What's the difference in sync and async programming on iOS? When would you use each?

Question

Anonymous · Accepted Answer

sync is when the code is executed in the order that it's written in, async means
that the code inside the async block is run on a separate thread, and the
programmer can't rely on the code running in the sequence it was written in.
usually, for async, there's a callback method that the thread will execute after
the async functionality returns. sync is used generally for code that needs to
run in order, and async is used for actions that can take some indeterminant
amount of time to come back, such as IO, networking, or graphics related
functionality. a special thread on ios is main, which is the only thread that
can execute UI related code. It's important to make sure you only update the UI
from the main thread, otherwise your app will crash. So, for example if your
code uses a different thread to get data from your backend async (because it
will take time for the request to return), you'll have to call the main thread
to update with the data after your request comes back.

Anonymous · Answer

Synchronous calls blocks the thread and other instuctions can not continue while
the sync call is getting done. On iOS having a synchronous call on the main
thread will mean it block the UI.

On the other hand Async is not blocking and returns immidiately. Letting the
other instructions continue while the async task is being performed.

What's the difference in sync and async programming on iOS? When would you use each?

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