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Basically a semaphore is an integer counter and a mutex it's a binary semaphore: it's a semaphore of max count 1.
They are restricted variables used in multi threaded programming environment to control the access to shared resources. By increasing or decreasing its value each thread knows if the resources are available or not.
Marc Soleda.
... she said you are the perfect stranger she said baby let's keep it like this... Tunnel of Love, Dire Straits.
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The classical example is to synchronize shared memory access between multiple threads.
A mutex can only be owned by a single thread at a time. Multiple semaphores can be created. In memory access, multiple readers are allowed but only one writer.
The two are used in conjunction. Study the following sequences until you understand how both readers and writers interact to synchronize thread safe memory access.
Before reading shared memory, a thread must execute the following sequence:
1) Acquire the mutex. If the mutex is not available, another thread is writing memory, and the reader must wait for the mutex.
2) After acquiring mutex, the reader knows it is "safe", i.e no other thread is writing to memory.
3) Acquire a semaphore. This is a signal that other threads may check to see if another thread is currently reading memory.
4) Release the mutex so the next reader thread may acquire the mutex just long enough to acquire a semaphore.
5) Read the shared memory.
6) After memory read is complete, release the semaphore, to signal that the thread is no longer reading the memory.
Before writing shared memory, a thread must execute the following sequence:
1) Acquire the mutex. If the mutex is not available, another thread is writing memory, and the second writer must wait for the mutex. Once a writer acquires the mutex, no other threads can access the memory for read or write, because both operations require the mutex, which is now locked by the writer.
2) Wait for all semaphores to be released. Threads that started reading the memory before the writer locked the mutex may not be finished yet. Once all semaphores have been released, the writer knows that no other threads are accessing the memory.
3) Write to the shared memory.
4) Release the mutex. Now other threads may acquire the mutex long enough to also acquire a semaphore, and start reading the memory again. Or another thread may acquire the mutex for a write operation.
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Mutex and sempaphores are generic terms for thread locking objects. These are the definitions used by the Microsoft handle objects.
Mutexes and Semaphores are similar. Licke marcdev said, you can set the max count lock count on a semaphore. A mutex behaves similarly to a single count semaphore, except for relocking the mutex by a thread. The thread that owns a mutex can lock it multiple times without stopping and it will allow another thread to own it after it unlocks it once for each time that it locked it.
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Thanks for all i got the difference.
Regards
Anil Kumar
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I am facing a strange problem att my job.. I'mnot a networking guy, but needs to the reason for following because tomorrow I have a meeting with other staf memebrs and boss for the feed back..
Lately our Web Server giving us a hard time becuase somehow it disables alll network connection and mapped drives and then we have to reboot it, after rebooting everything restores and starts working..
I know there might be lot of reasons for that but can some one tell me few of them please, I have to talk about it tomorrow.
Thanking all of you in advance.
Salim Akbar
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I posted this information in the lounge. Read the thread about shares between XP and 2K. I included some useful links in there. I can almost guarantee this is a permissions problem at the user level.
http://www.codeproject.com/lounge.asp?msg=1165084&Page=4&userid=440521&mode=all#xx1165084xx[^]
I know you can't become if you only say what you would have done and you'll miss a million miles of fun." - Len
Work hard, play hard. Don't forget who you are and don't forget where you're from. Do all these things well and you won't have to wonder where you are going.
Code-frog System Architects, Inc.
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Thanx for your reply..
Just one more thing for your kind info..
During that period the server does not run any scheduled jobs through SQL server..
Salim Akbar
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I don't think it has anything to do with SQL server. It's the permssions under which the drives are mapped and the credentials of the user accounts. That is probably the problem.
I know you can't become if you only say what you would have done and you'll miss a million miles of fun." - Len
Work hard, play hard. Don't forget who you are and don't forget where you're from. Do all these things well and you won't have to wonder where you are going.
Code-frog System Architects, Inc.
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code-frog wrote:
I can almost guarantee this is a permissions problem at the user level.
Can you give more reason, why it is relate to the permission problem at the user level? For my opinion, i don't think about permission problem. I think it might be relate to the network traffic which is over the ability of the server that could not handle it.
For network connection which is disable, i usually found this problem with my brother computer. I create an account for him as in a User level, but sometime when he start the computer, the network connection is disable but the cable still attach to his computer and the hub/switch is still running. Until i restart it again then it is start to work again. Until now, I still could not find the solution that why sometime network connection is disable when we start windows.
A thousand mile of journey, begin with the first step.
