Removing items from list while performing operations on it - C# Discussion Boards

Re: Treeview aftercheck

Wannes Geysen29-Mar-10 21:25

Wannes Geysen

29-Mar-10 21:25

thanks for the help

Get list of groups for a given user using ActiveDirectory

QuickDeveloper29-Mar-10 2:18

QuickDeveloper

29-Mar-10 2:18

Hi
I am getting the list of groups for a particular user using ActiveDirectory.
I am using the following code.

void GetUserDetailsFromAD()
{
  string _userName = Environment.UserName;
  string _userDomain = Environment.UserDomainName;

//Use given URL
   using (DirectoryEntry de = new DirectoryEntry(string.Format("LDAP://URL /OU=XYZ,DC={0},DC=XYZ,DC=XYZ,DC=com",_userDomain)))
            {
                   //Create a text file to write details
                    TextWriter tw = new StreamWriter("C:\\LDAP.txt");

                    de.AuthenticationType = AuthenticationTypes.Secure |AuthenticationTypes.ReadonlyServer;
                    using (DirectorySearcher search = new DirectorySearcher(de))
                    {
                        search.Filter = "(sAMAccountName=" + _userName + ")";
                        search.PropertiesToLoad.Add("displayName");
                        search.PropertiesToLoad.Add("memberof");
                        SearchResult result = search.FindOne();


                        if (result != null)
                        {
                            _displayName = result.Properties["displayname"][0].ToString();

                            //Loop through all the groups that user is part of
                            foreach (object item in result.Properties["memberof"])
                            {

                                 //Write the groups to a text file
                                tw.WriteLine(item.ToString());

                              //Check whether the group in which user is present starts with ABC
                                if (item.ToString().StartsWith("CN=ABC,DC=DEF"))
				{
					//user is member of ABC group
				}
				else
				{
				       //user is not member
				}
                            }
                        } 
                    }

                    tw.Close();
               
              
            }
}

When i run these program from my local machine(let's say machine A) ,the list of groups which _userName belongs to is populated in C:\\LDAP.txt file.However if i run this from another machine (machine B) in same network,only some groups are displayed ,not all.Eg:If machine A lists group 1,2,3,4 ,machine B lists only 1,2.

1)How can i know whether there are any restrictions in place on other system?(due to which all groups are not displayed)
2)How to check whether there any changes in network settings in the second machine with respect to Active Directory?

Please suggest.

"Every morning I go through Forbes list of 40 richest people in the world. If my name is not in there, I go to work..!!!"

Re: Get list of groups for a given user using ActiveDirectory

Abhinav S29-Mar-10 4:05

Abhinav S

29-Mar-10 4:05

This[^] might provide some assistance.

Me, I'm dishonest. And a dishonest man you can always trust to be dishonest.
Honestly. It's the honest ones you want to watch out for...

Automatic Server Shutdown

FJJCENTU29-Mar-10 0:18

FJJCENTU

29-Mar-10 0:18

I would like that my Server (Windows 2003) automaticly shutdown at 20.00 and for it I think that the Best solution is to create a Net C# Windows Service, but could anybody tell me the C# command for getting the system down, I know that inside the Operating System the order is ShutDown but how to access the Operative System from inside the C# code, not existing shell orders as in older languages.

Best Regards

Re: Automatic Server Shutdown

DaveyM6929-Mar-10 0:48

DaveyM69

29-Mar-10 0:48

There are several alternatives on this SO thread[^].

Dave

If this helped, please vote & accept answer!

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Re: Automatic Server Shutdown

David Skelly29-Mar-10 1:56

David Skelly

29-Mar-10 1:56

This may be a dumb question from me but why can't you just use the Task Scheduler to schedule a shutdown at the required time?

Re: Automatic Server Shutdown

Dave Kreskowiak29-Mar-10 3:43

Dave Kreskowiak

29-Mar-10 3:43

Why would you need to write any code at all since you can just put a SHUTDOWN command line in a Scheduled Task job?

Open a CMD prompt and type shutdown /? for the command line options.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008
But no longer in 2009...

Removing items from list while performing operations on it

xkrja29-Mar-10 0:17

xkrja

29-Mar-10 0:17

I would like to know what happens if objects are removed from a list while operations are performed on this list?

Let's say we have this class:

class MyListObject
{
int MyInt {get;set;}
string MyString {get;set;}
}

And we have a list of "MyListObject" called "MyList". We also have an eventhandler that can trigger randomly. In that eventhandler a random item in "MyList" is removed from "MyList".

Now, what happens if I do something like:

MyList.Find(delegate (MyListObject mlo) {return mlo.MyString == "hello";});

And at the same time we perform this operation on the list the event is triggered and the eventhandler removes some item from the list. Will that throw some kind of exception? I don't know how to test it so that's why I'm asking you guys.

If this can cause problems, how can I get around this?

Thanks for help!

Re: Removing items from list while performing operations on it

Keith Barrow29-Mar-10 0:47

Keith Barrow

29-Mar-10 0:47

You get a System.InvalidOperationException exception with the message "Collection was modified; enumeration operation may not execute.".

