{

[FieldOffset(0)] public int Open;

[FieldOffset(4)] public int Idle;

[FieldOffset(0)] public long All;

// Busy can actually be read and written non atomically, it would introduce a benign race

// between readers of Busy and the writer(s), connector Close, when Idle is close to zero.

// The writer would first decrement Open then Idle to prevent readers racing and concluding Busy == _max.

// However with that order a race of the Idle read and decrement could happen, having readers read and

// conclude Idle > 0, causing readers to loop for a non existent connector until Idle is also decremented.

public void Deconstruct(out int open, out int idle, out int busy)

{

var copy = new PoolState { All = Volatile.Read(ref All) };

open = copy.Open;

idle = copy.Idle;

busy = copy.Open - copy.Idle;

}

public override string ToString()

{

var (open, idle, busy) = this;

return $"[{open} total, {idle} idle, {busy} busy]";

}

{

Debug.Assert(PoolSizeLimit <= short.MaxValue,

"PoolSizeLimit cannot be larger than short.MaxValue unless PoolState is refactored to hold larger values.");

if (settings.MaxPoolSize < settings.MinPoolSize)

throw new ArgumentException($"Connection can't have MaxPoolSize {settings.MaxPoolSize} under MinPoolSize {settings.MinPoolSize}");

Settings = settings;

_max = settings.MaxPoolSize;

_min = settings.MinPoolSize;

UserFacingConnectionString = settings.PersistSecurityInfo

? connString

: settings.ToStringWithoutPassword();

var connectionIdleLifetime = TimeSpan.FromSeconds(Settings.ConnectionIdleLifetime);

_pruningSamplingInterval = TimeSpan.FromSeconds(Settings.ConnectionPruningInterval);

if (connectionIdleLifetime < _pruningSamplingInterval)

throw new ArgumentException($"Connection can't have ConnectionIdleLifetime {connectionIdleLifetime} under ConnectionPruningInterval {_pruningSamplingInterval}");

_pruningMedianIndex = Divide(_pruningSampleSize, 2);

_pruningTimer = new Timer(PruningTimerCallback, this, Timeout.Infinite, Timeout.Infinite);

_pruningSampleSize = Divide(Settings.ConnectionIdleLifetime, Settings.ConnectionPruningInterval);

_pruningSamples = new int[_pruningSampleSize];

_pruningTimerEnabled = false;

_idle = new NpgsqlConnector[_max];

_open = new NpgsqlConnector[_max];

_waiting = new ConcurrentQueue<(TaskCompletionSource<NpgsqlConnector?> TaskCompletionSource, bool IsAsync)>();

{

Counters.SoftConnectsPerSecond.Increment();

// Idle may indicate that there are idle connectors, with the subsequent scan failing to find any.

// This can happen because of race conditions with Release(), which updates Idle before actually putting

// the connector in the list, or because of other allocation attempts, which remove the connector from

// the idle list before updating Idle.

// Loop until either State.Idle is 0 or you manage to remove a connector.

connector = null;

var spinner = new SpinWait();

var idle = _idle;

while (Volatile.Read(ref State.Idle) > 0)

{

for (var i = 0; connector == null && i < idle.Length; i++)

{

// First check without an Interlocked operation, it's faster

if (Volatile.Read(ref idle[i]) == null)

continue;

// If we saw a connector in this slot, atomically exchange it with a null.

// Either we get a connector out which we can use, or we get null because

// someone has taken it in the meanwhile. Either way put a null in its place.

connector = Interlocked.Exchange(ref idle[i], null);

}

if (connector == null)

{

spinner.SpinOnce();

continue;

}

Counters.NumberOfFreeConnections.Decrement();

// An connector could be broken because of a keepalive that occurred while it was

// idling in the pool

// TODO: Consider removing the pool from the keepalive code. The following branch is simply irrelevant

// if keepalive isn't turned on.

if (connector.IsBroken)

{

CloseConnector(connector, true);

continue;

}

connector.Connection = conn;

// We successfully extracted an idle connector, update state

Counters.NumberOfActiveConnections.Increment();

Interlocked.Decrement(ref State.Idle);

CheckInvariants(State);

return true;

}

connector = null;

return false;

{

// No idle connector was found in the pool.

// We now loop until one of three things happen:

// 1. The pool isn't at max capacity (Open < Max), so we can create a new physical connection.

