Re: Infinite Recursion and other odd errors with Network API wrapper - C# Discussion Boards

Re: Infinite Recursion and other odd errors with Network API wrapper

6-Dec-03 22:11

One word: Paragraphs!

I think (without reading your post) the problem is, that you cant write to the Console form another thread.

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

Heath Stewart7-Dec-03 4:24

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 4:24

I'm with leppie on this one - use paragraphs next time. It's very difficult to follow your problem.

Since I can't really distinguish what you're problem is, let me give you a lesson or two on the .NET Framework. The GC only collects objects to which no references exist. If something is referencing an object in memory, it will NOT be GC'd. As far as your wrapper class for the Network API, all the methods you P/Invoked are static, which means they are methods of the Type - not an instance - so it can't be GC'd. If you get back a handle from one of those methods and aren't storing it (hence, not making a reference to it in your instance), then it will be GC'd.

-----BEGIN GEEK CODE BLOCK-----
Version: 3.21
GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
-----END GEEK CODE BLOCK-----

bri189a7-Dec-03 10:33

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 10:33

I'll try to clarify...

I made a set of classes that make interface with the WOpenEnum, WCloseEnum, and WEnumResources API functions simpiler. In that set of classes I also have a public class called Network that has static methods for retrieving the domains, servers, or shared folders in a network using the three API above (GetDomains(), GetServers(string domain), GetSharedFolders(string server). This set of classes also has three public structs (Domain, Server, SharedFolder) that I use for returning the information gathered in the three functions above. If you've worked with those three API before you know there are 8 items of information that come back, but only two that are important to the user, the 'Remote Name' and the 'Comment', this is what I put in those structs.

Now in a seperate project I make a reference to those set of class (which I just call EnumNetwork.dll)... With just a simple console project I can put it in a loop (normally wouldn't do this, nor use goto) as the following:

Start:
Server [] myServers = Network.GetServers("myDomain");
foreach(Server s in myServers)
{
Console.WriteLine(s.Name); //write the name of the server
}
goto Start:

And with this the servers will scroll out the console window forever without a glitch.

Now in a Windows Form I have a ListView object to make things look what users are use too... assume I already have a computer icon set for the second parameter of Item.Add below (the 0):

Server [] myServers = Network.GetServers("myDomain");
this.lstView.BeginUpdate();
this.lstView.Items.Clear();
foreach(Server s in myServers)
{
this.lstView.Items.Add(s.Name, 0);
}
this.lstView.EndUpdate();

What happens with this is that occasionally when closing the window itself you get 'Null Reference in mscrolib', or 'object not set to a reference of an object in unknown module'... and if running this code more that once in a 10 second period, or if there are many servers you get 'Infinite Recursion' and and 'Unhandled exception in sscrolib'...

Now I don't know what you mean by paragraphs unless you were saying I need to type better... in which case sorry for that... otherwise I'm ignorant to the meaning... but what I'm getting at is calling that method in the console window constantly results in no errors... over hours (yes I tested it for that long)... yet calling it in a method on a form results in unpredicatable errors... and try...catch statements don't do anything because the errors are caused in the Application.Run line... like I said, if you need the source code... not a problem... I'll email... thanks for any help, and thanks for the good info on the GC...

Brian

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

Heath Stewart7-Dec-03 10:41

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 10:41

Structs are not reference types - they are values types. If you think that different classes have reference to the same struct, you'd be wrong. They each have a separate copy of the struct because it is, once again, a value type.

This might have something to do with the ListView you're using, too. Since the ListViewItem is representing something that is getting destroyed by the GC (once structs are out of scope and the GC has a slice of time it cleans them out - including the values in the struct). Instead, when adding the s.Name to the list, use s.Name.Clone().ToString(). A copy of the string will be used instead of the string itself - which will get destroyed by the GC and a string is a reference type. This might be your problem.

bri189a7-Dec-03 11:08

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 11:08

Thanks again for you response...

