Writing Energy Efficient Code, Part 2 

Session 712 WWDC 2014

Go in-depth into specific API and design patterns you can use to avoid consuming excessive energy as well as tools that can help you diagnose issues.

Hello, everyone.

I assume you guys are all here because you care about battery life.

And if you don’t, well, I got your bosses to thank because they’re probably the ones that sent you here today.

Well, either way, thank you so much for coming to the second half of Writing Energy Efficient Code.

My name is Albert.

I’m an engineer on the iOS Software Power team.

And today, I want to talk about how to apply some of the energy concepts and principles that, you know, was discussed in the first session to the various different technologies and features you might be using in your application.

So, last year we introduced the energy menu in OS X Mavericks, and this year we’re introducing the Battery Usage Menu in iOS.

Now, this menu aims to break down your iOS device’s energy and battery use by application.

Both of those menus will help educate as well as provide our users with information on where their battery has gone in their devices because we know that our users care about battery life.

According to surveys, one of the top reasons that would prompt someone to spend money to buy a new phone is better battery life.

So, our users do care about the battery life of their devices.

And with both of these menus, our message is clear.

We, at Apple, also care about battery life.

We go to great lengths and efforts to ensure that our laptops and mobile devices have some of the best battery life in the industry and we do that because we know that great battery life is a key part of great user experience.

Now, as a developer myself, I know that oftentimes schedules are tight, right?

Requirements are always changing and getting features and functionalities to work is your top priority.

However, what I hoped to show you today is that by keeping energy in mind, as you design and architecture applications, you might actually be able to simplify your development cycles.

I hope that you will be able to walk away with APIs or ideas on how you can minimize and reduce the energy use of your applications, and really, my goal today is to help you prevent your application from going up to the top of our battery list unnecessarily.

So, through the next hour, we’ll go through a quick recap of what Anthony has discussed in the first session and then we’ll talk about how to apply some of those principles to networking.

After that, I want to show you how you can actually measure the energy usage of your application through some tools that we have, and then we’ll camp on the idea of sleep for the rest of our session.

So with that, let’s begin our session with a quick recap.

So, in the first session, for those of you guys who weren’t able to attend, Anthony briefly talked about two energy concepts that really anchor energy efficient coding.

First is the idea of fixed cost or what I would like to simply refer to as the overhead cost.

Resources on our system, by default, stay in idle state and this is to conserve power.

Now, when your app requests to do some work, the system will need to power up that resource.

We need to keep the resource up while you’re doing your work.

And then most resources go through an intermediate state where the resources are kept up in case some other work needs to be done very shortly.

Now this is so that you won’t have to pay or wait for the resource to boot up again while you’re doing-while you’re doing your work.

But the system does stay up a little bit-the resources stay up a little bit even after you finish your work.

And finally, when the resource decides that there’s no more work to be done, it’ll go back down to idle state.

So, as you can see on the screen here, the area in the green is, you know, the work that you’re doing in your application, but the area under in blue is the fixed cost or the overhead cost.

And there is these intermediate stanzas between where the resource is still kept up while you’re not doing any work.

So, if you want to minimize the energy used for your applications, you’ll want to do as much work as you can while you do have the resource so you can minimize the overhead cost of doing your work.

Second is the idea of trading power for energy.

Now, a lot of resources on our systems have different power and performance states and that’s to conserve power while still ensuring that we can provide fluid performances.

We all know, hopefully, that energy is a factor of both the power used as well as the time it takes for you to finish your work.

As you can see on the screen on the figure on your right, the idea here is that by doing as much work as you can-although, you could potentially be using a lot more power instantaneously-you’ll be able to finish your work quicker, minimizing the overhead cost as well as the overall energy used.

Essentially, you’re trading power for time to reduce energy.

So, that’s trading power for energy.

Now, as developers, I know that these concepts can be kind of abstract and hard to apply when you’re actually coding.

So, Anthony boiled it down for you guys.

Here’s what reducing energy use really comes down to and that’s to do it never, to do it at a better time, to do it more efficiently and to do it less.

You’ll want to do work never, do work at a better time, do work more efficiently and do work less.

That’s what reducing energy really comes down to.

Now, Anthony went into great detail on how to apply these principles to minimizing the system activity of your applications in reducing-essentially, reducing the CPU usage.

So, let me just quickly go over that for you real quick.

For doing it never, Anthony talked about reacting to app transitions, right?

If your application is going into the background or is not going to be the frontmost app, make sure you stop any unnecessary work, such as any type of rendering because your users will not see it.

Now, for doing it at a better time, Anthony talked about two scheduling APIs that you would consider using and that’s the NSBackgroundActivityScheduler for OS X and the NSURLSession for both iOS and OS X to schedule your network transactions.

Now, we’ll talk about NSURLSession a little bit more later.

For doing it more efficiently, Anthony talked about the new quality of service APIs and he really went into detail on how you can set the appropriate quality of servers with the priority of your NSOperation or GCD queues so you can do your work more efficiently.

And finally, for doing it less, Anthony mentioned the importance of coalescing your timers, right?

You want to coalesce your timers to let your system, your CPU idle as much as you can.

