SNOW-937190 max pool size reached with wait support and timeout excep…

…tion

Snowflake.Data/Core/Session/SessionPool.cs

@@ -26,7 +26,9 @@ sealed class SessionPool : IDisposable
         private SecureString _password;
         private bool _pooling = true;
         private int _busySessions;
-        private bool _allowExceedMaxPoolSize = true;
+        private bool _allowExceedMaxPoolSize = true; // differentiates behavior when max size reached
+        private int _waitForIdleSessionSleepTimeout = 5;
+        private int _waitForIdleSessionTimeout = 120;
 
         internal SessionPool()
         {
@@ -43,7 +45,7 @@ internal SessionPool(string connectionString, SecureString password) : this()
         {
             _connectionString = connectionString;
             _password = password;
-            _allowExceedMaxPoolSize = false; // TODO: SNOW-937190
+            _allowExceedMaxPoolSize = false;
         }
 
         internal static SessionPool CreateSessionPoolV1() => new SessionPool();
@@ -133,6 +135,11 @@ private SFSession GetIdleSession(string connStr)
         private SFSession NewSession(String connectionString, SecureString password)
         {
             s_logger.Debug("SessionPool::NewSession");
+            if (!_allowExceedMaxPoolSize && GetCurrentPoolSize() >= MaxPoolSize)
+            {
+                s_logger.Warn("Max pool size reached");
+                return WaitForPooledSession(CancellationToken.None);
+            }
             try
             {
                 var session = new SFSession(connectionString, password);
@@ -156,6 +163,11 @@ private SFSession NewSession(String connectionString, SecureString password)
         private Task<SFSession> NewSessionAsync(String connectionString, SecureString password, CancellationToken cancellationToken)
         {
             s_logger.Debug("SessionPool::NewSessionAsync");
+            if (!_allowExceedMaxPoolSize && GetCurrentPoolSize() >= MaxPoolSize)
+            {
+                s_logger.Warn("Max pool size reached");
+                return Task.Run(() => WaitForPooledSession(cancellationToken), cancellationToken);
+            }
             var session = new SFSession(connectionString, password);
             _busySessions++;
             return session
@@ -174,12 +186,46 @@ private Task<SFSession> NewSessionAsync(String connectionString, SecureString pa
                     return session;
                 }, TaskContinuationOptions.NotOnCanceled);
         }
+
+        private SFSession WaitForPooledSession(CancellationToken cancellationToken)
+        {
+            if (!_pooling)
+                return null;
+
+            long start = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
+            while (true)
+            {
+                if (cancellationToken.IsCancellationRequested)
+                    cancellationToken.ThrowIfCancellationRequested();
+
+                lock (s_sessionPoolLock)
+                {
+                    var session = GetIdleSession(_connectionString);
+                    if (session != null)
+                    {
+                        _idleSessions.Remove(session);
+                        _busySessions++;
+                        return session;
+                    }
+                }
+
+                Thread.Sleep(_waitForIdleSessionSleepTimeout);
+                long now = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
+                if (start + _waitForIdleSessionTimeout < now)
+                    throw new SnowflakeDbException(
+                        new TimeoutException("No free connections in the pool."), // TODO:
+                        SnowflakeDbException.CONNECTION_FAILURE_SSTATE,
+                        SFError.REQUEST_TIMEOUT, 
+                        "Unable to connect.");
+            }
+        }
 
         internal bool AddSession(SFSession session)
         {
             s_logger.Debug("SessionPool::AddSession");
             if (!_pooling)
                 return false;
+
             long timeNow = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
             if (session.IsNotOpen() || session.IsExpired(_timeout, timeNow))
             {