Hi,
I am migrating my code to use GCD blocks instead of NSOperations.
NSOperation has a -cancel method to thread-safely notify the
NSOperation thread that it needs to be canceled.
How do you do this for an async GCD block?
I.e. suppose I have the following code:
@implementation MyClass
- (void)myMethod
{
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
^{
do_some_lengthy_cancelable_operation();
});
}
@end
I need to be able to cancel do_some_lengthy_cancelable_operation() at
some point.
The first solution that comes to my mind is the following.
@interface MyClass <MyCancellableOperation>
{
bool m_isCancelled
}
- (bool)isCancelled;
@end
@implementation MyClass
- (void)myMethod
{
dispatch_async(
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0),
^{
do_some_lengthy_cancelable_operation(self);
});
}
@end
void do_some_lengthy_cancelable_operation (id<MyCancellableOperation> operation)
{
for (int i = 0; i <BIG_NUMBER; ++i)
{
if ([operation isCancelled])
{
break;
}
}
}
But this seems a bit clunky (compared to the elegance of GCD code),
and also I'm not sure if it will be thread-safe to set m_isCancelled
from the main thread, while the async block may be racing to query it
(though it should be fine, setting a boolean variable should be
atomic).
Is there a better solution?
Thanks,
Oleg.
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