Now, before I continue, I wanted to take a quick detour and talk about something new for iOS.

Now, up until now, we’ve seen many developer bugs where their applications that are running in the background are utilizing a lot of CPU for an extended period of time.

This should be considered bugs because there are pretty clear guidelines on why and when an iOS app can run in the background.

So, as you help developers catch these bugs, as well as minimize the battery impact on the device when this happens, we’ve implemented a CPU monitor that will kick in when your applications are running-are considered background running.

Now, what this will mean for your applications is-well, it really shouldn’t mean anything, right?

The CPU limits that we’ve set are purely meant to catch runaway usage.

They’re set at a limit where if you’re doing the normal type of work that you’ve requested according to the background modes that you have in your applications, you should not be affected in any way.

However, if you do end up hitting the CPU limit, your app will be terminated and a log will be generated to help you identify that this has happened.

Here’s what this log will look like.

So, up top, you’ll see that the way to identify is the exception type, which is EXC-RESOURCE and the subtype, you’ll see CPU-FATAL.

This is how you’ll know that your application that was running in the background was terminated.

And on the bottom, we’ve included some microstackshots of what your application was doing right before we terminated it.

This should help you identify in your CodePath where you had your runaway CPU usage so that you can fix it.

So this is really-now, this will not only preserve battery life but it will help our developers, which is you guys, to catch bugs that you might not have known.

So once again, this is new and we’ll begin in iOS 8.

So, let me go back to the recap-and I wanted to mention one last thing that Anthony talked about and that’s really on energy-an energy efficient way to do graphics and animation.

And the two points that he talked about were to avoid extraneous screen updates, right?

Don’t be updating the screen when it’s not necessary and to review the blur effect usage.

Now, blur is a great way to include depth as well as, you know, to provide layering effect for your UIs.

However, with all great things, they can cost more.

So, you’ll want to review, you know, all the animations or frame changes that you’re doing behind your blur and try to minimize them as much as possible so that you can provide your users with a great UI while helping them conserve their battery life.

So, that pretty much sums up our recap.

If you have any questions about what I just, you know, breezed through, feel free to swing by our labs this afternoon.

You know, once again, we have one at 2 o’clock in the Core OS Lab and tomorrow at 3:15.

Anthony, myself, as well as our colleagues, will be happy to answer any questions that you may have or check out the video when it becomes available.

Anthony really goes into great detail on all these things that I just, you know, quickly talked about.

So, to begin our session today, I want to start by talking about networking.

We live in a time where the way we get information, the way we shop, the way we connect with friends, or the way we backup important data, or, you know, memories, is really through networking.

I go as far as to say that there’s probably very few apps in the App Store that don’t do any networking and so it’s important that we discuss how we can do networking in an energy efficient way.

So, let’s start with a very generic example.

Let’s say today your requirement is to develop an application to send some data to your servers.

So, an easy way to do this and the most intuitive way to do this would be, right when data comes we’ll, you know, go ahead and send it off to the servers, right?

So, as you can see as data is coming in, we’re firing up, we’re setting up connections, sending into our servers.

Let’s see what the energy cost looks like for doing this.

So, here you have a couple of data syncs coming in, right?

And let’s assume that the data that you’re sending is small so you think to yourself, “Well, I’m just, you know, sending, like, small packets up to our server every once in a while.

It’s probably not going to use that much energy, right?”

Well, given what we just talked about in overhead costs, by default, the radios on our system are idle and the radios are the resources that you’re going to utilize to send your network, to send your packets to your servers.

So, in order to send these data packets, the system has to bring up the radios, keep the radios up while you’re doing your work.

And then, if you take a look at the transfers happening to your left, you’ll see that, you know, like we said, even though there are times where you’re not actually sending the packets out, the radios are actually kept up.

This is the overhead cost that we talked about earlier.

And then, if you look at the transfer on your right, even though you’re only sending one small data packet, you’re still paying the cost to bring the radios up for you to do that, right?

So, there’s a big overhead cost in using the radios.

Now, not to complicate things, but depending on which technology you’re using to do your transfers, the cost of both the time out as well as the energy used can vary greatly.

All right, to give you guys an idea, if you’re simply web browsing constantly on an iPhone 5S, if you’re doing it through Wi-Fi, your battery will last about 10 hours.

However, if you’re doing this through 3G, it will only last you about 8.

So, the technology you utilize to do your transfers will affect the energy used in your network transactions, right, whether you’re on Wi-Fi, or cellular, or even, you know, different cellular carriers kind of impacts the energy you use through your networking.

Not only that, your network condition, your signal strength as well as your network throughput can impact the time it takes as well as the energy we use to send off to your network transactions.

Networking can be quite expensive if not done intelligently.

So, let’s go back and take a look at our simple web server example, and this time instead of sending in one at a time, let’s implement a simple buffer.

So, let’s buffer the data on our device before we send it.

Now, instead of paying the overhead cost to send each of those packets, your energy will look something more like this.

As you can see while you’re accumulating data, your radio-the radios get to stay idle and so you’re not paying the overhead cost.

And once you do need to send a group of data, although you do still need to bring up the radios, it’s not-it’s a lot more worth it now, right?

