SNOW-984600 Avoid closing expired sessions synchronously with obtaine… (

#841)

…d lock (#830)

### Description
Avoid closing expired sessions synchronously with obtained lock

### Checklist
- [x] Code compiles correctly
- [x] Code is formatted according to [Coding
Conventions](../CodingConventions.md)
- [x] Created tests which fail without the change (if possible)
- [x] All tests passing (`dotnet test`)
- [x] Extended the README / documentation, if necessary
- [x] Provide JIRA issue id (if possible) or GitHub issue id in PR name

Snowflake.Data.Tests/IntegrationTests/SFConnectionIT.cs

@@ -1780,8 +1780,8 @@ public void TestAsyncLoginTimeout()
 
                 // Should timeout after the defined timeout since retry count is infinite
                 Assert.GreaterOrEqual(stopwatch.ElapsedMilliseconds, timeoutSec * 1000 - delta);
-                // But never more than 1 sec (buffer time) after the defined timeout
-                Assert.LessOrEqual(stopwatch.ElapsedMilliseconds, (timeoutSec + 1) * 1000);
+                // But never more than 3 sec (buffer time) after the defined timeout
+                Assert.LessOrEqual(stopwatch.ElapsedMilliseconds, (timeoutSec + 3) * 1000);
 
                 Assert.AreEqual(ConnectionState.Closed, conn.State);
                 Assert.AreEqual(timeoutSec, conn.ConnectionTimeout);
@@ -1818,8 +1818,8 @@ public void TestAsyncLoginTimeoutWithRetryTimeoutLesserThanConnectionTimeout()
 
                 // Should timeout after the defined timeout since retry count is infinite
                 Assert.GreaterOrEqual(stopwatch.ElapsedMilliseconds, retryTimeout * 1000 - delta);
-                // But never more than 1 sec (buffer time) after the defined timeout
-                Assert.LessOrEqual(stopwatch.ElapsedMilliseconds, (retryTimeout + 1) * 1000);
+                // But never more than 2 sec (buffer time) after the defined timeout
+                Assert.LessOrEqual(stopwatch.ElapsedMilliseconds, (retryTimeout + 2) * 1000);
 
                 Assert.AreEqual(ConnectionState.Closed, conn.State);
                 Assert.AreEqual(retryTimeout, conn.ConnectionTimeout);

Snowflake.Data.Tests/IntegrationTests/SFConnectionPoolIT.cs

@@ -12,6 +12,7 @@
 using Snowflake.Data.Client;
 using Snowflake.Data.Log;
 using NUnit.Framework;
+using Snowflake.Data.Core.Session;
 
 namespace Snowflake.Data.Tests.IntegrationTests
 {
@@ -395,5 +396,31 @@ public void TestConnectionPoolTurnOff()
             SnowflakeDbConnectionPool.SetPooling(false);
             //Put a breakpoint at SFSession close function, after connection pool is off, it will send close session request.
         }
+
+        [Test]
+        public void TestCloseSessionAfterTimeout()
+        {
+            // arrange
+            const int SessionTimeoutSeconds = 2;
+            const int TimeForBackgroundSessionCloseMillis = 2000;
+            SnowflakeDbConnectionPool.SetTimeout(SessionTimeoutSeconds);
+            var conn1 = new SnowflakeDbConnection(ConnectionString);
+            conn1.Open();
+            var session = conn1.SfSession;
+            conn1.Close();
+            Assert.IsTrue(session.IsEstablished());
+            Thread.Sleep(SessionTimeoutSeconds * 1000); // wait until the session is expired
+            var conn2 = new SnowflakeDbConnection(ConnectionString);
+
+            // act
+            conn2.Open(); // it gets a session from the caching pool firstly closing session of conn1 in background
+            Thread.Sleep(TimeForBackgroundSessionCloseMillis); // wait for closing expired session
+
+            // assert
+            Assert.IsFalse(session.IsEstablished());
+
+            // cleanup
+            conn2.Close();
+        }
     }
 }

Snowflake.Data/Core/Session/SFSession.cs

@@ -242,7 +242,7 @@ internal async Task OpenAsync(CancellationToken cancellationToken)
         internal void close()
         {
             // Nothing to do if the session is not open
-            if (null == sessionToken) return;
+            if (!IsEstablished()) return;
 
             stopHeartBeatForThisSession();
 
@@ -274,7 +274,7 @@ internal void close()
         internal async Task CloseAsync(CancellationToken cancellationToken)
         {
             // Nothing to do if the session is not open
-            if (null == sessionToken) return;
+            if (!IsEstablished()) return;
 
             stopHeartBeatForThisSession();
 
@@ -303,6 +303,8 @@ internal async Task CloseAsync(CancellationToken cancellationToken)
             sessionToken = null;
         }
 
+        internal bool IsEstablished() => sessionToken != null;
+
         internal void renewSession()
         {
             logger.Info("Renew the session.");
@@ -504,7 +506,7 @@ internal void heartbeat()
             logger.Debug("heartbeat");
 
             bool retry = false;
-            if (sessionToken != null)
+            if (IsEstablished())
             {
                 do
                 {

Snowflake.Data/Core/Session/SessionPool.cs

@@ -57,8 +57,8 @@ private void CleanExpiredSessions()
                 {
                     if (item.IsExpired(_timeout, timeNow))
                     {
+                        Task.Run(() => item.close());
                         _sessions.Remove(item);
-                        item.close();
                     }
                 }
             }
@@ -96,7 +96,7 @@ private SFSession GetIdleSession(string connStr)
                         long timeNow = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
                         if (session.IsExpired(_timeout, timeNow))
                         {
-                            session.close();
+                            Task.Run(() => session.close());
                             i--;
                         }
                         else
@@ -187,7 +187,7 @@ internal void ClearAllPools()
             {
                 foreach (SFSession session in _sessions)
                 {
-                    session.close();
+                    session.close(); // it is left synchronously here because too much async tasks slows down testing
                 }
                 _sessions.Clear();
             }