C# Discussion Boards - CodeProject

Best code for this multithreading issue?

5-Jan-04 7:15

Or simply Process.Start (a static method - an instance of Process isn't necessary).

Also, this question has been asked MANY times in the past and even once today just shortly before you asked. Please search the comments before posting.

-----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-----

Re: starting other apps?

Guillermo Rivero5-Jan-04 7:22

Guillermo Rivero

5-Jan-04 7:22

How many times have you answered this question ??? Laugh | :laugh:

Free your mind...

profoundwhispers5-Jan-04 6:32

profoundwhispers

5-Jan-04 6:32

Currently, I'm fetching page IDs from an XML file.

I want to write code that does the following:

1- Add these IDs to an array? arraylist? some kind of list?
2- Start 5 threads that will access this list simultaneously and download a page from the internet (for example http://www.page.com?pageid=ID) provided that each page should be downloaded only once.
3- These pages are saved on disk.

What happens in case of a powercut? How can I know which page did I stop at?

Thank you very much.

Sammy

"A good friend, is like a good book: the inside is better than the cover..."

Re: Best code for this multithreading issue?

HAHAHA_NEXT5-Jan-04 7:22

HAHAHA_NEXT

5-Jan-04 7:22

1- Create a global variable to give the pages to download and create 5 other variables to specify which page a tread is currently downloading.
2- Each time a tread finishes to download a page, it increases the global variable by one and sets its own variable to the page it curently downloads.
5- Save on a file, all the 5 variables and the gloabal one. In the case of power goes down, you will simply resume the 5 pages and will continue with the gloabl variable.

Ex:
a,b,c,d,e are the current location of download of all the treads.
g is the gloable variable,
1,2,3 ... 20 are pages to download.
Stuff in bold is already downloaded.
Thus you get:
1 2 3a 4 5 6b 5 7c 8 9 10 11d 12e 13g 14 15

In the case If power goes down, will will simply have to download pages 3,6,7,11,12 and then to continue with pages 13+.

Re: Best code for this multithreading issue?

Heath Stewart5-Jan-04 7:28

custom save/open file dialog

5-Jan-04 7:28

profoundwhispers wrote:
What happens in case of a powercut?

Confused | :confused:

What do you mean a "powercut"? If you mean loss of power, the only way you can know which threads didn't finish is to use a file to persist each thread's URL that they're working on and whether or not they've finished. This is common in many caching situations.

As far as using threads, using an array list isn't really necessary because you'll have to pass an index to each thread for them to determine which one to work on. Instead, read each ID from the XML file like you're doing and use asynchronous calls to download the file, like HttpWebRequest.BeginGetResponse. You'll pass an AsyncCallback that can write to that cache file I mentioned. If you track how many IDs you read and then keep a counter for how many times the callback was executed (be sure to use locking to increment the counter to make sure, for instance using the lock keyword) you can know which ID was last (by checking the IAsyncResult.AsyncState, which you would pass into HttpWebRequest.BeginGetResponse - this is used to pass custom data from the async call to the callback for cases such as this).

You could also devise a similar situation using the ThreadPool.QueueUserWorkItem, which also uses a delegate to start in a new thread and accepts a state object (which can be a single object of any type, including an array, list, or collection of other objects). The simple Thread class doesn't now allow such state variables and there is additional benefits to using a ThreadPool over simple threads. (See the SDK documentation for details.)

I would recommend asynchronous calls, though. The functionality is provided so you might as well use it. Also keep in mind that if you devise your own system using delegates, that the C# compilers (and probably others) automatically add asynchronous versions of the Delegate.Invoke function so you can use delegates asynchronously, too.

misterbear5-Jan-04 6:31

misterbear

5-Jan-04 6:31

Hi.

I need to have custom save/open file dialogs but
since the .NET ones are sealed it can't be inherited, neither can the FileDialog class from which they inherit. Does anyone know of a good approach to creating a custom dialog for this purpose? What I need is something as simple as an
additional textfield rightmost in the dialog.

I would really really(!!) want to use the functionality in the available controls. I have come up with two approaches, of which the second I really don't know how to do.. =)

either (1) create a new control which aggregates a SaveFileDialog control for some functionality (like opening the stream to file, etc.)
or (2) make it 2 separate windows that stay next to each other, and remove the window decoration.

any more suggestions? Has anyone done this? Please let me know if you think you can help.

