From 52eb23c43b1c9cf1e11e0a438f8cce17dafdbeec Mon Sep 17 00:00:00 2001
From: Elte Hupkes <eltehupkes@srxp.com>
Date: Thu, 29 Aug 2019 14:04:39 +0200
Subject: [PATCH 1/2] Fix to #761, preventing incorrect disposed command object

This addresses a race condition where a new PreparedSqliteInsertCommand object was returned in a disposed state if a second object was created and inserted into the command map during its creation. The fix always returns the item inserted into the command map.
---
 src/SQLite.cs | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/src/SQLite.cs b/src/SQLite.cs
index 0ce075e0..c1eac952 100644
--- a/src/SQLite.cs
+++ b/src/SQLite.cs
@@ -1710,21 +1710,20 @@ PreparedSqlLiteInsertCommand GetInsertCommand (TableMapping map, string extra)
 			var key = Tuple.Create (map.MappedType.FullName, extra);
 
 			lock (_insertCommandMap) {
-				_insertCommandMap.TryGetValue (key, out prepCmd);
+				if (_insertCommandMap.TryGetValue (key, out prepCmd)) {
+					return prepCmd;
+				}
 			}
 
-			if (prepCmd == null) {
-				prepCmd = CreateInsertCommand (map, extra);
-				var added = false;
-				lock (_insertCommandMap) {
-					if (!_insertCommandMap.ContainsKey (key)) {
-						_insertCommandMap.Add (key, prepCmd);
-						added = true;
-					}
-				}
-				if (!added) {
+			prepCmd = CreateInsertCommand (map, extra);
+			
+			lock (_insertCommandMap) {
+				if (_insertCommandMap.TryGetValue (key, out var existing)) {
 					prepCmd.Dispose ();
+					return existing;
 				}
+
+				_insertCommandMap.Add (key, prepCmd);
 			}
 
 			return prepCmd;

From 3826756ffbb0185df8c38a45544b7a7066e6236f Mon Sep 17 00:00:00 2001
From: Elte Hupkes <eltehupkes@srxp.com>
Date: Thu, 29 Aug 2019 14:40:57 +0200
Subject: [PATCH 2/2] Adding a regression test for #761

---
 tests/ConcurrencyTest.cs | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/tests/ConcurrencyTest.cs b/tests/ConcurrencyTest.cs
index 358a1133..ebf865bd 100644
--- a/tests/ConcurrencyTest.cs
+++ b/tests/ConcurrencyTest.cs
@@ -187,7 +187,28 @@ public void TestLoad()
             }
         }
 
-
+        /// <summary>
+        /// Test for issue #761. Because the nature of this test is a race condition,
+        /// it is not guaranteed to fail if the issue is present. It does appear to
+        /// fail most of the time, though.
+        /// </summary>
+        [Test]
+        public void TestInsertCommandCreation ()
+        {
+	        using (var dbConnection =
+		        new DbConnection (SQLiteOpenFlags.FullMutex | SQLiteOpenFlags.ReadWrite | SQLiteOpenFlags.Create)) {
+		        var obj1 = new TestObj ();
+		        var obj2 = new TestObj ();
+		        var taskA = Task.Run (() => {
+			        dbConnection.Insert (obj1);
+		        });
+		        var taskB = Task.Run (() => {
+			        dbConnection.Insert (obj2);
+		        });
+
+		        Task.WhenAll (taskA, taskB).Wait ();
+	        }
+        }
     }
 }