To fix:

lock (MyList)
{
   MyList.Find(delegate (MyListObject mlo) {return mlo.MyString == "hello";});
}

This locks the object so that only the code block can modify / access it. If you put more than one lock around the object in different places, you need to think about race and deadlock conditions, but for your example it should be fine.

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Re: Removing items from list while performing operations on it

SeMartens29-Mar-10 0:48

SeMartens

29-Mar-10 0:48

Hi,

at MSDN it is written that the enumeration is not thread-safe:

http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx[^]

As far as I know removing an item from an collection that is enumerated at the moment throws an Exception (something like an InvalidOperationException). So to solve this problem I suggest using the lock statement:

http://msdn.microsoft.com/en-us/library/c5kehkcz%28VS.80%29.aspx[^]

Lock the access when removing something from the list, and lock when you iterate through the list. (Be sure to use the same lock-object!)

Hope this helps.

Regards
Sebastian

It's not a bug, it's a feature!

Check out my CodeProject article Permission-by-aspect.

Me in Softwareland.

using (SqlTransaction... )

Dewald29-Mar-10 0:12

Dewald

29-Mar-10 0:12

For much too long I have not used Transactions in my DB apps - let's not go into how stupid that is.

So I'm working on an existing app and trying to wrap Transactions around sequences of SqlCommands that I need to keep atomic. The approach I've followed thus far is something like:

SqlTransaction mySqlTransaction = mySqlConnection.BeginTransaction()
try
{
   // First SQL command that is part of an atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }

   // Second SQL command that is part of an atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }

   mySqlTransaction.Commit();
}
catch
{
   mySqlTransaction.Rollback();
}

Then, as I reached the halfway mark (as always happens), it occurred to me that, surely, you can wrap the SqlTransaction in a using block as well. I can't seem to find thorough documentation on how to do that though. Could someone help out perhaps?

If you put your SqlTransaction in a using block, when is it committed? What happens if an exception occurs? Will it automatically roll back?

Re: using (SqlTransaction... )

Eddy Vluggen29-Mar-10 1:06

Eddy Vluggen

29-Mar-10 1:06

Dewald wrote:
If you put your SqlTransaction in a using block, when is it committed?

On the "mySqlTransaction.Commit()" statement.

Dewald wrote:
What happens if an exception occurs?

The catch-block is executed, doing a rollback. This might cause an InvalidOperationException if the connection is already closed or rolled back. (Source: MSDN[^])

Dewald wrote:
Will it automatically roll back?

Yup, because you called "Rollback". Shouldn't be a problem if that fails, because there's no commit called - and thus the data shouldn't be saved even if you fail to rollback the transaction.

I are Troll Suspicious | :suss:

Re: using (SqlTransaction... )

Keith Barrow29-Mar-10 1:07

Keith Barrow

29-Mar-10 1:07

The following snippet should help:

using (SqlConnection cn = new SqlConnection()) 
using (SqlTransaction tr = cn.BeginTransaction())      
{ 
      //some code 
      tr.Commit(); 
}

Note that if the transaction is not committed, calling dispose on the SqlTransaction object rolls-back automatically.

Re: using (SqlTransaction... )

PSK_29-Mar-10 1:08

PSK_

29-Mar-10 1:08

You should be using it through using block like following

  using (SqlTransaction mySqlTransaction = mySqlConnection.BeginTransaction())
{
    // First SQL command that is part of an atomic transaction
    using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
    {
        mySqlCommand.ExecuteScalar(); // or whatever
    }   // Second SQL command that is part of an atomic transaction
    using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
    {
        mySqlCommand.ExecuteScalar(); // or whatever
    }
    mySqlTransaction.Commit();
}

Using block implements try-catch-finally internally, so your transaction will be rolled backed automatically in case any exception occurs.

WWW, WCF, WWF, WPF, WFC .... WTF

Re: using (SqlTransaction... )

Dewald29-Mar-10 1:51

Dewald

29-Mar-10 1:51

Thanks for that. But now, does this mean I lose the usage of the transaction once I commit it? I mean, after the mySqlTransaction.Commit() statement but still inside the using block, can I start the transaction again or do I have to close the using block and open a new using block to start a new transaction?

Here is an analogy as implemented according to my original approach:

SqlTransaction mySqlTransaction = new;
try
{
   mySqlTransaction = mySqlConnection.BeginTransaction();
   // First SQL command that is part of an atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }

   // Second SQL command that is part of an atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }

   mySqlTransaction.Commit();

   // Now we do stuff during which we don't want to have the DB locked

   mySqlTransaction = mySqlConnection.BeginTransaction();
   // First SQL command that is part of another atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }

   // Second SQL command that is part of another atomic transaction
   using (SqlCommand sqlCommand = new SqlCommand("...", mySqlConnection, mySqlTransaction))
   {
      mySqlCommand.ExecuteScalar(); // or whatever
   }
}
catch
{
   mySqlTransaction.Rollback();
}

It's probably no big deal and if need be I can start a new using block for the second set of atomic SQL commands but in the application that I'm working on it will introduce some scope problems with local variables which I'd have to work around - and I'm a rather lazy programmer Smile | :)

Re: using (SqlTransaction... )

PSK_29-Mar-10 3:06

PSK_

29-Mar-10 3:06

Dewald wrote:
can I start the transaction again or do I have to close the using block and open a new using block to start a new transaction?

