Global NSOperationQueue - objective-c

Question

I'm trying to create a NSOperationQueue and add a NSOperation to it. Later I wan't to check if the queue is running and maybe abort it. All of that is supposed to be called from within different functions. What's the best approach to do this? I would be glad for a code example. Thanks!

Answer 1

I would create an operation queue that's managed by a singleton.
First, create your singleton class. It will provide access to the NSOperationQueue. Let's call the singleton MyGlobalQueueManager.
It will have an ivar called myGlobalQueue:
#property (nonatomic) NSOperationQueue* myGlobalQueue;
In the .m file of MyGlobalQueueManager, create a fairly standard init method that will set up the operation queue:
- (id)init
{
self = [super init];
if (self)
{
myGlobalOperationQueue = [[NSOperationQueue alloc] init];
}
return self;
}
Now, the method that provides itself as a singleton. Again, this is pretty standard stuff:
+ (MyGlobalQueueManager *)sharedInstance
{
static MyGlobalQueueManager *sharedInstance = nil;
static dispatch_once_t isDispatched;
dispatch_once(&isDispatched, ^
{
sharedInstance = [[MyGlobalQueueManager alloc] init];
});
return sharedInstance;
}
Let's access that queue from wherever you want to use it:
MyGlobalQueueManager* myGlobalQueueManager = [MyGlobalQueueManager sharedInstance];
NSOperationQueue *myGlobalQueue = myGlobalQueueManager.myGlobalOperationQueue;
You can then add operations to that queue as you fancy.
How to know if anythings queued?
NSUInteger count = [myGlobalQueue operationCount];
How to abort? Cancel everything as follows:
[myGlobalQueue cancelAllOperations];
Cancelling of course depends on the operations. If you're writing custom NSOperation classes, you'll need to handle that yourself.
I find NSOperation and NSOperationQueue to be fairly easy to use and quite straightforward.
A great document to read for all this is the Concurrency Programming Guide. Specifically, have a look at Operation Queues

Answer 2

An easier way to do it is to make a "globally visible" function. AKA, declare it in a public header:
extern NSOperationQueue * SharedQueue();
and define it within your compilation "unit" - but outside any #implementation.
NSOperationQueue *SharedOperationQueue()
{
static NSOperationQueue * _SharedQueue = nil;
return _SharedQueue ?: ^{ _SharedQueue = NSOperationQueue.new;
_SharedQueue.maxConcurrentOperationCount = NSOperationQueueDefaultMaxConcurrentOperationCount;
return _SharedQueue;
}();
}
As a little bonus.. #define it with an "alias".. and you can REALLy abuse it!
#define MY_SOQ SharedOperationQueue()
[MY_SOQ addOperationWithBlock:^{ /* GO CRAZY */ }];