You’re sending a lot more data while paying less of an overhead cost or actually-sorry, you’re sending the same amount of data but paying less overhead cost.

So, it’s important to know that the way you schedule your network operations can greatly impact the energy use in your application.

So, let’s think about how we can apply some of the principles Anthony talked about earlier to the networking you’re doing in your application to help reduce this energy.

So, for doing it more efficiently, we just looked at the importance of coalescing your transactions, right?

By doing more at once, you’re paying less of an overhead cost and you’re reducing the energy used by sending the same amount of packets.

Now, for doing it less and never, it’s simple.

Cut down your transfers, right?

The best way to conserve energy is to do less work.

So think about you-think about creative ways that you can reduce the data sizes in your application.

If you’re sending media-like, let’s say you’re uploading a photo to a social media website.

And, you know, if the photo is never going to be displayed at its full quality, consider reducing the image quality first before you send it out to your servers.

Compression is also another easy way.

If you’re sending files, compress that file before you send it up to your servers to reduce the amount of data that you’re sending.

Now, on top of reducing data sizes, make sure you think about-make sure you try to avoid, as much as you can, redundant transfers, right?

And make sure you cache information that you’ve already downloaded.

This will not only help you save energy but it can also improve the performance of your application, right?

Since the next time you need an asset, you don’t have to wait for it to be downloaded again.

It will already be readily available.

Also, use resumable transactions.

Especially on mobile devices, network connections can go in and out fairly frequent, so you want to make sure you’re using transactions that can be paused and resumed.

So, if you detect the network condition is bad, you can pause, and you don’t have to resend those chunks of data that was lost when you do get to send them.

Now, finally, with networking conditions, you won’t-you want to make sure that you handle your network errors properly, right?

And make sure you have good timeout or retry policies.

It does not make any sense for you to continuously try to send data to your servers when you can’t.

So, these are just some of the things to consider on how you can reduce the data sizes of your network transactions.

Finally, for doing it at a better time, we have consider tolerance.

Basically, you want to understand the requirements of your application.

Is this network-does this networking transaction need to happen immediately, right?

As we’ve just looked at earlier, the technology we use as well as the signal conditions can greatly impact the energy use of your application when you’re doing those transactions.

So, if the-if the conditions aren’t ideal, can we wait on this network transaction?

You know, this is especially important for larger downloads such as, let’s say, you’re backing up a user’s data or, you know, you’re downloading a movie that probably is just purely meant to be put in the user’s media library.

Those things won’t have an immediate user impact and so consider doing those at a better time.

And we’ll talk about NSURLSession more later on an easy way to do this, but let’s take a look back at our example first to see how we can apply some of these principles to help reduce the energy of your network.

So, we already determined that by buffering your data, you greatly reduce the overhead cost.

Now, let’s implement a simple check on the device to make sure that the data is actually relevant.

Let’s say you simply diff the current data versus the previous to make sure that something has actually changed before you send it off, right?

Now, I have been able to reduce the data size of my transfer and finally, let’s make sure that the signal conditions are good before we send it off, you know?

And then, obviously, here I’m assuming that this data is not needed immediately, so there is some tolerance before I need to do this transaction.

Now, by implementing these three things, I’ve been able to save a lot of energy while still providing the data that needs to be provided.

So by now, I mean, a lot of you guys are probably asking like, “This is not easy at all, right?

Especially with signal conditions, especially with retries-like, this is not an easy thing to implement and it kind of goes way over my head.”

Well, this is where I’ll talk about NSURLSession.

This is an API that will allow you to easily integrate pause and resume as well as implement caching with NSURLCaching.

Now, one of the good features in this API is, as Anthony has mentioned earlier, the ability to create background sessions.

So, with background sessions, you’re actually able to do your downloads out of process.

And this is especially important for iOS apps because your application won’t get to run all the time, right?

So with background sessions, you no longer have to rush to download everything you want immediately.

You just simply-you can create a background session and allow the system to do that for you and your app will be alerted whenever the transactions are done or if it errors out.

Now, within iOS, when your applications are moved to the background, these background sessions will actually also automatically opt-in to throughput monitoring as well as automatic retries.

So, those are some things that will be automatically taken care of for you in iOS.

Now, one of the features that Anthony mentioned, and I’m going to once again stress the importance of-for you to consider using this as the discretionary flag, right?

You can set for your background sessions, you can set it to be discretionary.

And by doing this, you’re basically telling the system, this is one of those “let’s do it at a better time” type transactions.

The system will automatically know that this isn’t needed immediately and find the most power optimal time to schedule your network transactions.

And all of this is transparent to your app, so you don’t need to know anything about it.

You’ll simply get alerted when the transaction is done or if it errors out, right?

Anthony also mentioned that you can adjust the scheduling window.

You can give the system a certain amount of time that you want this transaction to occur.

And, generally, you want to set it to be over 12 hours to allow the system to actually be able to schedule it since, you know, networking connections can go in and out and the user can be using their devices.

But, you know, make sure you set this to over 12 hours and the system will do its best to schedule your network transaction within this time window.

Now, if it is unable to, an error will be thrown and then you can react accordingly.

