Behavior of Thread::new() on passed instances

The original implementation (see also #38) is designed so that Thread.new(a) makes a full copy of a in the newly created thread (unless mrb_type(a) == MRB_TT_DATA).
As a consequence, changes to a in any given thread are not visible to the other threads. This way, passing information between threads becomes a hard task.

Since I am still not sure about the reasons behind this choice, I have made an experimental branch in my own fork (pbosetti/mruby-thread) where the C macro MRB_THREAD_COPY_VALUES can be set to enable the original behavior (make copies) or leave undefined to switch to a "share the same instances" behavior.

The script examples/data.rb can be used to compare the two cases: when MRB_THREAD_COPY_VALUES is set, the changes to globals $data and $ary made in the subthread are not visible into the main thread. Conversely, if MRB_THREAD_COPY_VALUES, any change to instances passed to Thread::new() are visible to other threads.

The question is: can I make a PR for this?

Thanks,
Paolo

まず、#38で参照されている元の実装と、実験的なブランチ pbosetti/mruby-thread を読みます。examples/data.rbを使って2つのMRB_THREAD_COPY_VALUESの動作を比較し、共有インスタンスが受け入れられる設計なのか、またThread::newの意図された動作を定義するテストやドキュメントは何かを判断します。