WEBVTT

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>> Hey, friends. Were back
with my good friend Dean

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talking in advanced
Async Await, so tune in.

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[MUSIC]

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>> Welcome back everyone
to the Xamarin Show.

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I'm your host James Montemagno.

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Today, back for the second
time my good friend

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Dean on talking about Async
Await. How's it going, Dean?

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>> Good. How are you?

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>> I'm doing absolutely fantastic.

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Now, in the first episode,

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you showed off basic use
cases of Async Await,

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what's wrong, what's good.

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What you got in store for us today?

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>> So this time around,

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we're going for advanced scenarios.

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A bunch of edge cases.

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Advanced scenarios using
different mechanisms

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within the TPL and going deep.

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>> Very awesome. Cool. I love it.

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Well, let's waste no time at all
and let's get into the codes.

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>> Let's get right to it. All right.

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For the last one this is the most,

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I don't want to say complicated,

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but a very big edge case.

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>> All right.

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>> So what this is long running
tasks. So you're familiar?

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>> I am.

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>> So long running tasks in

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the TPL are tasks that
can run for a long time.

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Sometimes, you just
want something to run.

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Maybe it's pulling, maybe it's
checking your accelerometer values,

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something like that,
running in the background.

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You don't really want to stop it.

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So in a bad case,

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in my bad example here,

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I'm going to start

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a 100 tasks that are
printing dots every second.

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>> That makes sense.

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>> They're just going to be running.

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Fire and forget, forget about
them, and they'll just run.

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>> Visual Studio is even yelling you.

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>> Exactly. The Visual
Studio is smarter than me.

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Then, on top of that,

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I'm going to run a 100 tasks
that actually complete.

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>> Okay.

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>> So we'll see what
happens to these.

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So these tasks are the
tasks that in your app,

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you actually want to run,

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maybe you're downloading HTML,

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downloading images,
doing things like that.

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All right. So here's a bad example.

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We're running a 100 tasks
which print dots every second.

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So each one of these
tasks is printing a dot.

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Every single second,
it's firing forget.

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Then, we're starting
a 100 other tasks

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which are the tests that
we actually want to run.

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>> I see. So what are we seeing
in the output here then?

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>> So in the output here,

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we'll see that a bunch

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of threads are starting
from the thread pool.

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This is.NET managing
our threads for us.

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>> Okay. Got it.

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>> We talked about before. So as
you can see, it's really slow.

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There's no weight in
between these two.

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So the second batch of a 100
tasks should already be running.

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But, because these are so insistent,

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they're running every
second for 100 tasks.

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It's really taking
a while to spin up.

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So we'll see once the thread
pool catches up here.

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We should start seeing these
tests firing off. There we go.

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>> There we go.

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>> So these are the tasks that we

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want and they're
running to completion.

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But, in-between, you'll see that

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the previous task fire and forget
are still printing their dots.

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>> I see. Got you. So
everything is all.

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Also, we see this garbage collection
going crazy a little bit.

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It's not very happy with us, yeah.

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>> No. This this isn't too
uncommon to be honest.

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We've seen cases in this
where the thread pool is

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just suffocated and no tasks
can start for minutes.

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Sometimes, if you use it incorrectly,

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it can get jammed up.

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>> Got you. So how do I fix this?

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>> So let's just restart

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the app to make sure that
those tasks are dead.

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>> Got you.

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>> Then, we'll go to the fix.

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>> Sure.

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>> So we do have the
tools to do this.

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We can have a bunch of long
running in the background,

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but what we need to do is
use Task.Factory.StartNew.

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This code inside is the same.

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We're just printing out those dots.

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But then, in the parameter
for creation options,

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you need to add
TaskCreationOptions.Longrunning.

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>> I see. So this is something
built-in to.NET task factory.

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What's the difference
between this Task.Start

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and task factory?
Start here, I guess.

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>> So Tasks.Run is actually

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Task.Factory.StartNew with
the default parameters.

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It's a shortcut for us.

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>> Got you.

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>> So Task.Factory.StartNew
is more fine-grained.

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We have a bunch of parameters.

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I added the link to the reference.

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>> Beautiful.

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>> There's a lot more
than we can fit in there.

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But, basically, when we set
a task as long running,

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it has a separate thread
pool that it's smart about

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and it'll be able to oversubscribe.

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You can read the documentation.
So let's take a look.

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This is the only change,
Task.Factory.StartNew.

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So we'll see, these are the
100 tasks that print dots.

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Our other tasks are already starting.

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>> Yeah.

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>> Just like that. We
didn't even have to wait.

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>> So previously, we
actually had a wafer.

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A bunch of them, all they get
scheduled. Everything happened.

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So now, we're actually seeing
things work as expected.

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From the very beginning,

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all the tasks were all
running concurrently.

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>> Exactly.

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>> The long running is
still continuing on.

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You've already completed those
100 tasks where before we sat

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for what like 20 seconds
waiting for it. That's crazy.

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>> Yeah.

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>> Very cool.

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>> It's insane.

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>> Well, Dean, this is awesome.

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Just so much great content
just packed in right there.

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>> Thanks, James.

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>> Now, of course, we'll put
all the links to the show in

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the show notes below for
all of the best practices,

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documentation, this
sample code, everything.

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You can also go to
aka.MS/xamarinbestpractices

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to find out more about all
of the best practices in

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Xamarin for the mobile CAT
Team which is super awesome.

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Dean, thank you so much
for showing this all off.

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>> Thanks for having
me on the show, James.

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>> Absolutely. Cheers. Make sure

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you follow the Xamarin
Show at YouTube,

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Channel Nine. You know where to go.

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Hit that notification bell,

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I'm James Montemagno This is

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The Xamarin Show, and
thanks for watching.

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>> Hey, James here.
Just wanted to check in

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and thank you for
watching this video.

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Now, do all the things that you
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While you're here, check out

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