For instance, you know, immediately try to do your networking transactions or, you know, once again schedule another one, giving, you know, another window for you to wait if this transaction can happen at a later time.

So, here is a code snippet of what this may look like in your application and it’s quite simple, right?

All you have to do is make sure you set up your configuration.

So, here I have a background session configuration setup.

And, you know, here I can set some flags.

For instance, I only want to do this when users are connected to Wi-Fi because I know that that’s more power efficient.

And also I want to save my user’s money because obviously data costs money.

Then we set our discretionary flag, right?

So this is where I tell the system, “You take care of downloading this at whatever time you think is best.

Just tell me when it’s done.”

And then I say, “I want it within the next 18 hours.”

Now, you just have to create your session with the configuration that we just created.

Create task and send it off.

That’s it.

The system will now do all the downloading for you in an energy efficient way and all of this is transparent to your application.

So, this is really a great API for you to do your networking transactions in an energy efficient way.

For more information, you know, check out the “What’s New in Foundation Networking” video when it becomes available or swing by the networking labs.

But let’s sum up networking, right?

Essentially, networking comes down to these three Ts, all right-to coalesce your transactions, to cutdown your transfers, and to consider tolerance, right?

So keep these three things in mind as you are designing how you’re going to schedule your networking operations to minimize the energy use of networking.

So, we talked a lot about different techniques and, you know, APIs for you to be able to reduce the energy use of your application.

How do you know that you’ve actually achieved that or how can you actually measure and profile the energy use of your application?

I hope that’s the next question that you’ve thought of because that’s what we’re going to talk about.

So, on for OS X developers, you could do this directly through Xcode, right?

In the Xcode debugger, as you can see, there is this little energy section here that can really help you kind of understand, at least to some extent, the energy impact of your application as it’s running.

For iOS developers, however, you will not be able to use Xcode to do this.

What you will be able to do is to pre-record a trace of-you know, let’s say you want to profile some activity, you can record a trace of the system’s energy usage as well as some other information, and then you can use the Energy Diagnostics tools and instruments to help you visualize what’s going on.

To record this trace, simply navigate to the Instruments menu and this is in Settings Developer menu.

You’ll see an Instruments menu that you can select and simply click Energy.

And, you know, selectively you can choose to record networking information as well and just hit Start.

Now the system will begin recording your traces and you can just simply navigate through your application, do whatever work you wanted to do to profile it.

And then when you’re done, come back to this menu and hit Stop Recording.

Now your traces are recorded.

I do want to mention there’s a little subtext right there.

I don’t know if those of you in the back can see this, but basically, we’ll only save one trace at a time.

So, if you click Start Recording again, your previous trace will be erased.

So, keep that in mind.

Now, you have your traces recorded.

Simply connect your device, you know, to your Macs, to your laptops.

And then through the Instruments Energy Diagnostics menu, you just have to click Import Data from device.

That’s what that, you know, highlighted blue selection is.

And then your traces will be-you’ll be able to pull up your traces on instruments with the Energy Diagnostics tool.

So, I’m going to go ahead and show you guys what this may look like for an iOS app.

So, this should help familiarize you guys with the energy diagnostics tool that we have to help you, you know, kind of visualize the energy impact of your apps.

So, as you can see here I prerecorded two traces that I’m going to show, but let’s focus on this first one here.

So, up top of energy diagnostics we have energy used, right?

And this really tells you the system energy as your application was running.

And if you look at the details page on the bottom, it might be hard to see, so, let me see if I can zoom in on this-Great,there you go.

So, you’ll see that energy used is, you know, really an instantaneous reading based on one to 20.

Twenty means you’re using a lot of energy and one means you’re using very little energy.

So, you can see as I’ve recorded this trace about-for about, let’s see, 13 minutes-you’ll be able to see that energy is, you know, generally pretty high.

What I’m doing here is every about 30 seconds, I’m firing off a network connection, right?

Here to the Connections tab, you’ll see all your connections.

And you can actually even see CPU activity, right?

So, CPU is fairly active since every 30 seconds I’m firing up network connection.

Now, to help you better debug, you can also-you also get information such as network activity.

So, you’ll be able to see, you know, how many bytes you’ve transferred from your application, what technology was going through and, you know-let’s see, as you can see here, you have your cellular.

You have Wi-Fi.

All right.

Let’s come back out.

And then, we also give you information such as Display Brightness.

Now Display is also an area that can use up a lot of energy so you’re-so, if your application is, you know, pushing the display up all the way to its full brightness, make sure you disable that feature when it’s not needed.

But here my display is about 20 percent brightness, might-and we give you sleep-Sleep/Wake information for your iOS devices.

So, if your device was asleep, we’ll still be able to show that here and it will look something more like the dark red area here.

And then there’s Bluetooth, Wi-Fi and GPS.

Now these three are purely on an on and off.

We only show you if it’s on or it’s off.

So, this is energy diagnostics.

It’s really a good way for you to see the system energy, what was going on in the system when your application is running.

Now, just to show guys the importance of coalescing your transactions, I’ve recorded a second trace where instead of every 30 seconds, as you can see here, I’m only firing up connection every about two to three minutes here-two minutes.

