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PoolManager.cs
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123 lines (109 loc) · 4.16 KB
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using System;
using System.Diagnostics;
using System.Threading;
namespace Npgsql
{
/// <summary>
/// Provides lookup for a pool based on a connection string.
/// </summary>
/// <remarks>
/// <see cref="TryGetValue"/> is lock-free, to avoid contention, but the same isn't
/// true of <see cref="GetOrAdd"/>, which acquires a lock. The calling code always tries
/// <see cref="TryGetValue"/> before trying to <see cref="GetOrAdd"/>.
/// </remarks>
static class PoolManager
{
internal const int InitialPoolsSize = 10;
static readonly object _lock = new object();
static (string Key, ConnectorPool Pool)[] _pools = new (string, ConnectorPool)[InitialPoolsSize];
static int _nextSlot;
internal static bool TryGetValue(string key, out ConnectorPool pool)
{
// Note that pools never get removed. _pools is strictly append-only.
var pools = _pools;
var sw = new SpinWait();
// First scan the pools and do reference equality on the connection strings
for (var i = 0; i < _nextSlot; i++)
{
if (ReferenceEquals(pools[i].Key, key))
{
// It's possible that this pool entry is currently being written: the connection string
// component has already been writte, but the pool component is just about to be. So we
// loop on the pool until it's non-null
while (Volatile.Read(ref pools[i].Pool) == null)
sw.SpinOnce();
pool = pools[i].Pool;
return true;
}
}
// Next try value comparison on the strings
for (var i = 0; i < _nextSlot; i++)
{
if (pools[i].Key == key)
{
// See comment above
while (Volatile.Read(ref pools[i].Pool) == null)
sw.SpinOnce();
pool = pools[i].Pool;
return true;
}
}
pool = null;
return false;
}
internal static ConnectorPool GetOrAdd(string key, ConnectorPool pool)
{
lock (_lock)
{
if (TryGetValue(key, out var result))
return result;
// May need to grow the array.
if (_nextSlot == _pools.Length)
{
var newPools = new (string, ConnectorPool)[_pools.Length * 2];
Array.Copy(_pools, newPools, _pools.Length);
Interlocked.Exchange(ref _pools, newPools);
}
_pools[_nextSlot].Key = key;
_pools[_nextSlot].Pool = pool;
Interlocked.Increment(ref _nextSlot);
return pool;
}
}
internal static void Clear(string connString)
{
Debug.Assert(connString != null);
if (TryGetValue(connString, out var pool))
pool.Clear();
}
internal static void ClearAll()
{
for (var i = 0; i < _nextSlot; i++)
{
if (_pools[i].Key == null)
return;
_pools[i].Pool?.Clear();
}
}
static PoolManager()
{
// When the appdomain gets unloaded (e.g. web app redeployment) attempt to nicely
// close idle connectors to prevent errors in PostgreSQL logs (#491).
AppDomain.CurrentDomain.DomainUnload += (sender, args) => ClearAll();
AppDomain.CurrentDomain.ProcessExit += (sender, args) => ClearAll();
}
/// <summary>
/// Resets the pool manager to its initial state, for test purposes only.
/// Assumes that no other threads are accessing the pool.
/// </summary>
internal static void Reset()
{
lock (_lock)
{
ClearAll();
_pools = new (string, ConnectorPool)[InitialPoolsSize];
_nextSlot = 0;
}
}
}
}