20 minute presentation on using Apple's Grand Central Dispatch for multithreading iOS applications. This talk was given at LiDG by David Fox on the 6th of April 2011.

1. An Introduction To Multithreaded
Applications Using Grand Central Dispatch
David Fox - www.davefoxy.com

2. Multithreading

3. So What IS GCD?

4. ^{
Prerequisite
Knowledge
}

5. Blocks
Portable Chunks Of Code

6. What’s A Block Look Like?
An in-line block
^{
// code goes here
}

7. What’s A Block Look Like?
A block stored in a reusable variable

8. What’s A Block Look Like?
A block using a custom block type definition

9. Back To The Point

10. The GCD Workflow
Create a queue to dispatch to
Dispatch blocks of code to that queue
And that’s basically it! (sort of)

11. In Action...
An Unresponsive App

12. Coding Demo Video
View online at www.davefoxy.com

13. Recap...
Create a queue with
Dispatch blocks of code using
Don’t mess with the UI on other threads

14. Taking It Further
Dispatch Groups

15. When Has GCD Finished A Block?
Using The Regular dispatch_async
Output

16. When Has GCD Finished A Block?
Using A Dispatch Group
Output

17. Encapsulating Queues
Using NSOperationQueue

18. The NSOperationQueue Workflow
Subclasses of NSOperation are created
Typically they override -(void) main
An NSOperationQueue is created and
NSOperations are added to it
The queue is set in action and the operations
are executed
Queues may be suspended so operations must
be aware of this

19. Operation Queues In Action
Simple Asynchronous Operations
Note: As OperationA and OperationB are running on the
same queue, operations won’t necessarily finish in the
order they’re added.

20. Operation Queues In Action
Listening For Individual Operation Completion

21. Operation Queues In Action
Waiting Until An Operation Queue Is Complete Before Continuing

22. Cancelling An Entire Queue
NSOperationQueues offer a
cancelAllOperations method
All the NSOperations will be notified of this
They can choose to perform certain actions
based upon their isCancelled property
Individual operations can be cancelled using
cancel

23. Loads More To Explore
Blocks instead of delegates
Dispatch Resources
Concurrent Operations
Semaphores
Delayed dispatches
Check The Apple Documentation

24. Thanks