I have a library that potentially creates and invalidates/destroys a
lot of NSTimers. Basically, users request operations to be completed
and they pass an optional timeout. If the operation completes in the
appropriate time, the timer is invalidated. Otherwise the timer
fires, and the operation is cancelled. Operations are queued, and
only one operation is executed at a time.
So I was wondering if it would be better to create a single repeating
NSTimer, and simply change its fireDate. The documentation for
CFRunLoopTimerSetNextFireDate seems to indicate as much:
Resetting a timer’s next firing time is a relatively expensive
operation and should not be done if it can be avoided; letting timers
autorepeat is more efficient. In some cases, however, manually-
adjusted, repeating timers are useful. For example, if you have an
action that will be performed multiple times in the future, but at
irregular time intervals, it would be very expensive to create, add to
run loop modes, and then destroy a timer for each firing event.
Instead, you can create a repeating timer with an initial firing time
in the distant future (or the initial firing time) and a very large
repeat interval—on the order of decades or more—and add it to all the
necessary run loop modes. Then, when you know when the timer should
fire next, you reset the firing time with
CFRunLoopTimerSetNextFireDate, perhaps from the timer’s own callback
function. This technique effectively produces a reusable, asynchronous
timer.
However I'm not sure how safe it is to use the setFireDate method of
NSTimer. Consider the following code:
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.2
target:self
selector:@selector(timeout:)
userInfo:nil
repeats:NO];
[NSThread sleepForTimeInterval:2.0];
// This line will properly prevent the timer from firing
//[timer invalidate];
// This line will NOT
[timer setFireDate:[NSDate distantFuture]];
Why is this exactly?_______________________________________________
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