The dispatch_get_global_queue
(DispatchQueue.global()
in Swift) gets you a background queue upon which you can dispatch background tasks that are run asynchronously (i.e. won't block your user interface). And if you end up submitting multiple blocks to the global queues, these jobs can operate concurrently. If you have multiple blocks of code that you want to submit to a background queue that you must have run sequentially in the background (not often needed), you could create your own serial background queue and dispatch to that, but if concurrent background operations are acceptable, then availing yourself of dispatch_get_global_queue
is convenient/efficient.
Be aware, though, that you're not allowed to perform user interface updates in the background queue, so the dispatch_async
to the dispatch_get_main_queue
(i.e. DispatchQueue.main.async { ... }
in Swift) lets that background queue dispatch the user interface updates back to the main queue, once the main queue is available.
This is a very common programming pattern: Submit something to run in the background and when it needs to perform user updates, dispatch the update back to the main queue.
For more information, refer to the Concurrency Programming Guide.
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