So, as you can see, you know, it looks like I’m sending a lot more data.

However, if you look at the energy usage here, and let’s zoom in, our previous trace, our energy usage was pretty much stuck around-let’s see if can get this to zoom in…there you go-stuck around 14, 15, 16, throughout the whole trace.

However, simply by coalescing my transactions, now the energy usage of my application, there you go, you begin to see some like sixes, sevens, and eights, right?

And then when you are firing your transactions, once again, the energy usage will go up to 14, you know, 16, 17, but it comes back down again.

So, it is important to coalesce your network transactions and this is energy diagnostics.

It’s really a great way for you to visualize the energy use of your application.

So, we’re about half way through our session and we talked about energy efficient networking, applying some of the principles through the networking you’re doing in your application.

We talked about how to use energy diagnostics to measure the energy impact of your application for iOS devices and iOS apps.

Next, I’m going to camp on the idea of sleep.

Now, what I’m about to talk about will be-the concepts that I’m going to discuss can be applied for OS X developers.

However, I just want to point out that the technologies as well as features I will be discussing more in detail are primarily on iOS devices, so keep that in mind.

Now, a wise man once said, “To sleep is to prepare for the longer journey ahead.”

Now, that’s true for you and me and that’s also true for our devices.

The battery life of our devices really depends on sleep.

Once again, to give you guys an idea on our favorite 5 or 5S-iPhone 5S like we saw earlier-if you’re doing constant web browsing, you know, the screen is on, right?

The radios are up, you know, you’re downloading and uploading packets, you know, the display is-the display is on like I said and you know your device is fairly active when you’re doing these things.

So, you’ll get about eight to 10 hours of battery life.

However, let’s say instead of web browsing, you’re simply just playing audio on your device.

All right now, the screen is off, the system is a lot less, you know, busy.

It’s probably doing some audio packet audio-it’s probably decoding some audio packets, running those to your speakers, but it’s fairly idle, so, you know, we get about 40 hours of battery life.

However, if your system is completely idle and asleep you can get about 250 hours of battery life.

That’s like 10 days’ worth of battery life.

Now, I know it’s not really practical for you to just look at this number because our users are not going to just buy a device, leave it on a table, hope it sleeps so they can get 10 days’ worth of battery life.

That’s not really useful at all.

However, the concept is simple here, right?

The longer you allow your devices to sleep, the better battery life it will get.

So, for our typical user, when they turn off the screen of their device, they either set it aside or put it in their pockets, they assume that the device is asleep, right?

They’re not interacting with the device.

It’s, you know, out of their sight.

The device should not be doing any work.

However, as developers, we know that that is not the case, right?

When the device is seemingly asleep, your apps are often waking up the device to interact with all these different technologies and features to provide their users with up-to-date information.

Now, this is necessary, obviously, because our users expect, you know, their emails to be coming through, our users expect the latest news to be there when they, you know, start using their device.

However, you know, every time you do work, you can pretty much expect the device needs to be awake and thus, even though you’re only doing a little bit of work, and here’s our favorite chart again, our favorite graph.

Even though you’re only doing a little bit of work, you’re pretty much paying the whole overhead cost of keeping the device awake.

And worst of all is all of this is happening transparent to our users.

So, if you’re doing a lot of work in the background while the-while seemingly the device is asleep, when the user turns on their device and wants to use it again, they’ll be very confused as to why their battery has drained and they will not be happy customers.

So, it’s especially important for you to minimize the energy use of your applications when they’re running in the background.

And, really, the best way to do that is to minimize the number of times your application has to keep the device awake, right?

Do as much work as you can so you minimize the number of time you’ll need to be doing that work.

So, for the-with the remaining time that we have, I want to talk about these four areas in Notifications, VoIP, Location and Bluetooth.

I want to talk about some of the best practices as your applications are utilizing these technologies when it’s running in the background.

So, first, from notifications.

Notification is a great way for your application to send, you know, to just alert the users of some information.

Now, it is important for you to know, however, every time you either schedule a local notification or send a remote push notification, the device will have to wake up to display that for your users.

So make sure you use those carefully.

If you’re constantly sending or scheduling local notifications or sending remote notifications from your servers, pretty much the device-the user’s device will be awake for a majority of the time.

Now, one thing that you guys might not know is with the push notifications you send, you can actually set a push priority.

You can actually set a bit that will determine the priority of your push.

Now, by default, your pushes are sent with priority 10, which is deliver this immediately whenever you can, so our servers will attempt to do that.

However, if you’re simply trying to notify or alert the user of something that is not needed to be displayed immediately, consider setting your priority at five.

This will tell our servers to, you know, send this push maybe at a better time for your device.

For instance, let’s say another immediate-another high priority push is coming through, then let’s just go ahead and send this push through with the high priority push.

But it won’t actively send it unless it’s a power optimal time.

So, consider using this for your push notifications.

Now, one thing we do want you to start using notifications for is VoIP.

Now, this is an area where we’ve made great improvements in iOS 8.

So, when VoIP was first introduced in iOS, we required the VoIP apps to maintain their own persistent connections.

This meant that periodic keep-alives had to be sent from your servers to the VoIP app and vice-versa.

