For optimal energy efficiency, classify dispatch queues for prioritization by the system. Also see Synchronization in Threading Programming Guide. Listing 5-2Not recommended: Using an energy-inefficient timer as a synchronization toolįor more information about using dispatch queues and other synchronization features of Grand Central Dispatch, see Concurrency Programming Guide and Grand Central Dispatch (GCD) Reference.
Until the work in the first thread is completed, the usleep timer in the second thread continually wakes the system only to determine whether the work in the first thread has completed.
#SWIFT IOS IDLE TIMER CODE#
The code in Listing 5-2 performs work on one thread while another thread and a completion handler use a timer to periodically check whether work on the first thread has completed. Grand Central Dispatch (GCD) provides dispatch queues, dispatch semaphores, and other synchronization features that are more efficient than timers. Use GCD Tools for Synchronization Instead of Timers Local and Remote Notification Programming GuideĭNS Service Discovery Programming Guide and NSNetServices and CFNetServices Programming Guide Updates to systemwide files or directoriesĬreate an event stream with the File System Events API. Table 5-1Obtaining event notifications for system servicesĪpproach to follow for obtaining event notificationsĭispatch Sources in Concurrency Programming Guide Listing 5-1Recommended: Use an energy-efficient dispatch source to obtain file change notifications Instead of using timers to watch for events, use a more efficient service, such as a dispatch source. Timers prevent the CPU from going to or staying in the idle state, which increases energy usage and consumes battery power. Some apps use timers to monitor for changes to file contents, network availability, and other state changes. Get Event Notifications Without Using Timers Regardless of the scenario, if there are many timer-invoked wakeups, the energy impact is high. Some timers are executed without suitable timeouts, causing them to continue firing when they’re no longer needed. Other apps use timers as synchronization tools when they should use semaphores or other locks to achieve the greatest efficiency. For example, some apps use timers to poll for state changes when they should respond to events instead.
If you use timers in your app, consider whether you truly need them. If a timer causes the system to wake, it incurs that cost.Īpps often use timers unnecessarily. Waking the system from an idle state incurs an energy cost when the CPU and other systems are awakened from their low-power, idle states. A timer waits until a certain interval has elapsed and then fires, performing a specific action such as sending a message to its target object. If you must use timers, employ them efficiently.Ī timer lets you schedule a delayed or periodic action. The NSURLSession API, for example, provides the ability to perform out-of-process background URL sessions and receive notifications when they are complete. You can reduce your app’s energy usage by implementing energy-efficient APIs instead of timers.
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