Re: Suggestion about a data structure - C# Discussion Boards

Luc Pattyn21-Oct-09 2:40

Luc Pattyn

21-Oct-09 2:40

Hi,

I would use a list, however I would keep it sorted on due time.
that way the timer's tick only has to check the first entry of the list.
Each time an alarm fires, it gets removed from position zero (which causes the list to shift).
So the only times the length of the list is relevant is when a new alarm is added, or an elapsed one is removed.

Smile | :)

Luc Pattyn

I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages

Local announcement (Antwerp region): Lange Wapper? 59.24% waren verstandig genoeg om NEEN te stemmen; bye bye viaduct.

Siddhartha S.21-Oct-09 2:45

Siddhartha S.

21-Oct-09 2:45

Thanks very much Luc for your answer but the sorting+processing of the list is to be done on everyalarm raise event. i.e every time an alarm is fired, I will have to sort the list and also remove the task. If i got ur your idea prioperly then the sorting of list will also have to be done whenever a new event is added.
If these operations take more than a minute then the calcualtions may go wrong.
How do you suggest a solution then?

Best Regards,
Sid

Luc Pattyn21-Oct-09 2:53

Luc Pattyn

21-Oct-09 2:53

Huh?
When an alarm fires, it is the first in the list; removing it does not require a re-sort.
Adding an alarm requires a sort. It would take millions of entries before a sort would take a minute to execute.

Smile | :)

Luc Pattyn

I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages

Local announcement (Antwerp region): Lange Wapper? 59.24% waren verstandig genoeg om NEEN te stemmen; bye bye viaduct.

Windows Identity of the currently logged in user

Siddhartha S.21-Oct-09 2:55

Siddhartha S.

21-Oct-09 2:55

Got the idea! Thanks Luc. Big Grin | :-D

Best Regards,
Sid

ramz_g20-Oct-09 22:23

Re: Windows Identity of the currently logged in user

20-Oct-09 22:23

Hi,
I have created an application which runs on a Web Server. This web server in-turn runs as a windows service.
This windows service's account is configured as follows

ServiceProcessInstaller serviceProcessInstaller = new ServiceProcessInstaller();

serviceProcessInstaller.Account = ServiceAccount.LocalSystem;

Now I have a scenario in which I have to access a database and execute queries in it which needs the currently logged in user. The problem is that whenever I try to use

System.Security.Principal.WindowsIdentity.GetCurrent().Name

I am getting the name as "SYSTEM" and not the logged in user's name. And I know that this is because the service is run at the system level.

I can change the ServiceAccount as

serviceProcessInstaller.Account = ServiceAccount.User

I can now get the currently logged in user name. But, this requires the user to enter his user name and password when the service is being installed and I do not want that to happen.

Hence is there any other way in which I can get the WindowsIdentity object of the currently logged in user? Please suggest..

Thanks,
ramz_g

stancrm20-Oct-09 22:31

stancrm

20-Oct-09 22:31

http://msdn.microsoft.com/en-us/library/system.environment.username.aspx[^]

Re: Windows Identity of the currently logged in user

ramz_g20-Oct-09 23:11

Re: Windows Identity of the currently logged in user

20-Oct-09 23:11

Hi stancrm,

Thanks for your reply.. But I have tried Environment.UserName already but it doesn't help, maybe because my service is running at the System level and the environment here is the System and not the user.

Also, I would like to know whether there is any class that actually returns me the Windows Identity object of a specified user.

Thanks,
ramz_g

Eddy Vluggen20-Oct-09 23:40

Eddy Vluggen

20-Oct-09 23:40

ramz_g wrote:
System.Security.Principal.WindowsIdentity.GetCurrent().Name

I am getting the name as "SYSTEM" and not the logged in user's name. And I know that this is because the service is run at the system level.

That's correct. Your service is running with the privileges of the system account.

ramz_g wrote:
I can now get the currently logged in user name. But, this requires the user to enter his user name and password when the service is being installed and I do not want that to happen.

It would be a breach in security if you could impersonate that user without them entering a password for their account. Either your database needs to grant access to the builtin system-account, or the service needs to run under it's own account, or you use the users' account.

If you're using SQL Server, then you might want to switch to a SQL-login (as compared to Windows Authentication). You wouldn't want to do that with the 'sa' user, but it would get you started Smile | :)

I are Troll Suspicious | :suss:

Re: Windows Identity of the currently logged in user

ramz_g21-Oct-09 2:05

Re: Windows Identity of the currently logged in user

21-Oct-09 2:05

Hi Eddy,
Thanks a lot for your reply..

Eddy Vluggen wrote:
It would be a breach in security if you could impersonate that user without them entering a password for their account.

Yes I understand that.

