CODEWITHSUNDEEP
iphoneiosnsoperation
James Huddleston
James Huddleston

Reputation: 8448

Writing NSOperation-friendly methods

I have an object (Processor) containing several methods that perform lengthy calculations. I'd like to use those methods both on the main thread and in NSOperation subclasses.

Inside my NSOperation subclass code I repeatedly call isCancelled, so cancellation is fairly responsive. However, when the operation calls one of those lengthy Processor methods, it isn't able to respond to cancellation until that method returns.

Is there a good way to write methods so they can be used both with and without operations? I'm considering adding an operation argument to my CPU-intensive Processor methods and writing them like this:

- (void)calculateWithOperation:(NSOperation *)operation {
    do {
        if (operation != nil && [operation isCancelled]) {
            return;
        }
        // Do some more calculation...
    } while (! finished);
}

// For convenient main thread execution.
- (void)calculate {
    [self calculateWithOperation:nil];
}

Has anyone else run into this issue before? Is there a better way?

Upvotes: 2

Views: 238

Answers (1)

Costique
Costique

Reputation: 23722

The only way for an NSOperation to respond to canceling is to check if it's isCancelled as frequently as feasible. After all, it's just a thread which needs to exit when a flag is set. Basically, the isCancelled infrastructure is needed to gracefully free the operation's resources. So I'd say you just have to pepper the expensive method with checks.

Upvotes: 2

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