class Concurrent::AtomicFixnum

@!macro atomic_fixnum

A numeric value that can be updated atomically. Reads and writes to an atomic
fixnum and thread-safe and guaranteed to succeed. Reads and writes may block
briefly but no explicit locking is required.

@!macro thread_safe_variable_comparison

Performance:

```
Testing with ruby 2.1.2
Testing with Concurrent::MutexAtomicFixnum...
  3.130000   0.000000   3.130000 (  3.136505)
Testing with Concurrent::CAtomicFixnum...
  0.790000   0.000000   0.790000 (  0.785550)

Testing with jruby 1.9.3
Testing with Concurrent::MutexAtomicFixnum...
  5.460000   2.460000   7.920000 (  3.715000)
Testing with Concurrent::JavaAtomicFixnum...
  4.520000   0.030000   4.550000 (  1.187000)
```

@see http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/AtomicLong.html java.util.concurrent.atomic.AtomicLong

@!macro atomic_fixnum_public_api