Only close cursor when it wasn't closed for us.

Author: CoreyKaylor

src/LightningDB.Tests/CursorTests.cs

@@ -60,8 +60,6 @@ public void CursorShouldPutValues()
         _env.RunCursorScenario((tx, _, c) =>
         {
             PopulateCursorValues(c);
-            c.Dispose();
-            //TODO evaluate how not to require this Dispose likely due to #155
             var result = tx.Commit();
             Assert.Equal(MDBResultCode.Success, result);
         });
@@ -362,4 +360,41 @@ public void ShouldDeleteDuplicates()
             Assert.Equal(MDBResultCode.NotFound, result);
         }, DatabaseOpenFlags.DuplicatesFixed | DatabaseOpenFlags.Create);  
     }
+
+    [Fact]
+    public void CanPutBatchesViaCursorIssue155()
+    {
+        static LightningDatabase OpenDatabase(LightningEnvironment environment)
+        {
+            using var tx = environment.BeginTransaction();
+            var db = tx.OpenDatabase(configuration: new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create });
+            tx.Commit();
+            return db;
+        }
+
+        void ReproduceCoreIteration(LightningEnvironment environment, LightningDatabase db)
+        {
+            using var tx = environment.BeginTransaction(); //auto-disposed at end of scope
+            using var cursor = tx.CreateCursor(db); //auto-disposed at end of scope
+
+            var guid = Guid.NewGuid().ToString();
+            var guidBytes = UTF8.GetBytes(guid);
+
+            _ = cursor.Put(
+                guidBytes,
+                guidBytes,
+                CursorPutOptions.None
+            );
+
+            tx.Commit().ThrowOnError();
+        }
+
+        using var db = OpenDatabase(_env);
+
+        for (var i = 0; i < 5000; i++)
+        {
+            ReproduceCoreIteration(_env, db);
+        }
+        Assert.True(true, "Code would be unreachable otherwise.");
+    }
 }

src/LightningDB/LightningCursor.cs

@@ -29,6 +29,7 @@ internal LightningCursor(LightningDatabase db, LightningTransaction txn)
         mdb_cursor_open(txn.Handle(), db.Handle(), out _handle).ThrowOnError();
 
         Transaction = txn;
+        Transaction.ShouldCloseCursor = true;
         Transaction.Disposing += Dispose;
     }
 
@@ -503,14 +504,17 @@ public MDBResultCode Renew(LightningTransaction txn)
     /// <param name="disposing">True if called from Dispose.</param>
     private void Dispose(bool disposing)
     {
-        if (_handle == 0)
+        if (_handle == default)
             return;
 
         if (!disposing)
             throw new InvalidOperationException("The LightningCursor was not disposed and cannot be reliably dealt with from the finalizer");
 
-        mdb_cursor_close(_handle);
-        _handle = 0;
+        if (Transaction.ShouldCloseCursor)
+        {
+            mdb_cursor_close(_handle);
+        }
+        _handle = default;
 
         Transaction.Disposing -= Dispose;
 

src/LightningDB/LightningDatabase.cs

@@ -86,6 +86,7 @@ public Stats DatabaseStats
     public MDBResultCode Drop(LightningTransaction transaction)
     {
         var result = mdb_drop(transaction.Handle(), _handle, true);
+        _transaction.ShouldCloseCursor = false;
         IsOpened = false;
         _handle = default;
         return result;

src/LightningDB/LightningTransaction.cs

@@ -59,6 +59,8 @@ private void OnParentStateChanging(LightningTransactionState state)
 
     public event Action Disposing;
     private event Action<LightningTransactionState> StateChanging;
+    
+    internal bool ShouldCloseCursor { get; set; }
 
     /// <summary>
     /// Current transaction state.
@@ -295,6 +297,7 @@ public MDBResultCode Renew()
     public MDBResultCode Commit()
     {
         State = LightningTransactionState.Committed;
+        ShouldCloseCursor = false;
         StateChanging?.Invoke(State);
         return mdb_txn_commit(_handle);
     }