Now, if the device was asleep, the device will need to wake up for your applications to be able to respond to these keep-alive packets and this meant periodic wakes.

Not only was this bad for battery life but it also made developing VoIP apps fairly complex, as some of these algorithms to manage our connections can be very, very complicated.

To simplify the development process as well as conserve the battery life on our systems, in iOS 8 we’ve introduced a new way to do VoIP and that’s VoIP through the PushKit framework.

This new VoIP mechanism allows you to communicate with your VoIP apps through the Apple’s Push Notification Service, right?

In this way, you no longer need to maintain your persistent connections.

Meaning, you won’t have to constantly wake up the device just so that your connections won’t timeout.

Now with these VoIP pushes, your app will be allowed to receive runtime to process these VoIP pushes.

So your app will get runtime whenever a VoIP push is sent to your device.

And the best of all is your apps will be able to do this even if the user terminated the app or for any reason your app was terminated.

[ Applause ]

Thank you.

Someone’s enthusiastic about this.

And this is great, right?

Previously, in iOS, if a user terminates your VoIP app, the connection is gone and you’d no longer be able to communicate with that device, your servers won’t be able to communicate with the device anymore.

Now, we will do that for you and so even if the user terminates your app or for any other reason the app terminates, you will still be able to communicate with your apps using these VoIP pushes.

And finally, to help with performance as well as to improve the call setup times, we’ll allow you to include up to a 4k payload in this VoIP pushes.

This is a lot more than the 256 bytes you get with regular pushes.

So this should help improve the performance as well as the call setup times of your applications.

Now, to adopt this new framework, what you’ll need to do is link the new PushKit framework, it’s new in iOS 8, and then you want to register your app to receive these push notifications, these VoIP pushes.

So, you’ll do something like this in your application, didFinishLaunching delegate.

So, you want to create a PKPushRegistry object and then set the delegate to yourself.

And we’ll be implementing two delegate methods in a little bit.

But the main thing is you want to set your desired PushTypes to include VoIP.

And with these three simple lines of code, your app is now registered to receive VoIP pushes.

I do want to remind you guys with all-as with all background running modes, you will have to make sure your app has the VoIP background remote requested.

So, now, let’s talk about the two delegate methods that we’re going to implement.

First, similar to Remote pushes, you have to handle the push token that’s given to you.

Now, if you have both the Remote push as well as the VoIP pushes in your applications, you will get two separate push tokens.

So, you’ll need to send both of those up to your servers so you can communicate with your app.

And then you have the delegate to handle your incoming push, right?

So this is where your app will get-will start running when a push comes.

So, here you can send off your notifications to your users-you know, maybe it’s the new interacting notifications that you want to display, right?-to alert the users that a call has come in.

And here, you know, you could probably begin to set up your connections with your servers to begin establishing your calls.

So, that’s all you need to do on the device side to adopt this new VoIP mechanism.

Now, on the server side, you’ll still need to be required to do some more changes, right?

First, you want to go and request the new push certificate for VoIP and you can do this through the Apple’s Developer Portal.

And then, simply send your pushes with the token that you got and this new push-VoIP push certificate that you have.

Now, one thing to note is this mechanism will only work with devices running iOS 8.

So if you try to send these VoIP pushes to devices running iOS 7, it will not work.

So you need-you’ll want to make sure that you maintain some type of compatibility on your servers.

But this is a new way that we’re introducing for you to do VoIP communication with your applications and this is new in iOS 8.

All right, next, I want to talk about Location.

Location is a great way for you to include context in the information you provide for your users, right?

Knowing where users are or users have been will allow you to provide better suggestions, more relevant resources as well as location-specific information that could be immediately useful for your applications.

For my wife and I, one of the most commonly used features we use on our phone is the location-based restaurant suggestions, right?

That really helps us to be able to procrastinate in deciding what we want to eat.

So, Location is a great tool to integrate in with your applications.

However, getting a user’s location can be unnecessarily expensive if you’re not using the right APIs.

So, I’m going to talk a little bit just to whet your guys’ appetite on a couple location APIs that you can consider using, and I’m going to first start by talking about continuous location updates.

So, the continuous location updates is a great way for you to get fine-grained user data, fine-grained information about where your users have been.

Now, there’s two things I want to point out here.

First is that using continuous location updates can prevent your device from going to sleep.

Whenever you call startUpdatingLocation, the location hardware will immediately begin to stream location data for your application.

Now, if you have the location back on a running mode, the device will have to stay awake even if your app is not active to allow your app to process this location data.

Now, if this location data is coming in frequently enough, usually because of the accuracy that you sent, your device will be kept awake the whole time and you’ll be paying the overhead cost of keeping the device up while you’re receiving these updates.

Second, I talked about accuracy.

Accuracy makes a difference, right?

Depending on the accuracy level you set, not only does this affect the frequency but core location uses different technologies to get a user’s location to you.

Depending on the accuracy level you set, you will utilize different technologies and so it will have varying amounts of cost to get the user’s location.

And, in general, the more accurate you request, the more energy it’s going to be required on the location hardware site to get that information for you.

So, know that continuous location updates, especially a high accuracy, can be really, really expensive, so you’ll only want to use this if it’s necessary, right?