Clone(), CopyTo(), and Copy() all tried and all have the same problem... I would be glad to send you the source code if you think you'd have time to look over it. As I've said I'm not the most experienced... everyday I'm learning, so if you want to tear my code apart and tell me I'm an idoit... I'm fine with that Smile | :)

... otherwise any other ideas would be more than welcome.
Brian

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

Heath Stewart7-Dec-03 11:12

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 11:12

You didn't mention that you were getting a NullReferenceException when using the field - only when you closed the application. The solution to this is simple - and is necessary in any good application - error handling! If you're not sure about input (and never trust user input for that matter!), always check to see if something is null (only reference types can be null, so a string can be). Instead, change your loop to something like:

foreach (Server s in servers)
{
  if (s != null && s.Name != null)
    this.listView.Items.Add(s.Name);
}

Likewise, you should always include exception handling in your code - especially when you can trust a source or that an object you didn't instantiate (like a parameter) isn't null. Always check your inputs, never trust user input (validate!), and always make sure that errors / exceptions are handled gracefully and - if possible - recovered. This is key in every programming language / framework.

bri189a7-Dec-03 11:46

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 11:46

Actually I do have that check in my code already:

if(myServers!=null)
{
foreach(Server s in myServers)
{
if(s.Name!=null)
{
this.lstViewNetwork.Items.Add(s.Name.Clone().ToString(), 0);
}
}
}

This is the most common error and the one you mentioned:

An unhandled exception of type 'System.NullReferenceException' occurred in system.windows.forms.dll Additional information: Object reference not set to an instance of an object.

When hitting break it goes to assembly... not a line of code as you normally get with null reference... when it does have the mscrolib error it get the green arrow break (don't know what the differance between that and the yellow is) but that is in the '}' underneath application.run(form)

Like I said, I'll send you the code if you have the time to look it.

Thanks again
Brian

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

bri189a7-Dec-03 13:10

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 13:10

Here is the code for the struct I use in the example:

<br />
public struct Server<br />
	{<br />
		private string n, c;<br />
		public string Name<br />
		{<br />
			get { return n; }<br />
			set { n = value; }<br />
		}<br />
		public string Comment<br />
		{<br />
			get { return c; }<br />
			set { c = value; }<br />
		}<br />
		public Server(string name, string comment)<br />
		{<br />
			n = name;<br />
			c = comment;<br />
		}<br />
	}<br />

Here is the code for the GetServers function, this function is part of the public class Network(), the dotNet_OpenEnum, dotNet_CloseEnum, and dotNet_EnumResources are static functions in a wrapper class for each of the API network functions... I did this versus calling the external function directly, the Flags class is simply const int's for various flags used when using the API network functions:

