Here’s a stupid little hack that just crossed my mind.
If you ever needed keep a counter which you incremented by 1 from multiple threads and you wanted to save yourself from having to wrap the increment in a Mutex because you were super anal about speed and you are using MRI (not jruby or rubinius)… then instead of:
@counter = 0
...
@mutex.synchronize { @counter += 1 }
you could do:
@counter = '0' ... @counter.succ! ... @counter.to_i
Since String#succ! is just a C function it’ll be thread safe. But that’s probably only guaranteed in MRI. Any other VM could have an implementation of succ! which is pre-emptable.
In my benchmarks its about 20x faster.
The C-implementation for String#succ! is:
rb_str_shared_replace(str, rb_str_succ(str));
That doesn’t look thread-safe to me. :)
Comment by Per Velschow — December 6, 2008 @ 12:21 am
It’s thread safe because MRI uses green threads and therefore won’t switch threads in the middle of a native C function.
Like I said in other VMs all bets are off.
Comment by coderrr — December 6, 2008 @ 7:35 am