And make sure you, you know, turn off continuous location updates whenever it’s not needed.

If you won’t be needing to process user’s location data immediately or live, if you’re not going to be providing users any feedback with the location data that you get back, consider using some of the other more power-friendly APIs that will still alert you of users’ locations when you are interested in them.

And one of those is deferred location updates.

So, this is a great API to use if your app requires GPS level of accuracy but won’t need to process that data live, right?

What happens here is that the location hardware will buffer that data before it gets sent to your application.

Now, you’ll still be paying the cost of utilizing, you know, in our case since you’re requesting GPS level of accuracy, the GPS.

However, you will allow the device to be able to go to sleep for longer periods of time.

And this is a great way to, you know, save energy while still being able to get that fine-grained user location that you want.

So, if your application, let’s say, wants some type of historical information like, let’s say, a run track app or maybe you’re implementing some type of life tracking app, you want to consider using this because this will still give you that fine-grained continuous location data that you wanted but at a lower cost.

Now, if you don’t need GPS level of accuracy, consider using the Significant Location Change API, right?

This API will signify the location hardware to only notify your app if the user has moved, you know, a certain amount of distance.

And this is, you know, you can expect pretty much updates to come in, at least, when users have traveled over 500 meters or there’s also a rate limit of five minutes.

So, this is a great API to use if your application is-needs to update information based on regions.

For instance, a weather app, or let’s say you want to provide your users with the nearest local attractions, right?

And you want to use significant location change because now your device does not have to wake up as frequently.

And finally, I wanted to mention region monitoring.

This is a great API to use if your application only cares about when users are entering or exiting out of a specific location, right?

You want to use this, let’s say, if you’re developing an app, let’s say, of a museum, right?

You want to-when the user gets closer to your museum, you want to, let’s say, update the app with the local attractions that might be there.

You want to use a region monitoring to set up a region that you’re interested in.

Once you do that, you can happily allow the device in your app to go sleep while the location hardware will check for you if you get closer to that region and only wake up your app when you do.

So, once again, all these are great APIs that will help you reduce the amount of time the device needs to stay awake.

Oh, one more thing about location.

Please, please remember to stop your location updates when they’re not needed.

I can’t tell you how many times we’ve, you know, received battery complaints only to find that, you know, some application forgot to unsubscribe to their location updates when they’re not needed.

Please double check, triple check, because location updates can be expensive and it can keep your devices awake.

So, please don’t forget to stop your location updates when they’re not needed.

So, I’m going to go through a quick example of what this might look like for your application.

So, let’s say, today you’re developing a run tracking app and your requirements are when the users are running, you want to keep track of their route.

And, you know, also you have this local store that you want to update your app whenever the user gets close to that store to send the latest coupons or discounts, right?

You want to entice your users to go into your local store.

So, one way to do this is to use continuous location updates.

Now, obviously, right, when you’re doing continuous location updates, in your code it would probably look something more like this.

Whenever I get a location update, make sure I store if the users are running.

If the users are not running, then you can drop that location data.

Also, I want to check, every time I get location data, if I’m close to my local store, right?

That way I can update the device with the new coupons so that your users will want to go to your store.

So, let’s take a look at what this will look like for your device.

As you can see the device is on even though, you know, the users have no idea that this is on and you’re utilizing the GPS, so location hardware is on.

Now, as the user starts running, right, you’re constantly updating the route but your device has kept on for the whole time.

And then, let’s say the user stops running and now they’re walking, walk-slowly walking.

You’re checking and checking and finally, you get close to your local store and you can update your coupons.

And so, as you can see, both the GPS hardware and the device is kept on the whole time while you’re doing this.

Now, let’s use some of the location efficient APIs to do this, right?

So, now, instead of using continuous location updates, let’s set up the deferred location updates as well as the region monitoring.

So, first thing this will do is it will, kind of, clean up your code a little bit, right?

In your region monitoring delegate, all you need to do is just-you know, in that function whenever you get that callback, just simply pull your server from the new coupons.

And then you have your location callbacks, and in that function all you need to do is basically take that chunk of data that the location hardware has buffered for you and, you know, simply store it if the users are running.

So, with that, let’s take a look at what this does for your device.

So, as the user is running, the device is asleep until oh, I’ve run this long a distance.

So, now, I can opt in my route when the device is on.

And then, you know, the device can happily go to sleep while the user continues to run and then oh, significant distance have reached, let me once again get this data.

As you can see just from now, you have already reduced the amount of time that the device needs to stay up and thus reducing the energy cost.

Now, the users are done running so, you know, we don’t need continuous-we don’t need deferred location updates anymore.

So, let’s stop that.

And then as users are walking, walking, walking, oh, now you reach and monitor API will kick in and alert your app and then your app can wake up to respond and to get the latest coupons, right?

These location efficient APIs are a great way for you to get the same location data that you might be wanting, but more energy efficiently.

And so, I talked about a couple.

There’s also something I did not talk about.

There’s the iBeacons here and AutoPause.

I didn’t really have time to talk too much about.

But there’s a great document online that will allow you to get best practices on what to do, which APIs to use when you’re using location.

