2008-06-27

Memory leaks

As a follow up to yesterday's post here is a list of problems I found...

01: The following code for some reason causes the form holding the DirtyObjectCatcher to remain referenced.


if (Owner.MdiParent != null)
{
Owner.MdiParent.Activated += new EventHandler(MdiParent_Activated);
Owner.MdiParent.MdiChildActivate += new EventHandler(MdiParent_MdiChildActivate);
}
The odd thing about this is that it really is the events that matter! I subscribe Shown, Disposed, Activated on the Owner (which is a form) and that doesn't cause the same behaviour. The reason is that the Owner normally gets disposed and takes out the DirtyObjectCatcher with it, however, if I have Owner.MdiParent events referencing DirtyObjectCatcher then the form will never get disposed because DirtyObjectCatcher has a strong reference to Owner. Maybe I should change it, but for now the Shown and Activated events seem to be doing the trick.

02: This one was a real pain! DirtyObjectCatcher creates its own UndoBlock and then subscribes to it, so that whenever the user modifies an object it goes into the UndoBlock and the catcher is notified. At this point other components (such as ObjectValidator) can get a list of modified objects and do something (such as evaluate their OCL constraints).

Unfortunately this event fires at some point between the user making the change and the ECO cache being ready for the new value to be read. For this reason in the past I had to set

Application.Idle += CheckForModifiedObjects;

CheckForModifiedObjects would then trigger the relevant events in Application's Idle event so that we know the changes to the ECO cache are ready to be read. Unfortunately I made a silly mistake, I forgot to do this as the first line of CheckForModifiedObjects

Application.Idle -= CheckForModifiedObjects;

As a result the static Application class had a reference to my DirtyObjectCatcher via an event. DirtyObjectCatcher holds a reference to the form (Owner) and the EcoSpace (ServiceProvider). So the form and the EcoSpace would remain in memory.

03: In the past you could not subscribe to UndoBlock so I had to subscribe to DirtyListService. Unfortunately this would not get triggered if you activated a DirtyObjectCatcher on an object that was already dirty, or transient. To overcome this I added a CheckForUpdates method which would get every instance of DirtyObjectCatcher to check its UndoBlock for changes.

The idea was that you plug into the ECO cache and call the static DirtyObjectCatcher.CheckForUpdates whenever something changed. A pain in the ass. I requested UndoBlock.Subscribe and it was implemented within days (thanks Jonas!) but I left that code in just in case anyone was using it. Unfortunately this meant I had a static List sitting around holding references to my DirtyObjectCatchers. Again this referenced the EcoSpace and the Form, so the Form was never disposed in order to dispose of my DirtyObjectCatcher.

This wasn't noticed for some time because I use the AutoFormService to handle the lifetime of my forms, but my current app has quite a few forms where I manage the lifetime manually so the form wasn't automatically being disposed as I had expected. In addition the Form class does not call Dispose on any of its components when you call its Dispose method, which I find very strange!

Anyway, that's the lot. What a hellish week! I have uploaded the lastest version of EcoExtensions here:

www.peterlesliemorris.com/blogfiles/ecoextensions.zip

DirtyObjectCatcher

Oh boy, what a nightmare! After days of messing around I finally found where the memory leak is in my app, it was in DirtyObjectCatcher!

The DirtyObjectCatcher used to subscribe to the DirtyListService, so that it was notified whenever an object was made dirty. I experienced this problem...

01: User creates a "Call" to a customer site.
02: User edits a purchase order.
03: Save purchase order (merges the undo block to the Call undo block and closes the form)
04: Edit the purchase order again from the Call form

The PurchaseOrder is already dirty so it wont get triggered again, this used to result in no constraints being checked etc and the possibility of entering dodgy data. The solution at the time was to have a static list in DirtyObjectCatcher

private List Instances;

whenever a new instance was created it would be added, whenever Dispose was called it would be removed. I then hooked into the cache chain and whenever a value changed I would call a static method on DirtyObjectCatcher which iterated over Instances and told each to check if anything had changed. It worked fine enough, and I put in a request to add a Subscribe method to IUndoBlock.

My request for IUndoBlock.Subscribe was soon added so I changed the code. Now it worked lovely! Unfortunately there was a problem! I had left the static code in the component just in case anyone was using it, I should really have just removed it as it is now obsolete. The really big problem however was that I had never added a Finalizer to the DirtyObjectCatcher class to call Dispose(). I had assumed the following in the Windows.Form default code template would call Dispose.



private System.ComponentModel.IContainer components = null;
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}



However I was wrong. The components on the form are never added to this "components" member. As a result the Instances list grew and grew, and was never emptied. DirtyObjectCatcher holds a reference to the EcoSpace, so this is why the memory usage got bigger and bigger! I was going to add the Finalizer and remove the instance from Instances, but I have decided to remove Instances completely!

Update: There were some other odd issues too which I will blog about tomorrow after I have released an update!

2008-06-25

TeamCoherence - disaster!

That's it, my short evaluation of TC is over!

Problem 1: I emailed support with a question weeks ago, didn't get a response. Not impressed.

Problem 2: I reinstalled my O/S recently so had to restore my version control folder. When I try to check files out I now get an "Object not found" error, whatever that means? Some searching reveals it is a bug that has been fixed in the version I have, I beg to differ.

