ReadWriteLock donated by @alexdowad

[jdantonio]

Merges ReadWriteLock donated by @alexdowad in #146.

• Copied the source file to the lib/concurrent/atomic directory
• Moved the class under the Concurrent namespace
• Moved the stress tests to examples/benchmark_read_write_lock.rb
• Updated the stress tests to use OptionsParser
• Created a spec file

To-do

• Yardoc
• Tests
• Refactor
• Changelog
• Readme

[alexdowad]

@jdantonio, thank you very much for cleaning up my code!

[jdantonio]

@alexdowad No clean up was necessary. Your code is awesome! All I had to do was integrate it into the project. Thank you very much for donating it!

[pitr-ch]

better to wrap release_read_lock in ensure block, to prevent leaving it locked

[jdantonio]

My next commit will have an ensure block that releases the lock but is also sensitive to errors raised before the lock is acquired (such as when the maximum number of readers/writers is reached).

[pitr-ch]

right, it has to be:

def with_read_lock
  acquire_read_lock
  begin
    yield
  ensure
    release_read_lock
  end
end

not just ensure at the end, good catch

[pitr-ch]

@alexdowad Thanks for the code!

[pitr-ch]

The complex conditions could be extracted to methods to improve readability. E.g.

def readers(c = @count.value)
  c & MAX_READERS
end

def waiting_writer?(c = @counter.value)
  c >= WAITING_WRITER
end

# etc

[jdantonio]

I believe this PR is ready to merge. It has nearly 100% code coverage, full yardoc, better exception handling, a few readability updates (methods for some of the bitwise operations used in conditionals), and the stress tests still pass with comparable performance.