And also new in iOS 8, I wanted to mention there is a significant location visited API.

So, if you didn’t get to check out the core location session yesterday, you’ll want to check out what’s new in core location.

All right, so last, I wanted to spend just a little bit of time talking about Bluetooth.

So, with the advancement of Bluetooth low energy, Bluetooth accessories are now becoming increasingly popular.

And with Core Bluetooth introduced in iOS 5, it’s now easier than ever to integrate Bluetooth accessories with your iOS app, right?

This will allow you to provide rich features such as health monitoring, right, the new health kit.

This will allow you to provide information for users that will allow you to do fitness and activity tracking as well as, you know, item proximity sensing.

So, we could probably spend, like, a whole ‘nother hour here just talking about how to-what are the best practices on how to communicate with Bluetooth accessories, you know, what’s the best way, what’s the most energy efficient way to design and architect the communication.

But, due to the amount of time that we have left, I simply want to mention one thing, and that’s whenever you do Bluetooth transfers, your device will wake up for your app to be able to receive it even if your app is running in the background.

So, whenever I say that, hopefully by now, alarm bells begin to set off in you heads, right?

“My device has to wake up for my app to be able to receive this data.”

And, hopefully, this chart somehow just, you know, pops up in your head once again, high overhead cost, device wake, not good for energy.

So, you want to think about creative ways to minimize that.

So, once again, to help you guys just kind of get some ideas and visualize this, we’re going to go back to our running app and let’s say we integrated a Bluetooth fitness band, right?

You now want to help track user activity as well as perhaps heart rate, you know, blood pressure when the users are running.

So, you know, we’re going to use an example that we’ve used over and over again, and hopefully, this idea will stick in your head, right?

We’re going to start by just streaming the data.

All right.

So, now your fitness data are coming in and the device wakes up.

However, because you’re constantly streaming the device can potentially be kept up the whole time while data is coming in.

So, our favorite solution is buffering, right?

So, now, instead you’re buffering the location data on your accessory site and so your device doesn’t have to pay the cost to stay awake.

And once your buffer is full, then you spend one time-then you do, in one time, to send all your data over to your device and the device only has to wake up one time to process a lot of data and then it can go back to sleep.

Right, this is-this is something we really want you to consider, especially when you’re not really actively providing users with information immediately, right?

In our running tracking app, this works because, you know, our users probably won’t be checking their devices all the time when they’re running.

So, you can coalesce your data transactions, doing more work at once, so you can minimize the number of times you need to keep the device awake, right.

You don’t want to implement a cool fitness band that’s going to constantly keep the users’ device awake even when they don’t care about the information.

Because then the users are going to put off their device, you’re going to see that little energy drain bar and when the user wakes up their device, they’re not going to be happy.

So, the best way really to reduce the energy cost of your application when it’s running in the background is to do as much work as you can when you do get to run so that you can minimize the number of times you have to wake up, right, and to coalesce your work so you can cut down your wakes.

So, let’s take this one step further, right?

So, we’ve talked about this run tracking app and we know that, once again, we’ve implemented a buffer on the Bluetooth side, but we’re also implementing using the deferred location updates, right?

So, these-both of those have greatly minimized them for wakes, but we can even do better.

So, let’s say, now instead of having these two channels of waking up your device, let’s coalesce them.

So, as users are running, you’re gathering data on your fitness band.

But then, deferred location updates wakes up your-wakes up the device in your app and says, “Hey, you have location data.”

While your device is awake, let’s just go ahead and grab the data from your fitness band so you no longer have to wake up the device again when you have your buffered data.

Then your app can process all these things at once and go back to sleep, helping you conserve energy.

So. once again, the best way for you to reduce energy use of your app when it’s running in the background is to coalesce your work so you can cut down the wakes.

Cut down the number of times you’ll need to wake up the device.

And especially in iOS, most of the time you’re running in the background, you’ll only be doing a little bit of work for short amounts of time.

So, you want to minimize the number of times you do that so you can help produce energy.

So let’s sum it up, right?

And I want to leave you guys with this quote.

Hopefully, you guys are all familiar with this: “With great power comes great responsibility.”

We’ve provided many tools and APIs for you to, you know, build these amazing apps.

Use those responsibly, right?

Keep in mind energy as you design your apps because it greatly impacts user experience.

Find creative ways in your apps to do work less or never, to do work more efficiently and to do work at a better time.

And finally, like we talked about, be a considerate background app.

Your users have no idea of what you’re doing when you’re running in the background.

So, be considerate.

Think of ways to coalesce your work so you can cut down the number of wakes.

So, for more information, we have here Paul and Jake as our evangelists that you can contact.

And also, here are some related sessions that might be and-that you might be interested in.

Now, some of these have passed already so I would recommend you to go download the videos, right?

For the graphic and animations, it really goes into details about, you know, how to-how the graphic rendering pipeline works and how blur works.

And then you have, obviously, “What’s New in Core Location” as well as “What’s New in Foundation Networking.”

And then you have the instruments, “Improving Your Apps with Instruments.”

Also, like I said, download Anthony’s talk earlier.

Thank you so much for coming.

Enjoy your lunch.

[ Applause ]

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