On May 10, 2012, at 3:42 PM, Dave wrote:
> We are using a third party library that performs tasks asynchronously. This
> is ok most of the time, but on some occasions I'd like to be able to wait
> (not on the main thread) until an operation completes,
This is usually an indication of a design problem.
> Is there a way of doing this and if so I'd be really grateful if someone
> could show me the code. I've tried using NSLock and NSConditionalLock etc.
> but can't get it to work!
NSConditionLock should work. You create it with a condition which you
arbitrarily decide means "unsignaled". The block locks it (without regard to
condition) and then immediately unlocks it in a different condition which you
decide means "signaled". The code that needs to wait just locks it when the
condition is signaled, unlocks it, and releases it.
Alternatively, you can use a dispatch_semaphore or dispatch_group for this.
Here's an implementation using dispatch_group (written in main, not tested):
-(void) doAtomicOperation
{
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
[self.mLibraryObject doOperation:myOperation
withCompletionBlock:^(void)(ResponseObject* theResponseObject)
{
// Do work
dispatch_group_leave(group);
}];
//**
//** Wait for Signal before continuing
//**
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
dispatch_release(group);
}
Regards,
Ken
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