Writing Energy Efficient Code

2014 Session 710 & 712

What Uses Energy?

Concept

Coalesce work

Cut down wakes

“To sleep is the prepare for the longer journey ahead”

Preview

Do It Never

Do it never

• Avoid unneeded work

Respond to changes in active state

Do it neverLocation

“Stop Location Updates”

Do it at better time

• NSURLSession Background Session

• Understand requirements

• Overhead cost

Let the system schedule work

Do it at better timeNSURLSession - Discretionary Tasks

Do It at Better Time

• Network conditions Throughput

• Reduce data sizes Quality, Compress

• Avoid redundant transfers Caching, Resumable

• Handle errors Timeout, Retry

Do it at better timeNetworking

Do It More Efficiently

Do it more efficiently

Quality of Service NSOperation and NSOperationQueue

Specify QoS classes on your work

• Specify the responsiveness and energy requirements of work.

• Classify long-running or resource-intensive operations in your existing code.

• Aim for >90% of time at Utility or below when the user is inactive.

Do it more efficientlyQuality of Service

Do It Less

Do it less

• Reduce CPU Use minimize timers• Performance Unit Test (Prince)

• Limit Screen Updates• Visual effects avoid placing over updates elements

• Minimize your I/O

Optimize and improve your resource use

Do it less

• Device will wake for notifications

• Set Push notification priority

Notifications

Summary

“Be a considerate background app”

Related

2013 Session 712 Energy Best Practices