MSWeakTimer

Description

Thread-safe NSTimer alternative that doesn't retain the target and supports being used with GCD queues.

Motivation

The first motivation for this class was to have a type of timer that objects could own and retain, without this creating a retain cycle ( like NSTimer causes, since it retains its target ). This way you can just release the timer in the -dealloc method of the object class that owns the timer.

The other problem when using NSTimer is this note on the documentation:

Special Considerations

You must send this message from the thread on which the timer was installed. If you send this message from another thread, the input source associated with the timer may not be removed from its run loop, which could prevent the thread from exiting properly.

More often than not, an object needs to create a timer and invalidate it when a certain event occurs. However, doing this when that object works with a private GCD queue gets tricky. This timer object is thread safe and doesn't have the notion of run loop, so it can be used with GCD queues and installed / invalidated from any thread or queue.

Related Stackoverflow question.

How to Use

Create an MSWeakTimer object with this class method:

+ (MSWeakTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)timeInterval
                                         target:(id)target
                                       selector:(SEL)selector
                                       userInfo:(id)userInfo
                                        repeats:(BOOL)repeats
                                  dispatchQueue:(dispatch_queue_t)dispatchQueue;

Check out the code in the sample app.

Compatibility

• Supports ARC. If you want to use it in a project without ARC, mark MSWeakTimer.m with the linker flag -fobjc-arc.
• Should work with iOS4+ and Mac OSX 10.6+.