Re: custom save/open file dialog

Heath Stewart5-Jan-04 7:13

Re: custom save/open file dialog

5-Jan-04 7:13

I've been discussing this with some other developers - including some Microsoft developers in the forums - and there isn't a way without going to a LOT of work. Basically, you have to encapsulate the functionality of the GetOpenFileName and GetSaveFileName functions, as well as the OPENFILENAME struct. This is what the OpenFileDialog and the SafeFileDialog (which inherit most of the functionality from the FileDialog class) do.

The biggest problem is dealing with the dialog template you'd assign to the lpTmeplateName member of the OPENFILENAME structure. In Win32 this isn't too hard because you can use resources (stored in the .rsrc section of a PE (portable executable)). To have this managed is definitely NOT easy! The engineers I even talked to do mentioned something along the lines of "not having time" to do this for 1.0 (which, since it's still not in 1.1 and doesn't appear to be in 2.0 means, "it's too hard").

If you want this managed, there are ways of making a DLGTEMPLATE out of a dialog resource (namely, your Form or Control that will physically extend the open and safe file dialogs), but you have to worry about converting units from pixels to dlg units and a lot more. There was an example I found on the 'net but I don't remember where. Just google for it if you dare try this. You'll need to P/Invoke all that code used in the exmample, as well as things like the GetDeviceCaps to get the proper unit measurements.

My recommendation is to write a native DLL that does this instead. You can then encapsulate your own custom open or save file dialogs in a Component like Microsoft does. Just make sure you distribute this native DLL with your application, putting it in a location that can be resolved (like the current working directory or any directory in the PATH environment variable). I don't have a sample because this alternative doesn't really work for my company because we use an Internet-deployed (ala touchless deployment) app and try to avoid native resources at all costs. I found a way around using a different approach.

misterbear5-Jan-04 8:43

misterbear

5-Jan-04 8:43

Ok thanks, great answer =)
I don't really mind doing it the native way it's
not gonna be a problem for me.. But I'm not really big on windows .dll programming. Do you have any hints / directions as how to do this 'the native way'? Any good links for tutorials or so?

Also I once found some kind of solution to this problem my combining multiple windows and make them look like just one. Since I only need to add a component rightmost in the dialog, this would be a possible solution for me... Any ideas as to how this can be done?

Re: custom save/open file dialog

Heath Stewart5-Jan-04 9:52

5-Jan-04 9:52

For an example of encapsulating a custom method and struct, use a decompiler like .NET Reflector[^] and see how the FileDialog and its derivative classes work. That's the best thing I can tell you.

You could just have a simple native function in a native DLL that you can call, passing parameters as necessary or use a struct like the OPENFILENAME struct, though you could cut down on the members needed for your implementation.

As for the other idea, neither the GetOpenFileName, GetSaveFileName, or the OPENFILENAME struct accept positional values. Since the FileDialogs merely use these functions and structs, it won't know either (nor does it have positional properties of its own). You'll have to get a HWND of the dialog instead, most likely using FindWindow, and you could try encapsulating this by extending the NativeWindow class (a managed wrapper for existing windows) and use AssignHandle, passing the HWND that you got from FindWindow. You could then figure out the position and track it with another window.

There might be an easier way to do this alternative, but this is just off the top of my head and without any research. You could search to see if an easier / better way exists.

Easy Form Question

Guinness4Strength5-Jan-04 6:19

Guinness4Strength

5-Jan-04 6:19

Anyone ?

How do I prevent the user from resizing my Form ?
i.e. Dragging the edge of the dialog box to make it wider/taller.

AND/OR

How do I resize a Tab Control ?

Re: Easy Form Question

Heath Stewart5-Jan-04 7:04

5-Jan-04 7:04

Guinness4Strength wrote:
How do I prevent the user from resizing my Form ?

Set your Form.FormBorderStyle to FormBorderStyle.FixedDialog. Also, this question was just asked and answered this morning. Please search comments before posting.

Guinness4Strength wrote:
How do I resize a Tab Control ?

Same as any other control - just set its TabControl.Size (as a Size struct - setting the individual properties will not work since it's a value type), or set the TabControl.Width and TabControl.Height properties. All these properties inherit from Control.

Re: Easy Form Question

Niels Penneman5-Jan-04 10:11

Niels Penneman

5-Jan-04 10:11

Did you mean resizing a tab control in the designer? You must make sure you don't select a tab page, to resize the control you must select the whole tab control (do not click on a tab or page).