<br />
public static Server[] GetServers(string domainName)<br />
		{<br />
			int ret;<br />
			IntPtr ptrBuffer;<br />
			IntPtr ptrHandle = new IntPtr();<br />
			int BufferSize = short.MaxValue;<br />
			int NumberRequested = -1;<br />
			NETRESOURCE objNR = new NETRESOURCE();<br />
			objNR.lpRemoteName = domainName;<br />
			object obj = (object) objNR;<br />
			if(obj==null)<br />
			{<br />
				//something went wrong or there isn't a network available<br />
				return null;<br />
			}<br />
			//Open Main Handle<br />
			ret = dotNet_WNetOpenEnum.Execute(Flags.RESOURCE_GLOBALNET, Flags.RESOURCETYPE_ANY, Flags.RESOURCEUSAGE_ALL, obj, out ptrHandle);<br />
			//Check the results<br />
			if(ret!=0)<br />
			{<br />
				if(ptrHandle!=IntPtr.Zero) //close the handle if one was returned<br />
				{<br />
					ret = dotNet_WNetCloseEnum.Execute(ptrHandle);<br />
				}<br />
				return null;<br />
			}<br />
			//Enum Resources<br />
			ret = 234;<br />
			ptrBuffer = Marshal.AllocHGlobal(0);<br />
			//234=MORE_DATA_AVAILABLE, 487=ERROR_INVALID ADDRESS (EXPECTED)<br />
			while(ret==234 || ret==487)  //dynamically allocating memory!<br />
			{<br />
				NumberRequested=-1;<br />
				ret = dotNet_WNetEnumResource.Execute(ptrHandle, ref NumberRequested, ptrBuffer, ref BufferSize);<br />
				if(ret!=0)<br />
				{<br />
					Marshal.FreeHGlobal(ptrBuffer);<br />
					BufferSize*=2;	//because we found the dynamic allocation<br />
					//falls a little short on longer lists;<br />
					ptrBuffer = Marshal.AllocHGlobal(BufferSize);<br />
				}<br />
			}<br />
			//Check the results<br />
			if((ret!=0) || (NumberRequested < 1))<br />
			{<br />
				if(ptrBuffer!=IntPtr.Zero)<br />
					Marshal.FreeHGlobal(ptrBuffer);	//free the memory we allocated<br />
				if(ptrHandle!=IntPtr.Zero) //close the handle if one was returned<br />
				{<br />
					ret = dotNet_WNetCloseEnum.Execute(ptrHandle);<br />
				}<br />
				return null;<br />
			}		<br />
			//Determine what to do for returned results<br />
			Server [] servers = new Server[NumberRequested];<br />
			//Set a pointer for the buffer movement<br />
			int PtrMovement;<br />
			NETRESOURCE nr;<br />
			PtrMovement = ptrBuffer.ToInt32();<br />
			for(int n=0;n<NumberRequested;n++)<br />
			{	<br />
				//Set a pointer for the buffer movement<br />
				//Declare a NETRESOURCE class and convert our pointer to it<br />
				nr = (NETRESOURCE) Marshal.PtrToStructure(new IntPtr(PtrMovement), typeof(NETRESOURCE));<br />
				//Build the return;<br />
				servers[n] = new Server(nr.lpRemoteName, nr.lpComment);<br />
				//bump up the pointer;<br />
				PtrMovement += Marshal.SizeOf(typeof(NETRESOURCE));<br />
			}<br />
			Marshal.FreeHGlobal(ptrBuffer);	//free the memory we allocated<br />
			//close the handle if one was returned;<br />
			ret = dotNet_WNetCloseEnum.Execute(ptrHandle);<br />
			//return the NETRESOURCE class;<br />
			return servers;<br />
		}<br />

Thanks for any help!

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

bri189a7-Dec-03 18:30

Re: Infinite Recursion and other odd errors with Network API wrapper

7-Dec-03 18:30

Heath -

So I took out all of the additions we made and put it back to square one and at the bottom of the function I added GC.Collect():

<br />
                        string domain="Domain1";<br />
			this.lstViewNetwork.Items.Clear();<br />
			Server [] myServers;<br />
			myServers = Network.GetServers(domain);<br />
			this.lstViewNetwork.BeginUpdate();<br />
			if(myServers!=null)<br />
			{<br />
				foreach(Server s in myServers)<br />
				{<br />
					if(s.Name!=null)<br />
					{<br />
						this.lstViewNetwork.Items.Add(s.Name, 0);<br />
					}<br />
				}<br />
			}<br />
			count++;<br />
			this.lstViewNetwork.EndUpdate();<br />
			this.lblRefresh.Text = count.ToString();<br />
			GC.Collect();<br />
		}<br />

Now I know longer get errors, and everything is working perfectly (... some weird things still happen, when the screen saver started the form became the screen saver... weird... and once I got an error on closing the form, but after several attempts to get it to happen I haven't been able to, and something similiar when losing and regain focus to the form, it can now go throughs several thousand iterations before either of these errors happen whereas before we couldn't go more than 150. I'm not sure why GC.Collect() has made the error go away, but I know a 'fix to the problem' and 'fixing the problem' are two seperate worlds, and I was hoping maybe with this information and the other information I've given since your last reply will set some bells off in your head... any ideas?