// 2. The pool is at maximum capacity and there are no idle connectors (Open - Idle == Max),

// so we enqueue an open attempt into the waiting queue, so that the next release will unblock it.

// 3. An connector makes it into the idle list (race condition with another Release()).

while (true)

{

NpgsqlConnector? connector;

var (openCount, idleCount, busyCount) = State;

if (openCount < _max)

{

// We're under the pool's max capacity, "allocate" a slot for a new physical connection.

// Don't spin for this https://github.com/dotnet/coreclr/pull/21437

var prevOpenCount = openCount;

while (true)

{

var currentOpenCount = prevOpenCount;

prevOpenCount = Interlocked.CompareExchange(ref State.Open, currentOpenCount + 1, currentOpenCount);

// Either we succeeded or someone else did and we're at max opens, break.

if (prevOpenCount == currentOpenCount || prevOpenCount == _max) break;

}

// Restart the outer loop if we're at max opens.

if (prevOpenCount == _max) continue;

openCount = prevOpenCount + 1;

try

{

// We've managed to increase the open counter, open a physical connections.

connector = new NpgsqlConnector(conn) { ClearCounter = _clearCounter };

await connector.Open(timeout, async, cancellationToken);

}

catch

{

// Physical open failed, decrement the open and busy counter back down.

conn.Connector = null;

Interlocked.Decrement(ref State.Open);

ReleaseOneWaiter();

throw;

}

// We immediately store the connector as well, assigning it an index

// that will be used during the lifetime of the connector for both _idle and _open.

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

{

if (Interlocked.CompareExchange(ref _open[i], connector, null) == null)

{

connector.PoolIndex = i;

break;

}

}

Debug.Assert(connector.PoolIndex != int.MaxValue);

// Only when we are the ones that incremented openCount past _min Change the timer.

if (openCount == _min)

EnablePruning();

Counters.NumberOfPooledConnections.Increment();

Counters.NumberOfActiveConnections.Increment();

CheckInvariants(State);

return connector;

}

if (busyCount == _max)

{

// Pool is exhausted.

// Enqueue an allocate attempt into the waiting queue so that the next release will unblock us.

var tcs = new TaskCompletionSource<NpgsqlConnector?>(TaskCreationOptions.RunContinuationsAsynchronously);

_waiting.Enqueue((tcs, async));

// Scenario: pre-empted waiter

// Say there's a pre-emption of the thread right between our State.Busy read and our Enqueue.

// If that happens and the waiter queue is empty before we enqueue we couldn't signal to any

// releases we are a new waiter, causing any to add their connectors back into the idle pool.

// We do a correction for that right here after our own enqueue by re-checking Idle.

// We also check Open as we may have raced a connector close.

var (racedOpen, racedIdle, _) = State;

if (racedIdle > 0 || racedOpen < _max)

{

// If setting this fails we have been raced to completion by a Release().

// Otherwise we have an idle connector or open slot to try and race to.

if (tcs.TrySetCanceled())

continue;

connector = tcs.Task.Result;

// Our task completion may contain a null in order to unblock us, allowing us to try

// allocating again.

if (connector == null)

continue;

// Note that we don't update counters or any state since the connector is being

// handed off from one open connection to another.

connector.Connection = conn;

return connector;

}

try

{

if (async)

{

if (timeout.IsSet)

{

// Use Task.Delay to implement the timeout, but cancel the timer if we actually

// do complete successfully

var delayCancellationToken = new CancellationTokenSource();

using (cancellationToken.Register(s => ((CancellationTokenSource)s!).Cancel(), delayCancellationToken))

{

var timeLeft = timeout.TimeLeft;

if (timeLeft <= TimeSpan.Zero || await Task.WhenAny(tcs.Task, Task.Delay(timeLeft, delayCancellationToken.Token)) != tcs.Task)

{

// Delay task completed first, either because of a user cancellation or an actual timeout

cancellationToken.ThrowIfCancellationRequested();

throw new NpgsqlException(

$"The connection pool has been exhausted, either raise MaxPoolSize (currently {_max}) or Timeout (currently {Settings.Timeout} seconds)");

}

}

delayCancellationToken.Cancel();

}

else

{

using (cancellationToken.Register(s => ((TaskCompletionSource<NpgsqlConnector?>)s!).SetCanceled(), tcs))

await tcs.Task;

}

}

else

{

if (timeout.IsSet)

{

var timeLeft = timeout.TimeLeft;

if (timeLeft <= TimeSpan.Zero || !tcs.Task.Wait(timeLeft))

throw new NpgsqlException(

$"The connection pool has been exhausted, either raise MaxPoolSize (currently {_max}) or Timeout (currently {Settings.Timeout} seconds)");

}

else

tcs.Task.Wait();

}

}

catch

{

// We're here if the timeout expired or the cancellation token was triggered.

