How to create a timer in background thread in iOS

Question

I need to create two timers. One is on the UI thread, the other one is on the background thread. These timers are independent from each other.

Scenario that I will be using; I basically need this to test the responsiveness of UI thread. TImer in uI thread updates lastUpdatedDatetime property every 200ms in UI thread. There is also a background thread that polls this lastupdatedDatetime property every 200ms.

Does anyone know how can I achieve this?

I think your question is similar to this one: http://stackoverflow.com/questions/8304702/how-do-i-create-a-nstimer-on-a-background-thread — Selkie, Jul 16 '12 at 22:36

score 1 · Answer 1 · answered Jul 16 '12 at 22:47

The point of NSTimer is to be able to schedule things to be run on a thread (usually the main thread) while it is handling other events on a run loop. If all you want to do on the background thread is to poll something every 200 ms, then it is far easier to not use an NSTimer and to instead just sleep the background thread. So setup an NSTimer as usual on your main thread and on the background thread do something like:

while (stillRunning) {
    usleep(200*1000);
    // Do something with lastUpdatedDatetime
}

This technique is wasteful of a thread but is probably more deterministic for testing purposes than using Grand Central Dispatch.

Keep in mind if lastUpdatedDatetime is an NSDate that it should be set as an atomic property so that when you access it on the background thread you are sure to receive a valid object.

score 0 · Accepted Answer · answered Jul 16 '12 at 22:39

look into dispatch_async and dispatch_after

dispatch_async will let you fire off a call to another thread, this is what I use to do main thread changes.

dispatch_after will let you delay a dispatch_async for a number of seconds.

These two in conjunction will let you go back and forth between threads.

here is the documents on Grand Central Dispatch

How to create a timer in background thread in iOS

2 Answers2