To restrict the size of your form you could also use MinimumSize & MaximumSize

greetz
Niels Penneman

Run a External EXE File

hxxbin5-Jan-04 6:16

5-Jan-04 6:16

Hi
I'm trying to do a Windows Service for a EXE file based at Console. But I don't know how run this file at the background, anyone knows??

Thanks

Heath Stewart5-Jan-04 7:00

5-Jan-04 7:00

This question doesn't make sense. Are you trying to start a normal application? See Process.Start. Are you trying to start a Windows Service? See the ServiceController class. You can find more information about these in the .NET Framework SDK.

hxxbin5-Jan-04 7:07

5-Jan-04 7:07

Let me explain about.

I already have a console application, that controls a RH DB, and need to be started from a logged user into a w2k server. For this reason, I was thinkin' create a Windows Service, that run this application without a logged user, like any service as IIS.

I will check Process.Start but it could be helpful any extra information that you can give me about.

Thanks.

Heath Stewart5-Jan-04 7:37

5-Jan-04 7:37

Windows Services do run under user credentials, be they SYSTEM, SERVICE, IUSR_COMPUTERNAME (default for IIS), or a specified user. It just doesn't have to be executed by a logged-in user.

You could use a Windows Service, but you should then use the ServiceController class. If you want to allow interaction by controller applications by the user (like a Control Panel applet or some application), you'll need to allow for desktop interaction. If you use the ServiceInstaller and ServiceProcessInstaller classes to install the service, you'll have to use the Microsoft.Win32.Registry class and related classes to set this property in the registry. If you don't need to use an installer (for example, for mass deployment) then you could just use the Services snap-in to do it manually.

hxxbin5-Jan-04 8:42

5-Jan-04 8:42

Thanks for the help

Now, the Services run on my machine, I'm trying to make a Installer with the Deploy Template, but isn't work, the application installutil is installed with the .NET Distribution???, I don't wanna install de .NET Framework SDK into the server.

Heath Stewart5-Jan-04 9:37

5-Jan-04 9:37

Yes it is, but you have to add the Framework path to your PATH environment variable or execute installutil.exe using the fully-qualified path. The path for .NET 1.0 is %WINDIR%\Microsoft.NET\Framework\v1.0.3705 and for .NET 1.1 %WINDIR%\Microsoft.NET\Framework\v1.1.4322.

Make sure your Installer class is attributed with the RunInstallerAttribute. For an example, see the ServiceInstaller class documentation (for the class itself).

hxxbin5-Jan-04 11:33

Re: Cryptography Question

5-Jan-04 11:33

It's Works Finally, Thanks you are so helpful. The WinService now is running, and I installed into the server, I didn't need add manually.

I'm happy now Big Grin | :-D

Cryptography Question

Mazdak5-Jan-04 4:09

Mazdak

5-Jan-04 4:09

Today I start some playing with Cryptograhy classes and I encounterd a problem,I hope someone can display it for me.

I create a file and encrypt it to another file to see the value. It works Ok,then I do it again with the same key but changed the value of IV for the key,the output changed ! Now I decrypt these two output with the same key but different IV and they decrypt to original values correctly. The question is:

I changed vectors(IV) for the key and I get different ENCRYPTED value but changing IV return the same DECRYPTED value.

Thanks

Mazy

No sig. available now.

Heath Stewart5-Jan-04 5:18

Re: Cryptography Question

5-Jan-04 5:18

Different initialization vectors (IV) should produce different content with symmetric encryption. It's the key that is important and must remain the same. The encrypted content is often different - especially with asymmetric algorithms - because a number of factors are used to encrypt the content. For example, often the IV is randomly generated, and random generators are often seeded with an aspect (like ticks) of the current time.

If you're interested in cryptography, you should read Applied Cryptography, 2^nd Edition[^] by Bruce Schneier, one of the leading cryptoanalysts (and a good writer to boot) today.

Mazdak5-Jan-04 7:46

Mazdak

5-Jan-04 7:46

Thanks Heath,I don't understand whats the role of IV from the docs I have,can you give me your view about it?

Thanks for the book too,I'll buy it,now I'm reading .NET Framework Security[^]. Its a little hard for me but little by little I'm going through it. Smile | :)

Mazy

No sig. available now.

Re: Cryptography Question

Heath Stewart5-Jan-04 9:32