// Transition our Task to cancelled, so that the next time someone releases

// a connection they'll skip over it.

tcs.TrySetCanceled();

// There's still a chance of a race condition, whereby the task was transitioned to

// completed in the meantime.

if (tcs.Task.Status != TaskStatus.RanToCompletion)

throw;

}

// Note that we don't update counters since the connector is being

// handed off from one open connection to another.

Debug.Assert(tcs.Task.IsCompleted);

connector = tcs.Task.Result;

if (connector == null)

continue;

connector.Connection = conn;

return connector;

}

// We didn't create a new connector or start waiting, which means there's a new idle connector,

// or we raced a connector close, loop again as we could potentially open a new connector.

if (idleCount > 0 && TryAllocateFast(conn, out connector))

return connector;

}

// Cannot be here

}

internal void Release(NpgsqlConnector connector)

{

Counters.SoftDisconnectsPerSecond.Increment();

Counters.NumberOfActiveConnections.Decrement();

// If Clear/ClearAll has been been called since this connector was first opened,

// throw it away. The same if it's broken (in which case CloseConnector is only

// used to update state/perf counter).

if (connector.ClearCounter < _clearCounter || connector.IsBroken)

{

CloseConnector(connector, false);

return;

}

connector.Reset();

// If there are any pending waiters we hand the connector off to them directly.

while (_waiting.TryDequeue(out var waitingOpenAttempt))

{

var tcs = waitingOpenAttempt.TaskCompletionSource;

// We have a pending waiter. "Complete" it, handing off the connector.

if (tcs.TrySetResult(connector))

return;

// If the open attempt timed out, the Task's state will be set to Canceled and our

// TrySetResult fails. Try again.

Debug.Assert(tcs.Task.IsCanceled);

}

// Scenario: pre-empted release

// Right here between our check for waiters and our signalling decrement for storing

// a connector there could have been a new waiter enqueueing, we compensate at the end.

// If we're here, we put the connector back in the idle list

// We increment Idle, any allocate that is racing us will not match Busy == _max

// and will not enqueue but try to get our connector.

Interlocked.Increment(ref State.Idle);

Volatile.Write(ref _idle[connector.PoolIndex], connector);

CheckInvariants(State);

// Scenario: pre-empted release

// We checked at the start of release if there were any waiters.

// Unblock any new waiter that raced us by handing it a null result.

// We try to complete exactly one waiter as long as there are any in the queue, if any came in at all.

// The performance of trying this after each _idle release is fine as the queue is very uncontended.

// In the .Net Core BCL, 3.0 as of writing, TryDequeue for the empty path is as fast as doing IsEmpty.

ReleaseOneWaiter();

// Scenario: pre-empted waiter

// Could have a pre-empted waiter, that didn't enqueue yet it wakes up right after

// our correcting dequeue, it will do its own check after that Enqueue for Idle > 0.

}

void CloseConnector(NpgsqlConnector connector, bool wasIdle)

{

try

{

connector.Close();

}

catch (Exception e)

{

Log.Warn("Exception while closing outdated connector", e, connector.Id);

}

_open[connector.PoolIndex] = null;

int openCount;

if (wasIdle)

{

var prevAll = Volatile.Read(ref State.All);

var prevState = new PoolState { All = prevAll };

while (true)

{

var state = new PoolState { Open = prevState.Open - 1, Idle = prevState.Idle - 1 };

prevAll = Interlocked.CompareExchange(ref State.All, state.All, prevState.All);

if (prevAll == prevState.All) break;

prevState = new PoolState { All = prevAll };

}

openCount = prevState.Open - 1;

}

else

openCount = Interlocked.Decrement(ref State.Open);

// Unblock a single waiter, if any, to get the slot that just opened up.

