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misha256
misha256

Reputation: 347

What happens to DataRow objects when Dispose is called on a DataTable?

Here's where .NET starts to do my head in. Consider the following scenario:

  1. I have a DataTable object, containing a number of DataRow objects
  2. I add some of the DataRow objects to an Array
  3. I call Dispose on the DataTable.

What guarantee do I have that calling Dispose on the DataTable won't compromise the DataRow objects (which, by reference, would affect those added to the Array)?

MS documentation is zero help in this case.

EDIT: So far folks have missed the point entirely. IDisposable objects are meant to be disposed of as soon as possible. My code is going to be creating thousands of DataTable objects during a typical day. No way am I leaving those un-disposed if they implement IDispoable.

BUT, I need the handful of DataRow objects to stay alive because that's what my 3rd-party binary (which I have no control over) expects. And I need them to stay alive for significantly longer than the DataTable objects.

All I need is authoritative information that describes what Dispose on a DataTable actually does. Looks like said information does not exist, which is why I'm asking here for help. Someone may have a reference, or documentation I have overlooked, that answers my need.

EDIT 2: I have tested as Blam suggested, including adding GC.Collect + a bonus GC.WaitForPendingFinalizers + one more GC.Collect after disposing the DataTable. The DataRows appear to be fine, still alive and accessible. That's positive, but alas not authoritative enough to include in production code :-(

Upvotes: 1

Views: 2046

Answers (2)

moribvndvs
moribvndvs

Reputation: 42497

DataTable doesn't re-implement MarshalByValueComponent.Dispose, and that method doesn't really do much on its own. So in effect, calling DataTable.Dispose doesn't do anything to the table or the data it contains. Interestingly enough, DataTable even goes so far to suppress finalization in the constructor, because it doesn't hold unmanaged resources.

Now, if you look at the definition for DataRow, you'll notice that it doesn't implement IDisposable (or anything for that matter), doesn't have a finalizer, etc. It does, however, have a dependency on the table (which it gets via the DataRowBuilder passed in the constructor). Normally in that sort of situation, you never want to call dispose on an owning object until absolutely no one needs it anymore, as it could result in side effects from that parent reference being disposed of already.

However, in this case calling dispose doesn't actually do anything and it doesn't matter either way. In fact, you're calling Dispose as a premature optimization that has little or no effect, so it's superfluous. Your DataRows and the data they contain will be unaffected by calling dispose on the table.

(Sorry but not sorry the example is C# and not VB.NET, but there is no difference between the two in this example, except one is uglier than the other ;p )

var table = new DataTable();

table.RowDeleting += (sender, e) => {
     Console.WriteLine("Deleting");
};
table.Clear();
table.Columns.Add("Foo");
table.Columns.Add("Bar");

var row = table.NewRow();
row["Foo"] = "Hello";
row["Bar"] = "World";
table.Rows.Add(row);

table.Dispose(); // "Dispose call! We've got a Dispose call here!"

row.Delete(); // "See? No one cares."

I don't know what constitutes as authoritative enough for production code, but there you go.

Upvotes: 3

vermyx
vermyx

Reputation: 29

the data table will never get garbage collected. Dotnet will compile your code to keep that grid until the array is no longer referencing said row. The typical scenario I have seen is that until the parent object that created the grid and the array gets disposed of, the grid will stay around in the process marked for deletion but never garbage collected because it has a pending reference.

In other words, avoid doing it because typically it won't properly garbage collect the grid until the app is closed.

If it is unmanaged code it should blow up on first reference after dispose.

Upvotes: -2

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