Problem 3: This one was the worst! I use TC client for a customer already which is why I decided to try out the server. I connected to the customer server, checked out loads of files, upgraded my VS2005 project to VS2008 and then checked everything back in. What a disaster! TC had replaced the source in the customer files with source from my private local server!

I couldn't believe it! As I looked through Assembly.cs files I could see WinForm code from the last project I worked on locally! This is obviously bad because I had exposed source code from one concerned party to another. Luckily it was my own source code and I trust the person I exposed it to, but that could have landed me in legal trouble if there had been NDA's involved!

Also, there didn't seem to be a way to undo all changes in check-in number X. I had to find each file with a change containing the text "VS2008" and delete the revision manually. This was made worse by the fact that the F3 search in TC doesn't take you to the next found item but instead takes you to the first found item after the current folder! So, I spent quite a bit of my day yesterday scanning through hundreds of files and manually deleting revisions from a single check-in.

I am actually shaking my head as I write this, I just can't believe it!

2008-06-16

TimeBasedSyncHandler

I recently had to tweak my remote persistence server settings. I noticed that I had leaft the SyncHandler.HistoryLength at the default value of 10,000 items. This was overkill because my clients sync every 3 seconds. I thought maybe I should drop this down to about 100, that should be okay? Each client only does about one update every few minutes so I it should, right?

Problem is not all of my users are people. One user is a messenger service which looks for unsent messages, sends them one at a time, marking each in turn as sent and updating the database. This gets run every five minutes so probably sends about fifty messages at the most, but what if someone decides to change it to ten minutes, or thirty? So maybe I should increase the HistoryLength to about 200?

Then there is the other client, this one syncs with an external database. This could perform hundreds of updates every minute. If the messenger is set to run every thirty minutes...I'm not sure what a good HistoryLength would be! If I set it too low I fill it up quickly and my clients will have to deactivate/reactivate their EcoSpace instances. If I set it too high I might use up too much memory, especially if the messenger runs infrequently and the history gets filled up with "human" client updates which are much larger.

So, I wrote my own SyncHandler. This one accepts a TimeSpan property, which by default is five minutes but on my server I dropped it to two minutes (forty times longer than my clients' sync intervals.) The idea is that I keep changes for the specified period of time no matter how irregularly the updates occur. This way the server uses more memory during heavy usage but

A: Usage drops during lower activity, in fact it goes right down if there are no updates for the specified TimeSpan.
B: It wont run out of history length too quickly for the client.

If you'd like to try it for yourself take a look here.

2008-06-11

Making a generic type from a Type

List<Person> p = new List<Person>();

This works fine, but what about this?

Type someType = typeof(Person);
List<someType> p = new List<someType>();

Nope!

But you can do this...

Type genericType = typeof(List<>).MakeGenericType(someType);

Why would I want to? Because I am creating a tool that generates plain old .NET objects from an EcoSpace's model, and I wanted to implement multi-role association ends as

public List<Building> RoleName;

rather than just

public Building[] RoleName;

Returning a binary respose in ASP MVC RC3

In a previous post I showed how to return a binary file from a controller action, well, this no longer works in release candidate 3 of the framework. Instead you have to create a new ActionResult descendant to do the job for you. This is how I did it....

return new BinaryResult(data, Path.GetFileName(productFileName));


and the class is implemented like so:

public class BinaryResult : ActionResult
{
private string ClientFileName;
private byte[] Data;
private string VirtualFileName;

public BinaryResult(string virtualFileName, string clientFileName)
{
if (string.IsNullOrEmpty(virtualFileName))
throw new ArgumentNullException("VirtualFileName");
if (string.IsNullOrEmpty(clientFileName))
throw new ArgumentNullException("ClientFileName");

ClientFileName = clientFileName;
VirtualFileName = virtualFileName;
}

public BinaryResult(byte[] data, string clientFileName)
{
if (data == null)
throw new ArgumentNullException("Data");
if (string.IsNullOrEmpty(clientFileName))
throw new ArgumentNullException("ClientFileName");

ClientFileName = clientFileName;
Data = data;
}

public override void ExecuteResult(ControllerContext context)
{
if (!string.IsNullOrEmpty(VirtualFileName))
{
string localFileName = context.HttpContext.Server.MapPath(VirtualFileName);
FileStream fileStream = new FileStream(localFileName, FileMode.Open, FileAccess.Read, FileShare.Read);
using (fileStream)
{
Data = new byte[fileStream.Length];
fileStream.Read(Data, 0, (int)fileStream.Length);
}//using fileStream
}

context.HttpContext.Response.AddHeader("content-disposition", "attachment; filename=" + ClientFileName);
context.HttpContext.Response.BinaryWrite(Data);
}
}

2008-05-29

ASP MVC preview 3 released

I'm trying to upgrade from Preview 2 to Preview 3. I think the idea of having each action return an ActionResult was a good one, so far it has actually made my code slightly smaller.

What I don't understand though is why Html.Select seems to have disappeared...

Compilation Error
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS1501: No overload for method 'Select' takes '5' arguments

Source Error:

Line 8: Product
Line 9:
Line 10: <%= Html.Select("SoftwareID", (object)ViewData["SoftwareList"], "Name", "ID", (object)ViewData["SoftwareID"]) %>
Line 11:
Line 12:


When I go into the APX and type Html. there is no Select method listed along with the other options! Where is it?