text: //
  //  MSWeakTimer.h
  //  MindSnacks
  //
  //  Created by Javier Soto on 1/23/13.
  //
  //
  
  #import <Foundation/Foundation.h>
  
  /**
   `MSWeakTimer` behaves similar to an `NSTimer` but doesn't retain the target.
   This timer is implemented using GCD, so you can schedule and unschedule it on arbitrary queues (unlike regular NSTimers!)
   */
  @interface MSWeakTimer : NSObject
  
  /**
   * Creates a timer with the specified parameters and waits for a call to `-schedule` to start ticking.
   * @note It's safe to retain the returned timer by the object that is also the target.
   * or the provided `dispatchQueue`.
   * @param timeInterval how frequently `selector` will be invoked on `target`. If the timer doens't repeat, it will only be invoked once, approximately `timeInterval` seconds from the time you call this method.
   * @param repeats if `YES`, `selector` will be invoked on `target` until the `MSWeakTimer` object is deallocated or until you call `invalidate`. If `NO`, it will only be invoked once.
   * @param dispatchQueue the queue where the delegate method will be dispatched. It can be either a serial or concurrent queue.
   * @see `invalidate`.
   */
  - (id)initWithTimeInterval:(NSTimeInterval)timeInterval
                      target:(id)target
                    selector:(SEL)selector
                    userInfo:(id)userInfo
                     repeats:(BOOL)repeats
               dispatchQueue:(dispatch_queue_t)dispatchQueue;
  
  /**
   * Creates an `MSWeakTimer` object and schedules it to start ticking inmediately.
   */
  + (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)timeInterval
                                          target:(id)target
                                        selector:(SEL)selector
                                        userInfo:(id)userInfo
                                         repeats:(BOOL)repeats
                                   dispatchQueue:(dispatch_queue_t)dispatchQueue;
  
  /**
   * Starts the timer if it hadn't been schedule yet.
   * @warning calling this method on an already scheduled timer results in undefined behavior.
   */
  - (void)schedule;
  
  /**
   * Sets the amount of time after the scheduled fire date that the timer may fire to the given interval.
   * @discussion Setting a tolerance for a timer allows it to fire later than the scheduled fire date, improving the ability of the system to optimize for increased power savings and responsiveness. The timer may fire at any time between its scheduled fire date and the scheduled fire date plus the tolerance. The timer will not fire before the scheduled fire date. For repeating timers, the next fire date is calculated from the original fire date regardless of tolerance applied at individual fire times, to avoid drift. The default value is zero, which means no additional tolerance is applied. The system reserves the right to apply a small amount of tolerance to certain timers regardless of the value of this property.
   As the user of the timer, you will have the best idea of what an appropriate tolerance for a timer may be. A general rule of thumb, though, is to set the tolerance to at least 10% of the interval, for a repeating timer. Even a small amount of tolerance will have a significant positive impact on the power usage of your application. The system may put a maximum value of the tolerance.
   */
  @property (atomic, assign) NSTimeInterval tolerance;
  
  /**
   * Causes the timer to be fired synchronously manually on the queue from which you call this method.
   * You can use this method to fire a repeating timer without interrupting its regular firing schedule.
   * If the timer is non-repeating, it is automatically invalidated after firing, even if its scheduled fire date has not arrived.
   */
  - (void)fire;
  
  /**
   * You can call this method on repeatable timers in order to stop it from running and trying
   * to call the delegate method.
   * @note `MSWeakTimer` won't invoke the `selector` on `target` again after calling this method.
   * You can call this method from any queue, it doesn't have to be the queue from where you scheduled it.
   * Since it doesn't retain the delegate, unlike a regular `NSTimer`, your `dealloc` method will actually be called
   * and it's easier to place the `invalidate` call there, instead of figuring out a safe place to do it.
   */
  - (void)invalidate;
  
  - (id)userInfo;
  
  @end