Thanks again for all your help with this.
Brian

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

Heath Stewart8-Dec-03 2:13

Re: Infinite Recursion and other odd errors with Network API wrapper

8-Dec-03 2:13

Are you executing this method in a separate thread? If so, you must make all UI updates on the main UI thread. See Control.InvokeRequired and Control.Invoke for more information. Basically, you invoke your method (using a delegate with a matching signature to this.lstViewNetwork.Items.Add(s.Name, 0) and call Control.Invoke on that. This can cause similar problems to what you're seeing if you do add items on a separate thread. This is just the way Windows works (and most other window managers that I'm familiar with).

bri189a8-Dec-03 10:58

Deployment problem with the MS Web Browser Control

8-Dec-03 10:58

Heath,

Thanks again for all your help, I solved it. I am flawless now... it wasn't what we were expecting... it was something really stupid - something we looked over. I was over-allocating memory in my function - apparently when you send to much memory to WNetEnumResources it fills the rest of the memory with items, then when calling it again your not getting the new memory, but the remainder of the old, and the new memory for the new objects is pushed up the stack - I know that's a terrible explination but it appears that is what was happening. Now that I'm allocating it correctly I have no problems whatsoever in any context... console or form and I have reloaded my ListView control every second for over an hour with simple .Add(s.Name) and not so much as a flicker.

I wanted to thank you once again for you help along the way. I learned a lot on this one... if you ever want a copy, please email me.

Brian

If you ever meet somebody who says they know it all, they are obviously ignorant and probably write terrible code.

Furty6-Dec-03 14:42

Furty

6-Dec-03 14:42

We have an issue with using the IE ActiveX control where about 1 in 20 users are expriencing total system lockup when our application loads.

The application is being deployed with the following files:

AxInterop.SHDocVw.dll
Interop.SHDocVw.dll
partial.mshtml.dll

The partial.mshtml.dll file comes from SharpReader[^], and by all accounts fixed their deployment problems, which are similar to our own.

I have extensive trace output in the app, and can verify that the point of lockup is when the web browser control is instantiated. Please note that I am navigating to about:blank in the constructor to ensure the control has a handle.

Has anyone else ran into similar problems deploying a C# app with the IE control? if so, any ideas?

Re: Deployment problem with the MS Web Browser Control

Heath Stewart7-Dec-03 4:18

Re: Deployment problem with the MS Web Browser Control

7-Dec-03 4:18

I doubt this would cause a lockup, but what versions of Internet Explorer are the 1 in 20 users using? If the partial.mshtml.dll was created with a newer version that those few users don't have, and you're trying to use those newer interfaces that don't exist in the MSHTML DOM, this would most likely cause a problem. Your installer should make sure they have the proper version (or higher) of IE.

Furty8-Dec-03 19:49

Furty

8-Dec-03 19:49

I am working closely with one affected user on the issue.

He is using Win98SE, with IE 6 SP1. I have added a bunch of trace output to the app, and the total system lockup is happening right after the ActiveX is instantiated, when the control would be receiving a handle I guess.

I've tried compiling the app for both 1.0 and 1.1 framework versions, and I've referenced & distributed the entire Microsoft.mshtml.dll assembly.

As for the control itself, I am only calling the Navigate method, and catching the OnNavigateComplete2 event - nothing else.

Note that I have 26 other people using the app with Win98 + IE 5-6 without problem, but this one fellow is experiencing lockups on both of his Win98 SE systems. Outside of him, who knows how many people have dismissed the app as inoperable and simply not advised me!