ReleaseOneWaiter();

// Only turn off the timer one time, when it was this Close that brought Open back to _min.

if (openCount == _min)

DisablePruning();

Counters.NumberOfPooledConnections.Decrement();

CheckInvariants(State);

}

/// <summary>

/// Dequeues a single waiter and signals that it should re-attempt to allocate again. Needed in various

/// race conditions.

/// </summary>

void ReleaseOneWaiter()

{

while (_waiting.TryDequeue(out var waiter))

if (waiter.TaskCompletionSource.TrySetResult(null))

break;

}

// Manual reactivation of timer happens in callback

void EnablePruning()

{

lock (_pruningTimer)

{

_pruningTimerEnabled = true;

_pruningTimer.Change(_pruningSamplingInterval, Timeout.InfiniteTimeSpan);

}

}

void DisablePruning()

{

lock (_pruningTimer)

{

_pruningTimer.Change(Timeout.Infinite, Timeout.Infinite);

_pruningSampleIndex = 0;

_pruningTimerEnabled = false;

}

}

static void PruneIdleConnectors(object? state)

{

var pool = (ConnectorPool)state!;

var samples = pool._pruningSamples;

int toPrune;

lock (pool._pruningTimer)

{

// Check if we might have been contending with DisablePruning.

if (!pool._pruningTimerEnabled)

return;

var sampleIndex = pool._pruningSampleIndex;

if (sampleIndex < pool._pruningSampleSize)

{

samples[sampleIndex] = pool.State.Idle;

pool._pruningSampleIndex = sampleIndex + 1;

pool._pruningTimer.Change(pool._pruningSamplingInterval, Timeout.InfiniteTimeSpan);

return;

}

// Calculate median value for pruning, reset index and timer, and release the lock.

Array.Sort(samples);

toPrune = samples[pool._pruningMedianIndex];

pool._pruningSampleIndex = 0;

pool._pruningTimer.Change(pool._pruningSamplingInterval, Timeout.InfiniteTimeSpan);

}

var idle = pool._idle;

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

{

if (Volatile.Read(ref pool.State.Open) <= pool._min || toPrune == 0)

return;

var connector = Interlocked.Exchange(ref idle[i], null);

if (connector == null) continue;

toPrune -= 1;

pool.CloseConnector(connector, true);

}

}

internal void Clear()

{

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

{

var connector = Interlocked.Exchange(ref _idle[i], null);

if (connector != null)

CloseConnector(connector, true);

}

_clearCounter++;

}

#region Pending Enlisted Connections

internal void AddPendingEnlistedConnector(NpgsqlConnector connector, Transaction transaction)

{

lock (_pendingEnlistedConnectors)

{

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

list = _pendingEnlistedConnectors[transaction] = new List<NpgsqlConnector>();

list.Add(connector);

}

}

internal void TryRemovePendingEnlistedConnector(NpgsqlConnector connector, Transaction transaction)

{

lock (_pendingEnlistedConnectors)

{

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

return;

list.Remove(connector);

if (list.Count == 0)

_pendingEnlistedConnectors.Remove(transaction);

}

}

internal NpgsqlConnector? TryAllocateEnlistedPending(Transaction transaction)

{

lock (_pendingEnlistedConnectors)

{

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

return null;

var connector = list[list.Count - 1];

list.RemoveAt(list.Count - 1);

if (list.Count == 0)

_pendingEnlistedConnectors.Remove(transaction);

return connector;

}

}

// Note that while the dictionary is thread-safe, we assume that the lists it contains don't need to be

// (i.e. access to connectors of a specific transaction won't be concurrent)

readonly Dictionary<Transaction, List<NpgsqlConnector>> _pendingEnlistedConnectors

= new Dictionary<Transaction, List<NpgsqlConnector>>();

#endregion

#region Misc

static int Divide(int value, int divisor) => 1 + (value - 1) / divisor;

[Conditional("DEBUG")]

void CheckInvariants(PoolState state)

{

if (state.Open > _max)

throw new NpgsqlException($"Pool is over capacity (Total={state.Open}, Max={_max})");

if (state.Open < 0)

throw new NpgsqlException("Open is negative");

if (state.Idle < 0)

throw new NpgsqlException("Idle is negative");

if (state.Open - state.Idle < 0)

throw new NpgsqlException("Busy is negative");

}

public void Dispose() => _pruningTimer?.Dispose();

public override string ToString() => State.ToString();

#endregion Misc

}