Re: Iterating and Modifying a .NET Queue? - Visual Basic Discussion Boards

Re: Iterating and Modifying a .NET Queue?

AliAmjad13-Oct-07 6:22

13-Oct-07 6:22

Actually I'm working on a Distributed Web Crawler a Multithreaded application where each URL discovered will going to be added in a queue to implement the breadth-first search model. Many threads will access this queue and get the URLs from the top and then add the newly discovered URLs at the end of the queue and them remove the carwled URLs from the queue. Now what should i use in such a scenario. but when i implemented this logic i get this error "Collection was modified; enumeration operation may not execute".

AliAmjad (MCP)

Re: Iterating and Modifying a .NET Queue?

Dave Kreskowiak13-Oct-07 8:59

Dave Kreskowiak

13-Oct-07 8:59

Why are you enumerating them?? I don't see anything in this description that would justify it.

Well, now I see where your code came from. It's a modification of the sample code on MSDN.

You don't need a loop to dequeue items. The Dequeue method pops the top item off the queue and returns it an as Object. You have to cast the Object back to a String in order to use it.

Dim url As String = DirectCast(que.Dequeue(), String)

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Re: Iterating and Modifying a .NET Queue?

AliAmjad13-Oct-07 9:17

AliAmjad

13-Oct-07 9:17

OKKK i get it but as i am in a multithreaded application then lots of threads will access this queue then should i use SyncLock or what else to ensure thread safety.

AliAmjad (MCP)

Re: Iterating and Modifying a .NET Queue?

Dave Kreskowiak13-Oct-07 11:36

Dave Kreskowiak

13-Oct-07 11:36

Wrap the queue object in a class that implements adding and dequeuing. Use the SyncLock on an object to make it thread safe.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Re: Iterating and Modifying a .NET Queue?

AliAmjad13-Oct-07 23:08

AliAmjad

13-Oct-07 23:08

Cooool thanks buddy but I'm going to save MD5 hash algorithm of URLs in hexadecimal form in the Queue so which Queue(of T) i should use so that It'll consume as little memory as possible because I am gonna Enqueue it with lots of URLs. Again thanks for your valuable time Dave.

AliAmjad (MCP)

Re: Iterating and Modifying a .NET Queue?

Dave Kreskowiak14-Oct-07 2:37

Dave Kreskowiak

14-Oct-07 2:37

AliAmjad wrote:
but I'm going to save MD5 hash algorithm of URLs in hexadecimal form in the Queue so which Queue(of T) i should use so that It'll consume as little memory as possible because I am gonna Enqueue it with lots of URLs

That's nice. You better do some research on this first. MD5 is a one-way encryption hash. You can't reverse the hash and get the original URL back.

Forget hashing or compressing the URL. It's adding more complexity than you need, and unjustifiably so.

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Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Re: Iterating and Modifying a .NET Queue?

AliAmjad14-Oct-07 2:50

AliAmjad

14-Oct-07 2:50

Yes it is a one-way encryption hash and that's why I'll use these for the reference of original URLs saved in a file in this way I'll be able to store many URLs in memory because a web crawler needs to maintain a huge list of URLs in memory and also i'll calculate the MD5 for the page itself for preventing the duplicate entries in index because its size is very small and always equal. So what you suggest on this. Should i go with MD5 or just manipulate raw URLs in memory but this way it will consume lot of memory (RAM).

AliAmjad (MCP)

Re: Iterating and Modifying a .NET Queue?

Dave Kreskowiak14-Oct-07 7:50

Dave Kreskowiak

14-Oct-07 7:50

I don't see the need for MD5 anything in your app. On top of that, with the skill level you've shown in the original post, this shouldn't even be a concern to you right now. Just getting the basic functionality should be. Queue up URL's, dequeue one, download it and move on. THEN you can add complex indexing and hashing to your database.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Re: Iterating and Modifying a .NET Queue?

AliAmjad14-Oct-07 9:46

AliAmjad

14-Oct-07 9:46

Thank you very much man for helping me out I'll surely implement this valuable Logic and analyze the results then I'll tell you about it.

Dave Kreskowiak wrote:
The skill level you've shown in the original post

I consider myself as a beginner because I always try to grasp these important concepts and I've learned allot from you. What do you think about my Skill level? Am i capable enough to take this challenge of making a Distributed Web Crawler although I am up to some degree successfully able to achieve it. But still need a lot of guidance and help form people like you.

AliAmjad (MCP)

Working with bits in .Net

MatthysDT12-Oct-07 3:03

MatthysDT

12-Oct-07 3:03

I want to access a file bit by bit.

My problem is that .Net as not "bit" datatype other than boolean.
It has bitarray which could be fine, I'm not sure.

I already managed to read the file by looping through all its bytes by using the ReadAllBytes method but now I want to be able to alter the bits and write them back to a file. This file could be anything, a good example is a JPG image.

How should I go about doing this?

_______________________________________________________________________
http://www.notreadytogiveup.com/Doubts.aspx[^]
"you can't forget something you never knew..." M. Du Toit

Re: Working with bits in .Net

Dave Kreskowiak12-Oct-07 4:10

Dave Kreskowiak

12-Oct-07 4:10

That's where using masking, bitwise and logical operators, and math comes into play. If you're doing image processing, I highly suggest reading Christian Graus articles on "image processing for dummies[^]".

