools[poolIndex];

poolIndex++;

if (poolIndex == pools.Length)

poolIndex = 0;

var clusterState = GetClusterState(pool);

if (!clusterValidator(clusterState, preferredType))

continue;

NpgsqlConnector? connector = null;

try

{

if (pool.TryGetIdleConnector(out connector))

{

if (clusterState == ClusterState.Unknown)

{

clusterState = await connector.QueryClusterState(new NpgsqlTimeout(timeoutPerHost), async, cancellationToken);

Debug.Assert(clusterState != ClusterState.Unknown);

if (!clusterValidator(clusterState, preferredType))

{

pool.Return(connector);

continue;

}

}

return connector;

}

else

{

connector = await pool.OpenNewConnector(conn, new NpgsqlTimeout(timeoutPerHost), async, cancellationToken);

if (connector is not null)

{

if (clusterState == ClusterState.Unknown)

{

clusterState = await connector.QueryClusterState(new NpgsqlTimeout(timeoutPerHost), async, cancellationToken);

Debug.Assert(clusterState != ClusterState.Unknown);

if (!clusterValidator(clusterState, preferredType))

{

pool.Return(connector);

continue;

}

}

return connector;

}

}

}

catch (Exception ex)

{

exceptions.Add(ex);

if (connector is not null)

pool.Return(connector);

}

}

return null;

Func<ClusterState, TargetSessionAttributes, bool> clusterValidator, int poolIndex,

IList<Exception> exceptions, CancellationToken cancellationToken)

{

var pools = _pools;

for (var i = 0; i < pools.Length; i++)

{

var pool = pools[poolIndex];

poolIndex++;

if (poolIndex == pools.Length)

poolIndex = 0;

var clusterState = GetClusterState(pool);

if (!clusterValidator(clusterState, preferredType))

continue;

NpgsqlConnector? connector = null;

try

{

connector = await pool.Get(conn, new NpgsqlTimeout(timeoutPerHost), async, cancellationToken);

if (clusterState == ClusterState.Unknown)

{

// Get might have opened a new physical connection and refreshed the cluster state, check again

clusterState = GetClusterState(pool);

if (clusterState == ClusterState.Unknown)

clusterState = await connector.QueryClusterState(new NpgsqlTimeout(timeoutPerHost), async, cancellationToken);

Debug.Assert(clusterState != ClusterState.Unknown);

if (!clusterValidator(clusterState, preferredType))

{

pool.Return(connector);

continue;

}

}

return connector;

}

catch (Exception ex)

{

exceptions.Add(ex);

if (connector is not null)

pool.Return(connector);

}

}

return null;

{

var exceptions = new List<Exception>();

var poolIndex = conn.Settings.LoadBalanceHosts ? GetRoundRobinIndex() : 0;

var timeoutPerHost = timeout.IsSet ? timeout.CheckAndGetTimeLeft() : TimeSpan.Zero;

var preferredType = GetTargetSessionAttributes(conn);

var checkUnpreferred =

preferredType == TargetSessionAttributes.PreferPrimary ||

preferredType == TargetSessionAttributes.PreferStandby;

var connector = await TryGetIdleOrNew(conn, timeoutPerHost, async, preferredType, IsPreferred, poolIndex, exceptions, cancellationToken) ??

(checkUnpreferred ?

await TryGetIdleOrNew(conn, timeoutPerHost, async, preferredType, IsFallbackOrPreferred, poolIndex, exceptions, cancellationToken)

: null) ??

await TryGet(conn, timeoutPerHost, async, preferredType, IsPreferred, poolIndex, exceptions, cancellationToken) ??

(checkUnpreferred ?

await TryGet(conn, timeoutPerHost, async, preferredType, IsFallbackOrPreferred, poolIndex, exceptions, cancellationToken)

: null);

if (connector is not null)

return connector;

throw NoSuitableHostsException(exceptions);

}

static NpgsqlException NoSuitableHostsException(IList<Exception> exceptions)

=> exceptions.Count == 0

? new NpgsqlException("No suitable host was found.")

: exceptions[0] is PostgresException firstException &&

exceptions.All(x => x is PostgresException ex && ex.SqlState == firstException.SqlState)

? firstException

: new NpgsqlException("Unable to connect to a suitable host. Check inner exception for more details.",

new AggregateException(exceptions));

int GetRoundRobinIndex()

{

while (true)

{

var index = Interlocked.Increment(ref _roundRobinIndex);

if (index >= 0)

return index % _pools.Length;

// Worst case scenario - we've wrapped around integer counter

if (index == int.MinValue)

{

// This is the thread which wrapped around the counter - reset it to 0

_roundRobinIndex = 0;

return 0;

}

// This is not the thread which wrapped around the counter - just wait until it's 0 or more

var sw = new SpinWait();

while (_roundRobinIndex < 0)

sw.SpinOnce();

}

}

internal override void Return(NpgsqlConnector connector)

=> throw new NpgsqlException("Npgsql bug: a connector was returned to " + nameof(MultiHostConnectorPool));

internal override bool TryGetIdleConnector([NotNullWhen(true)] out NpgsqlConnector? connector)

=> throw new NpgsqlException("Npgsql bug: trying to get an idle connector from " + nameof(MultiHostConnectorPool));

internal override ValueTask<NpgsqlConnector?> OpenNewConnector(NpgsqlConnection conn, NpgsqlTimeout timeout, bool async, CancellationToken cancellationToken)

=> throw new NpgsqlException("Npgsql bug: trying to open a new connector from " + nameof(MultiHostConnectorPool));

internal override void Clear()

{

foreach (var pool in _pools)

pool.Clear();

}

internal override (int Total, int Idle, int Busy) Statistics

{

get

{

var numConnectors = 0;

var idleCount = 0;

foreach (var pool in _pools)

{

var stat = pool.Statistics;

numConnectors += stat.Total;

idleCount += stat.Idle;

}

return (numConnectors, idleCount, numConnectors - idleCount);

}

}

internal override bool TryRentEnlistedPending(Transaction transaction, NpgsqlConnection connection,

[NotNullWhen(true)] out NpgsqlConnector? connector)

{

lock (_pendingEnlistedConnectors)

{

if (!_pendingEnlistedConnectors.TryGetValue(transaction, out var list))

{

connector = null;

return false;

}

for (var i = list.Count - 1; i >= 0; i--)

{

connector = list[i];

var lastKnownState = GetClusterState(connector.Host, connector.Port, ignoreExpiration: true);

Debug.Assert(lastKnownState != ClusterState.Unknown);

var preferredType = GetTargetSessionAttributes(connection);

if (IsFallbackOrPreferred(lastKnownState, preferredType))

{

list.RemoveAt(i);

if (list.Count == 0)

_pendingEnlistedConnectors.Remove(transaction);

return true;

}

}

connector = null;

return false;

}

}

static TargetSessionAttributes GetTargetSessionAttributes(NpgsqlConnection connection)

=> connection.Settings.TargetSessionAttributesParsed ??

(PostgresEnvironment.TargetSessionAttributes is string s

? NpgsqlConnectionStringBuilder.ParseTargetSessionAttributes(s)

: default);