In that case you need to open a new using block for sure.

WWW, WCF, WWF, WPF, WFC .... WTF

Re: using (SqlTransaction... )

Dewald29-Mar-10 3:33

Dewald

29-Mar-10 3:33

OK thanks.

Re: using (SqlTransaction... )

PIEBALDconsult29-Mar-10 4:14

PIEBALDconsult

29-Mar-10 4:14

Yeah, what they said, but why keep creating Command instances? Why not create one and reuse it?

Re: using (SqlTransaction... )

Dewald29-Mar-10 21:27

Dewald

29-Mar-10 21:27

Sure, that's actually what I have been doing for the most part but I used separate ones for the example to emphasise them being separate commands forming part of one transaction.

Just to confirm though, does it mean that you can reuse a SqlCommand but not a SqlTransaction? If that is so, does it mean that, typically there would be nothing else inside your using SqlTransaction block after the sqlTransaction.Commit()?

And one last question, what is this "using" keyword called? In other words, what do I Google for, or look for in MSDN if I want to get information on this "using" as opposed to the using directive that precedes your namespaces at the top of your file?

Re: using (SqlTransaction... )

PIEBALDconsult30-Mar-10 4:27

PIEBALDconsult

30-Mar-10 4:27

Dewald wrote:
but not a SqlTransaction

That's my understanding.

Dewald wrote:
nothing else inside

Well, you might want to log something, it depends on what else you might want to do.

Dewald wrote:
what is this "using" keyword called?

I call it the using statement.

At any rate, I use try/catch; I don't use using with transactions, but that's just me.

How does CLR differentiates between value and reference types

Praveen Raghuvanshi28-Mar-10 23:00

Praveen Raghuvanshi

28-Mar-10 23:00

Hi,

Basic question to ask.
we know everything in .Net is derived from System.Object, even value and reference types.
So, how does CLR differentiate between the two and stores the value type on Stack and reference types on Heap?

In continuation to above, I have another query

we have a value type as

int age = 35;

and we have a class which contains both the value types and reference types as shown below

Class Company
{
	int employeeCount = 3000;
	Employee emp;

	Public Company(Employee emp)
	{
		this.emp = emp;
	}
}

and we created the object of Company class as shown below

Company cmpny = new Company(emp);

Question is where does the employeeCount will get stored(Stack or Heap) and Where does the cmpny gets stored?

Thanks in advance,

Praveen Raghuvanshi
Software Engineer,

India.

Re: How does CLR differentiates between value and reference types

PSK_28-Mar-10 23:52

PSK_

28-Mar-10 23:52

1- All the value types are derived from System.Valuetype and are stored in the stack. For other type of object needs to be initialized and are stored in the managed heap with all of its data members.

2- All the value type present in an object resides in managed heap together. They are not stored separately in the stack.

WWW, WCF, WWF, WPF, WFC .... WTF

Re: How does CLR differentiates between value and reference types

Keith Barrow29-Mar-10 0:06

Keith Barrow

29-Mar-10 0:06

Rags1512 wrote:
we know everything in .Net is derived from System.Object, even value and reference types.

All value types are derived implicitly from the System.ValueType, which is derived from object.

Rags1512 wrote:
Question is where does the employeeCount will get stored(Stack or Heap) and Where does the cmpny gets stored?

The answer is, where a value type is declares determines where it ends up. The cmpy object is stored in the heap, but with a pointer from the stack. employeeCount is stored in the heap memory, but is accessed [transparently] through a pointer on the stack.

Here is a good article on heap/stack allocation
http://www.c-sharpcorner.com/UploadFile/rmcochran/csharp_memory01122006130034PM/csharp_memory.aspx[^]

Though the author fudges the point about the cmpy pointer a little.

Re: How does CLR differentiates between value and reference types

Praveen Raghuvanshi29-Mar-10 1:39

Praveen Raghuvanshi

29-Mar-10 1:39

Appreciate the explanation provided,

Praveen Raghuvanshi
Software Engineer,

India.

Re: How does CLR differentiates between value and reference types

Gideon Engelberth29-Mar-10 2:55

Gideon Engelberth

29-Mar-10 2:55

Rags1512 wrote:
So, how does CLR differentiate between the two and stores the value type on Stack and reference types on Heap?

That value types are always on the stack and reference types are always on the heap is a common misconception. The distinction between value types and reference types is not where they are allocated (stack vs. heap), the difference is how they are passed to functions and assignment. Value types are passed by value. Reference types are passed by reference.

An article discussing this can be found here

Rags1512 wrote:
we know everything in .Net is derived from System.Object, even value and reference types.

Also, not quite true. See this article for a good explanation.

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