pthread & thread support : issues?

After spending yesterday looking at the pcntl library, I did at one point attempt to get create_thread going, It didnt get very far, (it segfaulted on emalloc - perhaps because thread_init had not been called) but I did start wondering about the feasibilty.. Has anybody ever attempted it? The basic task of creating a set of php functions which wrapped the thread library - based perhaps on some of the code in python's thread library didnt seem particulary complex, however can anyone think of any issues that would occur? Would it only work as a built in module rather than a loadable module? anyway, I couldnt find any threads 'on threads:)' on php-dev discussing it - has anybody got any comments? regards alan