On Nov 11, 2010, at 8:13 AM, Shane wrote:
> I've got an NSOperation thread running, but I'd like to be able to
> send a message to it so that the thread can be shut it down, or
> possibly other commands.
>
> What is considered a good way to send a message to an NSOperation
> thread from the apps main thread?
Usually, NSOperation objects execute on threads managed by the corresponding
NSOperationQueue where you added them, e.g.:
MyOperation* op = [[MyOperation alloc] initWithMyParams:params];
[self.myOperationQueue addOperation op];
So, whatever operation queue you use, the *operation queue* is responsible for
managing the threads your operation will execute on. The operation queue hides
the complexity to create and destroy the threads - which is a good thing. Which
threads the operation queue creates and when is a private thing to the
operation queue. So, you should not bother with this.
Note, that there is a global queue [NSOperationQueue mainQueue] which executes
its operations on the main thread.
In order to cancel an *operation* (not a thread) you can send the operation
object the -cancel message from any other execution context. All what is
required is to design the method -main of your operation such that it
periodically checks whether it has been cancelled, e.g.:
- (void) main {
if ([self isCancelled])
return;
BOOL done = NO;
while (!done) {
// do a peace of work
// ...
if ([self isCancelled]) {
// optionally send the "delegate" a notification about the
cancellation.
return;
}
}
// send the "delegate" a message about the result of the operation
}
Note: "delegate" is defined in your custom Operation.
When you send (custom) messages to an operation, you should care about proper
synchronization if necessary.
see also:
NSOperationQueue: -cancelAllOperations
NSOperation: -cancel
NSOperation: "Responding to the Cancel Command"
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/NSOperation_class/Reference/Reference.html
http://developer.apple.com/cocoa/managingconcurrency.html
Have fun!
Andreas
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