THe code is in C# because VB.NET doesn't support pointers.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Problem in Creating XML from Dataset in VB .NET [modified]

kkb_200112-Oct-07 2:13

kkb_2001

12-Oct-07 2:13

I have two XSD File. one is master and second is its child. i m creating the dataset from child XSD. now i m setting the data into dataset and then generating xml file from this dataset. it is working fine. But the problem is that the sequence(means order of the fields defined in Master Xsd File) defined in master file is not following in the xml file created thru DATASet.

can any body help me.
kishore

-- modified at 1:02 Saturday 13th October, 2007

Re: Problem in Creating XML from Dataset in VB .NET

Dave Kreskowiak12-Oct-07 4:05

Dave Kreskowiak

12-Oct-07 4:05

kkb_2001 wrote:
But the problem is that the sequence defined in master file is not following in the xml file created thru DATASet.

Sequence?? What "sequence"?? What are you talking about??

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Regarding Adam s post.......pls explain [modified]

Lins Dani12-Oct-07 1:28

Lins Dani

12-Oct-07 1:28

could anyone explain to me the codes dat are written for the dataset and datareader.............

-- modified at 23:39 Sunday 14th October, 2007

Regarding your post

MatthysDT12-Oct-07 3:07

MatthysDT

12-Oct-07 3:07

Could you please provide a permalink to "Adams post"?

_______________________________________________________________________
http://www.notreadytogiveup.com/Doubts.aspx[^]
"you can't forget something you never knew..." M. Du Toit

Setting PRIMARY KEY using Alter Table

Widgets12-Oct-07 0:35

Widgets

12-Oct-07 0:35

Guys im having a problem with this statement..

ALTER TABLE tblSample
ADD SampleField nvarchar (30) NOT NULL
CONSTRAINT SampleField PRIMARY KEY

im just trying to set my newly added column and at the same time setting it as a primary key.. but it wont work..

Is there any other way?
or can it set an existing non primary column to a primary one.. if it can then how.. thanks..

Re: Setting PRIMARY KEY using Alter Table [modified]

pmarfleet12-Oct-07 1:56

pmarfleet

12-Oct-07 1:56

This should work. What error are you getting?

BTW, you should really ask this question in the SQL forum. It has nothing to do with VB.

-- modified at 8:16 Friday 12th October, 2007

Paul Marfleet

Re: Setting PRIMARY KEY using Alter Table [modified]

kkb_200112-Oct-07 2:01

kkb_2001

12-Oct-07 2:01

it will not work because in sql u can not add column with Null having a primary key. it will work in access after removing nvarchar->char

-- modified at 4:34 Saturday 13th October, 2007

Re: Setting PRIMARY KEY using Alter Table

pmarfleet12-Oct-07 2:07

pmarfleet

12-Oct-07 2:07

I'm not sure why you replied to my message instead of the original poster. Anyway, it's pretty obvious from the query syntax that the database being used is SQL Server not Access.

Paul Marfleet

Message Removed

12-Oct-07 0:50

Marek Grzenkowicz

12-Oct-07 0:50

Message Removed

Re: Software Piracy

Guffa12-Oct-07 7:14

Guffa

12-Oct-07 7:14

Or just delete the question... that works too. Wink | ;)

---
single minded; short sighted; long gone;

Re: Software Piracy

Paul Conrad12-Oct-07 12:08

Paul Conrad

12-Oct-07 12:08

What was the deleted question?

"Any sort of work in VB6 is bound to provide several WTF moments." - Christian Graus

How to bind multiple tables in a datagrid..?

Balagurunathan S11-Oct-07 23:46

Balagurunathan S

11-Oct-07 23:46

Hi friends..

I have 3 tables in my dataset..I need to bind them to a single data grid.All the tables in the dataset have varying fields..How could i do this..Someone help in this regard as early as possible..

Regards,

Balaguru

Re: How to bind multiple tables in a datagrid..?

Vimalsoft(Pty) Ltd12-Oct-07 0:11

Vimalsoft(Pty) Ltd

12-Oct-07 0:11

hi

Use joins, and Add relations, if you are going to update the data later. you have to use DAl(Data Access Layer)

Hope it helps

Vuyiswa Maseko,

Sorrow is Better than Laughter, it may Sudden your Face, but It sharpens your Understanding

VB.NET/SQL7/2000/2005
http://vuyiswamb.007ihost.com
http://Ecadre.007ihost.com
vuyiswam@tshwane.gov.za

How to change to properties in vb.net

VB 8.011-Oct-07 22:41

VB 8.0

11-Oct-07 22:41

hii

In the datagridview ,i am showing the properties of a control like this using datatable

BackColor       BorderStyle   Enabled   Color          top    left <br />
 Color [White]	FixedSingle	True	Color [Black]	355	205	[Font: Name=Microsoft Sans Serif, Size=8.25, Units=3, GdiCharSet=0, GdiVerticalFont=False]	455	225	True	False	TextBox1

using this code

drTextBox.Item("Name") = ctr.Name<br />
            drTextBox.Item("BackColor") = ctr.BackColor.ToString<br />
            drTextBox.Item("BorderStyle") = ctr.BorderStyle

by setting previously at runtime . at this time it is storing in datatable .now i want to retrieve the same and show in propertygrid
and i am assigning to class .it contains properties get and set of textbox and i am assigning propertygrid.selectedobject = new ctextbox .

when i click on the control it has to show the properties by taking from datatable and assign to ctextbox(get, set) and show it in propertygrid .

I am getting the typecast error. how to typecast these things

i am taking it in a temporary variable and this variable i am assigning to ctextbox property get and set

tBackcolor = Color.FromName(drCurrentRow.Item("BackColor"))
MessageBox.Show(tBackcolor.ToString())

how to solve and show in the propertygrid

DVSriram

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