APO-CEDC
Save Children Norway-Cambodia Office
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Hi,
I am trying to develope a program for a client that allows them to view activity and the screen of several machines at once. I know that there are programs out there that allow you to do that, but the client is a teacher in a rural school district and can not afford them.
Thanks
Douglas Davis
Xenolith Technology Group
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it may be simple enough.
try this article:
http://www.codeproject.com/cs/media/directxcapture.asp
once you obtain the screen/audio data, sending them over the network is simple (or not?)
you can send some data packets (maybe screen frames compressed in jpg?).
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Thanks for the information. I think that this might be the answer to my problems.
Thanks Again.
Doug
Douglas Davis
Xenolith Technology Group
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XenoTech wrote:
I am trying to develope a program for a client that allows them to view activity and the screen of several machines at once.
In my opinion, i think you might need the student PC to access the teacher PC screen during the time that they take the lesson. How about sharing desktop with netmeeting?[^] Is this match what you need?
A thousand mile of journey, begin with the first step.
APO-CEDC
Save Children Norway-Cambodia Office
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Thanks for the information.
Thanks Again.
Doug
Douglas Davis
Xenolith Technology Group
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Hi,
I is a a very generic qurey (not associated with a particular software of hardware in specific)
I have and a hardware adapter with an FPGA in it. It could be connected to the PC via a USB port, with a driver for the same installed on the PC.
My query is, if I have two similar adapters which I connect to two ports. Will two drivers be required for it. Or will there be two instances of the same driver created
Could you please clarify.
Thanks,
Surbhi
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I would like to assign some text to some of the function key on the keyboard.
how is this done?
Also would it be safe to say have key F9 set to "myEmail@myISP.com" and F10 set to "myPassword".
Many thanks,
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If you are using VB and use the KeyCode event handler of the text, you will be able to perform an action based on the function key that you assigned.
A thousand mile of journey, begin with the first step.
APO-CEDC
Save Children Norway-Cambodia Office
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Are they any way within the operating system that will allow you to assign text to these keys such that when you press F9 when in a textbox the following text is entered into the box "myEmail@myISP.com" etc
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I don't know how to use it, but how about RegisterHotKey[^]?
"..Commit yourself to quality from day one..it's better to do nothing at all than to do something badly.."
-- Mark McCormick
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Hi
It is quite simple. first you sould use the RegisterHotKey API for example for F9 key. Then in your program's main window's winproc function, write code for WM_HOTKEY to get when the desired hotkeys are pressed. Then use the SetWindowsText API function to set the desired text on whatever window you like or more easily, call kybd_event API function to simulate keyboard input.
If you have question about any of these steps, let me know and I would describe.
Hope it was helpful
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Thanks for the post.
Just one futher question, if I wrote a program that assigned F9 and F10 as hot keys (with some text), then I ran this program when Windows starts up would the text assigned to F9 be placed into a text field when pressed F9 is pressed in another standard WIndows application.
i.e.
if F9 = "myEmail@myISP.com"
F10 = "myPassword"
when prompted for my e-mail and password could I just press F9 then Tab to the next field and press F10?
Many thanks,
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Ofcourse!
The hotkey has in fact been produced for the same reason, while you can simply get the Key_Pressed event when the focus is on your own program!!
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What I was after was when the HotKey is pressed when another Windows program requires text input, then the pre-defined text would be entered into the text area; e.g. userName and password.
The other program does not know about the HotKeys.
I can see how to register and unregister HotKeys and use them in my programs, but its other Windows programs.
Maybe I am thinking of a Macro key press sequence.
The question was can some keyboard keys be assigne some text strings that will be entered into text fields which are active in another program when these keys are pressed?
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Hi, I am interested in how different companies manage to create a blue screen which halts the operation of the computer until it does what it wants to. For example Symantec, the people who create Norton antivirus, create a blue screen when you rename your hard disk; and there is another company who actually stop the booting of windows to bring up a screen where it does registry defraging.
So how would you create something like this?
Thanks,
IanG
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IanG (Surreal Studio) wrote:
For example Symantec, the people who create Norton antivirus, create a blue screen when you rename your hard disk
In Win 9x, the real-time scanner navap.vxd uses a kernel-mode call to switch to text mode and show the prompt.
--Mike--
Visual C++ MVP 
LINKS~! Ericahist | 1ClickPicGrabber | NEW~! CP SearchBar v3.0 | C++ Forum FAQ
You cannot truly appreciate Dilbert unless you've read it in the original Klingon.
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