Move procedure cache to connection pool. Fixes #415

Author: bgrainger

src/MySqlConnector/Core/ConnectionPool.cs

@@ -166,6 +166,7 @@ public async Task ClearAsync(IOBehavior ioBehavior, CancellationToken cancellati
 			// increment the generation of the connection pool
 			Log.Info("{0} clearing connection pool", m_logArguments);
 			Interlocked.Increment(ref m_generation);
+			m_procedureCache = null;
 			RecoverLeakedSessions();
 			await CleanPoolAsync(ioBehavior, session => session.PoolGeneration != m_generation, false, cancellationToken).ConfigureAwait(false);
 		}
@@ -179,6 +180,23 @@ public async Task ReapAsync(IOBehavior ioBehavior, CancellationToken cancellatio
 			await CleanPoolAsync(ioBehavior, session => (DateTime.UtcNow - session.LastReturnedUtc).TotalSeconds >= m_connectionSettings.ConnectionIdleTimeout, true, cancellationToken).ConfigureAwait(false);
 		}
 
+		/// <summary>
+		/// Returns the stored procedure cache for this <see cref="ConnectionPool"/>, lazily creating it on demand.
+		/// This method may return a different object after <see cref="ClearAsync"/> has been called. The returned
+		/// object is shared between multiple threads and is only safe to use after taking a <c>lock</c> on the
+		/// object itself.
+		/// </summary>
+		public Dictionary<string, CachedProcedure> GetProcedureCache()
+		{
+			var procedureCache = m_procedureCache;
+			if (procedureCache == null)
+			{
+				var newProcedureCache = new Dictionary<string, CachedProcedure>();
+				procedureCache = Interlocked.CompareExchange(ref m_procedureCache, newProcedureCache, null) ?? newProcedureCache;
+			}
+			return procedureCache;
+		}
+		
 		/// <summary>
 		/// Examines all the <see cref="ServerSession"/> objects in <see cref="m_leasedSessions"/> to determine if any
 		/// have an owning <see cref="MySqlConnection"/> that has been garbage-collected. If so, assumes that the connection
@@ -461,5 +479,6 @@ public IEnumerable<string> LoadBalance(IReadOnlyList<string> hosts)
 		readonly object[] m_logArguments;
 		uint m_lastRecoveryTime;
 		int m_lastSessionId;
+		Dictionary<string, CachedProcedure> m_procedureCache;
 	}
 }

src/MySqlConnector/MySql.Data.MySqlClient/MySqlConnection.cs

@@ -302,14 +302,19 @@ internal async Task<CachedProcedure> GetCachedProcedure(IOBehavior ioBehavior, s
 			if (m_session.ServerVersion.Version < ServerVersions.SupportsProcedureCache)
 				return null;
 
-			if (m_cachedProcedures == null)
-				m_cachedProcedures = new Dictionary<string, CachedProcedure>();
+			var cachedProcedures = m_session.Pool?.GetProcedureCache() ?? m_cachedProcedures;
+			if (cachedProcedures == null)
+				cachedProcedures = m_cachedProcedures = new Dictionary<string, CachedProcedure>();
 
 			var normalized = NormalizedSchema.MustNormalize(name, Database);
-			if (!m_cachedProcedures.TryGetValue(normalized.FullyQualified, out var cachedProcedure))
+			CachedProcedure cachedProcedure;
+			lock (cachedProcedures)
+				cachedProcedures.TryGetValue(normalized.FullyQualified, out cachedProcedure);
+			if (cachedProcedure == null)
 			{
 				cachedProcedure = await CachedProcedure.FillAsync(ioBehavior, this, normalized.Schema, normalized.Component, cancellationToken).ConfigureAwait(false);
-				m_cachedProcedures[normalized.FullyQualified] = cachedProcedure;
+				lock (cachedProcedures)
+					cachedProcedures[normalized.FullyQualified] = cachedProcedure;
 			}
 			return cachedProcedure;
 		}