To stop some activity

rajeevktripathi

Hi All working on a dialog based application, where the entire registry is scaneed for errors, For Registry using SDK functions ( RegOpenKey(), RegEnumKey( ) etc.) Now what my problem is: while scanning is going on ( there is a button "STOP" on the dialog) if user press or click on the STOP button then the the scanning of Registry should be stopped and a messagebox should appear for resume or exit operation. I think problem would be clear... So please suggest me the scenario to implement this and better if provide some code snippet for the same. Thanks

Cedric Moonen

Start the scanning of the resgistry in a separate thread that runs an "infinite loop". This loop can be finished either when the scan is complete or when a variable is set to false. Something like that (pseudo-code):

while (bContinue)
{
// Process next key
if (LastKey == true)
bContinue = false;
}

This variable can be set through the main thread but you have to make it thread safe (for example use a critical section). If you are new to thread, I suggest you read some documentation about that because it can be difficult for a beginner.

Cédric Moonen Software developer
Charting control

ovidiucucu

First, I would like to recommend instead a message box, two buttons "Pause" and "Stop" in your main dialog. Perform the registry scanning in a worker thread. When press "Pause", call SuspendThread dunction in order to suspend registry scanning and change the button caption from "Pause" to "Resume". When the user press "Resume", call ResumeThread to start scanning again. When the user press "Stop" you can call TerminateThread. Ovidiu Microsoft MVP - Visual C++ @to Cédric: Why "infinite loop"? -- modified at 10:09 Friday 23rd June, 2006

Cedric Moonen

ovidiucucu wrote:

Why "infinite loop"?

I prefer using a loop that you can fully control instead of killing the thread with terminate thread. The reason is if you want to make some 'clean-up' after the loop (ok, maybe infinite loop was not the right word but I meant a loop that finishes when one of the condition is met).

Cédric Moonen Software developer
Charting control

David Crow

Using SuspendThread() and TerminateThread() is very risky, and not nearly as simple as you've described here. Before a thread suspends itself, it needs to ensure that by being suspended, the calling thread is not affected. If a synchronization object is being held by the thread, it would need to be released. Suspending a thread from another, without taking all of the precautions, is not a good idea because the thread being suspended might be in the middle of something important (e.g., memory allocation). This could result in your application entering a "hung" state. If a thread calls TerminateThread() on itself, there is no chance for cleanup. The thread goes away right then and there.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

ovidiucucu

You are double-right. First when say "maybe infinite loop was not the right" because registry is a finite stuff and sooner or later its scanning have to finish, regardless the user pushes "Stop" or not. ;-) Second, indeed for the sake of good recommendations we have to avoid TerminateThread, which in our case can let a registry key open for reading which can lead in unpredictable, catastrophic effects. :) Ovidiu Microsoft MVP -- modified at 10:25 Friday 23rd June, 2006

ovidiucucu

So, instead of SuspendThread/ResumeThread the right solution is... Ovidiu Microsoft MVP

David Crow

I didn't indicate they couldn't be used. You have to be very careful when using them, however.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Jun Du

Avoid TerminateThread(). A thread synchronization should be implemented to allow the thread function to complete/end gracefully. Best, Jun

rajeevktripathi

Thanks u all Infact I am new to threading programming. Though have some theortical basics of the concept. So u r requested to tell me the link to begin with so that things could be more clear. Thanks