Re: Deployment problem with the MS Web Browser Control

Heath Stewart9-Dec-03 2:37

Re: Deployment problem with the MS Web Browser Control

9-Dec-03 2:37

Man, I don't know. Confused | :confused:

How much memory does this person have in his machines? I mean, the .NET Framework would throw an exception and exhausting the memory wouldn't lock up the system, but it might appear that way. I doubt this is the problem, though.

Have you checked the MS KB? Besides that, all I can think to tell you is to post a message to an appropriate MS newsgroup (msnews.microsoft.com), but I doubt that'll help since replies to more advanced or "odd" problems like this almost never get answered.

Furty9-Dec-03 11:43

Furty

9-Dec-03 11:43

Heath Stewart wrote:
How much memory does this person have in his machines?

One has 64MB, the other 128MB, however my low-end test machine (that runs the app fine) has just 56MB usable RAM (8 MB is taken up by the video card).

Heath Stewart wrote:
Have you checked the MS KB?

Yes. The only possibly related article I could find was a COM import bug in fx 1.0 that was fixed in 1.0 SP1. However, compiling the app for fx 1.1 should have worked around this issue if it was the problem.

Heath Stewart wrote:
Besides that, all I can think to tell you is to post a message to an appropriate MS newsgroup

Have now posted the problem to microsoft.public.dotnet.framework, but as you noted and I've personally experienced, difficult questions seem to get lost in the ether...

Thanks for your help anyway Heath

Exception in File explore

naxos6-Dec-03 13:24

naxos

6-Dec-03 13:24

Hey

I´m trying to make a File Explore like windows explore. I get the Logical drives GetLogicalDrives and then iterate through them. At this point I´m using GetDirectories.
My problem is that I want to show all the drives, also if there is no media like a cdrom or floppy. But using GetDirectories on a:\ with no floppy inserted throws an exception I can't catch.
Please help I want to avoid this.

Re: Exception in File explore

leppie6-Dec-03 22:15

Application in Batch Mode with user interface

6-Dec-03 22:15

naxos wrote:
But using GetDirectories on a:\ with no floppy inserted throws an exception I can't catch.

I somehow doubt this.

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

Patrick Luijpers6-Dec-03 12:26

Patrick Luijpers

6-Dec-03 12:26

I am trying to create an manual and automatic application in one with windows interface. The manual/automatic switch is in a configuration file.

I have created a form with two buttons. Start and Cancel/Exit. The Start button starts a process that can take up to an hour. The cancel button cancels the process and Exit closes the application.
So far no problem.

When the application is in automatic mode. It should start the process and exit the application. (batch mode), BUT I want the form to show the processing information. Just in case the operator is watching.

Thanks for your help.

Patrick

Re: Application in Batch Mode with user interface

leppie6-Dec-03 22:16

Re: Application in Batch Mode with user interface

6-Dec-03 22:16

So what is the problem?

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

Patrick Luijpers7-Dec-03 5:17

Patrick Luijpers

7-Dec-03 5:17

The problem is that the form does not show while running the automatic processes.

For automatic I put Start1, Start2 and Exit in Initialize(), which are the same routines the buttons call in manual mode.

-P

Re: Application in Batch Mode with user interface

leppie7-Dec-03 5:25

Some nodes in TreeView with checkboxes and some others without. Is it possible?

7-Dec-03 5:25

Patrick Luijpers wrote:
The problem is that the form does not show while running the automatic processes.

I assume you mean the form is not responding, due to the process taken a long while.

Just fire the process off in a new thread. Smile | :)

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

TomaHawKPT6-Dec-03 12:18

TomaHawKPT

6-Dec-03 12:18

Hi,

I'd like to know if it's possible to have a TreeView where some nodes have checkboxes and some other nodes don't.

And if it is possible, how can I do it..

Thanks in advance,
TomaHawK

Re: Some nodes in TreeView with checkboxes and some others without. Is it possible?

Heath Stewart7-Dec-03 4:13