Thread-safe time-limited cache for Ruby

 SynCache stores cached objects in a Hash that is protected by an advanced
 two-level locking mechanism which ensures that:
 .
  * Multiple threads can add and fetch objects in parallel.
  * While one thread is working on a cache entry, other threads can access
    the rest of the cache with no waiting on the global lock, no race
    conditions nor deadlock or livelock situations.
  * While one thread is performing a long and resource-intensive
    operation, other threads that request the same data will be put on hold,
    and as soon as the first thread completes the operation, the result will be
    returned to all threads.
 .
 This package provides SynCache module for Ruby and a DRb server that exports a
 SynCache::Cache object for use in Ruby programs.