Stopping a thread before it ends

[hehe0613]

Hello All

My application loads images from internet in a detached thread, as follow :

[self performSelectorInBackground: @selector(displayProductsImages withObject: theProduct];

- (void) displayProductsImages: (Product *) theProduct
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// code that download images using dataWithContentsOfURL function
.....
[pool release];
}

It works fine, but in some circumstances I need to stop the detached thread before it ends naturally. Unfortunately I cannot find any simple function that would allow me to stop this thread ?

I tried using cancelPreviousPerformRequestsWithTarget but no success !

Any idea would be greatly appreciated !

[RLScott]

If you force an end to a thread, then there would be no opportunity for that thread to clean up its resource allocations. So instead of trying to force an end to the thread, look for ways to change the thread so that it periodically checks for a notification from the main UI thread that it should stop. Then the worker thread can gracefully stop what it is doing and exit.

[hehe0613]

Originally Posted by RLScott

If you force an end to a thread, then there would be no opportunity for that thread to clean up its resource allocations.

Right, as mentioned in the documentation

Originally Posted by RLScott

So instead of trying to force an end to the thread, look for ways to change the thread so that it periodically checks for a notification from the main UI thread that it should stop. Then the worker thread can gracefully stop what it is doing and exit.

Hmm yes, but I will have to count the number of actives threads I think.

I currently have a view controller which launches this loading image background thread.
In another view controller (parent of the above view controller), users can click a button which will have for effect to load new images in the child view controller.
If the user clicks fast on the button, for instance 3 times, what I observe is :
- the image which corresponds to the first time the user clicked is displayed
- the second image is then displayed once loaded
- the third image is then displayed once loaded

In the above case, I need to stop loading the images of the 2 first clicks to only display the third. Should I count the number of active threads and display image only if the last thread ?

something like :

- (void) displayProductsImages: (Product *) theProduct
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

nbThreads = countTheNbOfActiveThreadsInThisViewController();

if(nbThreads == 1)
{
// code that download images using dataWithContentsOfURL function
.....
// code that displays the loaded image
....
}

[pool release];
}

If the above seems correct, I need to be able to count the numbers of active threads, is there a way to do that ?

Thanks again for your time, really appreciate ...
J

[Jeremy1026]

I'd do an if statement.

 - (void) thread {
NSAutoRelasePool *pool...
if (!threadIsRunning) {
threadIsRunning = YES;
// Download Image
// Download Finishes
threadIs Running = NO;
}
[pool release];
}

That assumes you have properly declared threadIsRunning as a BOOL in your header file.

[hehe0613]

Originally Posted by Jeremy1026

I'd do an if statement.

 - (void) thread {
NSAutoRelasePool *pool...
if (!threadIsRunning) {
threadIsRunning = YES;
// Download Image
// Download Finishes
threadIs Running = NO;
}
[pool release];
}

That assumes you have properly declared threadIsRunning as a BOOL in your header file.

Thanks for your answer, but what you mentioned will have for effect to load ONLY the first image, I need to display only the latest, not the first !
Am I wrong ?

[Jeremy1026]

it would limit it to one load at a time, so if the user presses the button 10 times quickly, only the 1st and 10th image would load.

[hehe0613]

Originally Posted by Jeremy1026

it would limit it to one laod at a time, so if the user presses the button 10 times, only the 1st and 10th image would load.

the 10th image would be displayed only if the first has been completely downloaded.

If the user presses the button only 2 times, very fast, the second image will not display ... since the first is still downloading.