Hi,

In message "[ruby-talk:10716] Re: Threading model change, proposal"
    on 01/02/12, "Alex Maranda" <alex_maranda / telus.net> writes:

|1) "green" threads [Ruby as of today]
|2) system threads, with a non-reentrant interpreter [Python, global
|interpreter lock]
|3) system threads, fully reentrant interpreter [no example comes to mind]
|
|The reason Python stopped at 2) is because 3) is hard. The reason Ruby
|stopped at 1) is because ...LOL.

Two good reasons, one bad reason:

  * universal availability, even on DOS machines
  * universal behavior
  * conservative GC does not run fine with native threads without
    affecting portability

							matz.