An Introduction To Multithreaded Applications Using Grand Central DispatchDavid Fox - www.davefoxy.com

Multithreading

So What IS GCD?

^{ Prerequisite Knowledge}

BlocksPortable Chunks Of Code

What’s A Block Look Like?

^{// code goes here

}

An in-line block

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

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

Back To The Point

The GCD Workflow

Create a queue to dispatch to

Dispatch blocks of code to that queue

And that’s basically it! (sort of)

In Action...An Unresponsive App

Coding Demo VideoView online at www.davefoxy.com

Recap...

Create a queue with

Dispatch blocks of code using

Don’t mess with the UI on other threads

Taking It FurtherDispatch Groups

When Has GCD Finished A Block?Using The Regular dispatch_async

Output

When Has GCD Finished A Block?Using A Dispatch Group

Output

Encapsulating QueuesUsing NSOperationQueue

The NSOperationQueue Workflow

Subclasses of NSOperation are createdTypically 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

Operation Queues In ActionSimple Asynchronous Operations

Note: As OperationA and OperationB are running on the same queue, operations won’t necessarily finish in the order they’re added.

Operation Queues In ActionListening For Individual Operation Completion

Operation Queues In ActionWaiting Until An Operation Queue Is Complete Before Continuing

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

Loads More To Explore

Blocks instead of delegatesDispatch Resources

Delayed dispatches

Concurrent Operations

Semaphores

Check The Apple Documentation

Thanks