Concurrent::Hash and Concurrent::Array are not fully threadsafe on CRuby

Concurrent::Hash and Concurrent::Array are not fully threadsafe on CRuby.

This can be demonstrated for Array with:

require 'concurrent/array'

array = Concurrent::Array.new
array << 0

20.times.map do |i|
  Thread.new { array.map!{|v| sleep 0.001; v + 1} }
end.each(&:join)
p array

This returns [1].

For Hash this code shows the issue:

require 'concurrent/hash'

hash = Concurrent::Hash.new
hash[:a] = 0

20.times.map do |i|
  Thread.new { hash.transform_values!{|v| sleep 0.001; v + 1} }
end.each(&:join)
p hash

This returns {a: 1}.

In both cases we would expect to see 20 instead of 1.

* Ruby implementation:             Ruby
* `concurrent-ruby` version:       1.1.9
* `concurrent-ruby-ext` installed: no
* `concurrent-ruby-edge` used:     no