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G'day everyone. Welcome back.

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In this video, we'll have a quick look at another way to run code on a background thread.

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Kotlin Coroutines provide similar functionality to threads,
but they're much more efficient.

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The reason is, that creating a new thread takes time.
It's quite an expensive operation to perform.

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In our code, we only create one thread at a time.

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Just to be clear, we haven't introduced any significant performance problems,

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and using a thread is fine for our database accesses.

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Coroutines can be extremely useful if you're creating lots of threads.

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If you were doing it in a loop, for example, then the overhead of creating each thread could become significant.

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Coroutines use a shared pool of threads that have already been created.

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That means they remove the overhead of creating new threads,

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and are great if you're starting background tasks repeatedly.

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To switch to using a Coroutine instead of a thread,
we just have to replace thread with launch.

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Until recently, Coroutines were an experimental feature of Kotlin.

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They've now made it into the latest version,

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but you will have to make sure that you're using at least
version 1.3.20 of Kotlin.

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We can check that in the project build.gradle file.

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Here we can see that we are using Kotlin version 1.3.21, which is greater than 1.3.20.

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Obviously, you can't just change that,
if you haven't updated your Kotlin plugin

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when Android studio prompts you to,

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so make sure you have accepted all the updates,
before changing the version in this file.

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Next we have to add the Gradle dependency to our
build.gradle module file.

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Sync it now, and then let's have a look
at the changes we need to make in TaskTimerViewModel.

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The change is simple. We change thread to globalScope.launch in both places that we've used it;

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here

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and down here.

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Android Studio should have added two imports for us;

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kotlinx.coroutines.GlobalScope and kotlinx.coroutines.launch

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If it has left the import for Kotlin.concurrent.thread in the imports, we can delete it.

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Okay, let's see if it works.

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Run the app again, then select the process and task ID
and use control F to highlight all occurrences.

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The query is being executed on a different
thread, and when I delete task two,

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that also happens on a background thread.

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What you may find this time, is that the thread ID for the delete,
is the same as the ID for the subsequent re-query,

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or, it may be the same as an earlier thread,
when the database was first queried.

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With coroutines, threads are reused from a pool of threads,

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which reduces the overhead of creating them each time.

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You may not get the same thread ID every
time of course, that's not guaranteed.

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I'm just demonstrating that the threads can be reused,
when you use coroutines.

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Okay, now that we've got a couple of ways
to access the database on a background thread,

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we'll clean up our add/edit fragment.

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It shouldn't be saving the data.

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That function should be moved into the ViewModel.

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The database access to save the data should be performed
on a background thread as well.

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We'll make both those changes in the next video.

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Look forward to seeing you there.