Eddy Vluggen wrote:
If you're using SQL Server, then you might want to switch to a SQL-login

No, I'm not using SQL Server. All I'm using is a simple Sqlite database and I'm using simple queries where I have to use the windows logged-in user name.

So, is there any way that I can obtain the logged in user name alone?

Thanks,
ramz_g

Eddy Vluggen21-Oct-09 3:18

Eddy Vluggen

21-Oct-09 3:18

ramz_g wrote:
All I'm using is a simple Sqlite database and I'm using simple queries where I have to use the windows logged-in user name.

A service is started before a user logs in to the system, and there might be more than a single user signed in. The simplest way would be to create a small application that writes the username to a file, and to drop it in the Startup-folder.

Alternatively, you might try WMI[^].

I are Troll Suspicious | :suss:

Re: Windows Identity of the currently logged in user

ramz_g21-Oct-09 19:15

21-Oct-09 19:15

Hi Eddy,

Thanks a lot for the replies..

Eddy Vluggen wrote:
The simplest way would be to create a small application that writes the username to a file, and to drop it in the Startup-folder.

I shall use this...

Thanks,
ramz_g

Safe Parallel loops

tvbarnard20-Oct-09 21:49

20-Oct-09 21:49

Good day

I've written code that is very computationally intensive, and therefore would like to use threads to parallel process the data (I've got a duo core pc)

The first solution I though of was to use "Parallel.For()" for the outer loop, but for some reason it corrupts my data.

This is the basic form of the code I want to parallelise:

List<int[,]> largeData; //a 5000x500 matrix
List<int[]> referenceList; //each int[] has about 10 elements
int answer;

//loops
foreach(int[] refArray in referenceList)
{
   foreach(int[,] largeMatrix in largeData)
   {
      answer = 0;

      foreach(int ref in refArray)
      {
         answer += largeMatrix[ref];         
      }
      
      //use "answer" for more processing here
   }
}

"Foreach" might not be the optimal choice for the loops, but I used it here to make the example simpler to understand.

I have tried replacing the first (outer) loop with Parallel.For(...), but then my "answer" value changes, implying that the threads corrupt the answer.

If you could help me with a "safe" approach of computing this in parallel I would greatly appreciate it, since figuring this out with almost no knowledge on threads is a daunting task.

tvb

stancrm20-Oct-09 22:27

stancrm

20-Oct-09 22:27

you must synchronized your thread using lock, mutex, ...
that is the only way to avoid corruption in your array.
you must split your large array in 2 blocks, and run
the first block in a thread, and the second block in a new thread.
if loop is finished, you can join them together.
Just replacing Foreach with Parallel.For is not the answer.

tvbarnard20-Oct-09 22:44

20-Oct-09 22:44

Okay thanks, that helped a lot Smile | :)

So when you say split the array in 2 blocks, do you mean run one half of second (inner) loop on a thread, and the other half of the loop on another thread?

tvb

stancrm20-Oct-09 22:55

stancrm

20-Oct-09 22:55

http://msdn.microsoft.com/en-us/library/system.threading.threadpool.aspx[^]

Learn first how to use a thread. Because it is not for beginner.

Just an easy sample :
You have an array 0,1,2,3,4,5,6,7,8,9
You want to sum it from 0 to 9.

For single thread, you must do it :
0+1+2+3+4+5+6+7+8+9 <- take probably 10ms (for example).

For multi threading, you must do it :
0+1+2+3+4 <- first thread -> resultA (take probably 5ms)
5+6+7+8+9 <- second thread -> resultB (take probably 5ms)
at the end, just sum resultA and resultB. (take all together 5ms, because resultA and resultB are parallel)

So, got it ?

tvbarnard20-Oct-09 23:06

Re: Safe Parallel loops [modified]

20-Oct-09 23:06

Yes, got it Smile | :)

tvb

Hristo-Bojilov20-Oct-09 22:38

Hristo-Bojilov

20-Oct-09 22:38

When syncronizing you would better avoid using mutexes and other kernel primitives.Just use monitors (locks) -they are about 20 times more faster and efficient than the mutexes and the other primitives. Smile | :)

And do not use large matrixes they could damage the app performance use vectors only.

[EDIT]
Replace large matrixes in your code with vectors.Use matrixes with small number of elements only. Cool | :cool:

Life is a stage and we are all actors!

modified on Wednesday, October 21, 2009 6:04 AM

tvbarnard20-Oct-09 22:45

20-Oct-09 22:45

Okay thanks,

If you don't mind, could you write the basic idea (in the context of my example code)?

I'm am an abolute noob to threads, so don't know where to start. I will read up on using monitors, but just need to know how the rest of the code would be structured.

tvb

Hristo-Bojilov20-Oct-09 23:55

Hristo-Bojilov

20-Oct-09 23:55

Here is a nice sample for parallel matrix multiplication.

Life is a stage and we are all actors!

tvbarnard20-Oct-09 22:47