Crash when using [NSTimer fire]

FROM : Gwynne
DATE : Fri Nov 19 18:19:22 2004

I'm experiencing a confusing crash when using NSTimer's -fire method to
force a timer to fire before its fire date. This happens when using a
timer with a very large interval (close order of 5 years), which I do
in order to avoid having to separate two extremely similar code paths
from each other. I started out with a non-repeating timer, but it would
somehow get invalidated immediately and therefore -fire didn't work. I
switched to a repeating timer (which didn't matter, since the timer's
selector invalidates and removes the timer anyway), and ended up with a
crash inside objc_msgSend() called from [NSCFTimer fire]. I traced it
down at the assembly level, and it seems that the instance of NSTimer
is getting mangled so when it calls -timeInterval on itself, there's an
invalid object there. I could only get the crash to occur without
assembly-level debugging, but there's nothing in my secondary threads
that goes anywhere NEAR that timer. I ran with libguardmalloc, and
nothing's tromping any memory. When I switched to calling the timer's
target/selector directly, the crash vanished and exhaustive testing
with both single-processor and multi-processor has revealed no issues
whatsoever. Is there any known issue with large timer intervals and
[NSTimer fire]?

-- Gwynne, key to the Code that runs us all
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