How to Prevent Timer Slowing Down in Background

How to prevent Timer slowing down in background

This is because of the App Nap. You can disable App Nap but it is not recommended.

var activity: NSObjectProtocol?
activity = ProcessInfo().beginActivity(options: .userInitiatedAllowingIdleSystemSleep, reason: "Timer delay")

The default tolerance value of timer is zero but The system reserves the right to apply a small amount of tolerance to certain timers regardless of the value of tolerance property.

Prevent NSTimer firing delays in background app

This is App Nap. The display app can do the following to avoid napping:

id activity = [[NSProcessInfo processInfo] beginActivityWithOptions:NSActivityUserInitiatedAllowingIdleSystemSleep reason:@"whatever"];

When it can allow napping again, you should do:

[[NSProcessInfo processInfo] endActivity:activity];

OS X Cocoa timer not fired when application on background

Use beginActivityWithOptions:reason: to disable app nap for your application.

Chrome: timeouts/interval suspended in background tabs?

I recently asked about this and it is behaviour by design. When a tab is inactive, only at a maximum of once per second the function is called. Here is the code change.

Perhaps this will help:
How can I make setInterval also work when a tab is inactive in Chrome?

TL;DR: use Web Workers.

Why timer invoke its block so quickly sometimes

To understand the behavior, you need to understand how NSTimer and RunLoop works. In simple terms, a RunLoop would check if the Timer should fire, if yes it would notify the Timer to fire the selector, else it won't. Now, since you are on the background, your RunLoop is not checking for events so it won't be able to notify the Timer. But once it goes to foreground, it would see that it would need to notify the Timer even if it passed the fireDate.

TimeLine Diagram:

Let A(5th second) and B(10th second) be timer fire events. Scheduled on a timer Timer.scheduledTimer(withTimeInterval: 5.0, repeats: true)

C is entered background (0 seconds)

D be coming back to foreground (9th second, between A and B).

-----> A ------> B

C--------->D

Explanation:

On C, the RunLoop would be paused. Therefore Event A is not able to be processed until the RunLoop has resumed processing, which is on Event D. Upon Event D, it will see that Event A should fire so it would notify the Timer. After a second, the RunLoop would see that Event B has happened so it would notify the Timer again. This scenario explains why your events are printing in a second's interval. It is just the delayed event handling that makes it seem that it fired earlier, when in reality it was processed late.

Apple Doc:

A timer is not a real-time mechanism. If a timer’s firing time occurs
during a long run loop callout or while the run loop is in a mode that
isn't monitoring the timer, the timer doesn't fire until the next time
the run loop checks the timer. Therefore, the actual time at which a
timer fires can be significantly later.

resources: What is an NSTimer's behavior when the app is backgrounded?, NSRunLoop and Timer Docs

Suggestions:

Stop your timer once app goes background, but store the fireDate. Once coming back to foreground, check if fireDate is past Date(). Then create a new Timer to handle events while on foreground.

JavaScript setTimeout() slows down under heavy load

Here is an article from Google where the author discusses their work on timers for Gmail. They found that having a single high-frequency timer was faster than using multiple timers if they had heavy and rapid timer use.

You could have one timer that fires every 5ms, and add all of your elements that need to be faded to a data structure that tracks where they are in the fading process. Then your one timer can look through that list and perform the next fade for each element each time it is triggered.

On the other hand, have you tried using a library like Mootools or JQuery rather than rolling your own animation framework? Their developers have put a lot of work into optimizing these kinds of operations.

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