If I run this code, which should just be a loop which
creates-then-joins a thread (looping twice), I get a crash at the end:

     set I16, 0
again:
     inc I16
     new P5, .ParrotThread
     find_global P6, "_foo"
     find_method P0, P5, "thread3"
     invoke
     set I5, P5
     getinterp P2
     find_method P0, P2, "join"
     invoke
     lt I16, 2, again
     print "done\n"
     end

.pcc_sub _foo:
     invoke P1

The problem is that when joining the _second_ time, in pt_thread_join()
you get a return value from joining the thread--which happens to
contain a thread-interpreter PMC:

(gdb) p (char*)((PMC*)retval)->vtable->isa_str->strstart
$2 = 0x1dc40c "ParrotThread ParrotInterpreter"

This then gets cloned, which ultimately ends up messing up the
interpreter_array[] (things end up in the wrong slot), and
pt_join_threads() ends up trying to join a bogus thread, and you get a
crash.

So, the bug seems to be that the second time through, you get a return
value from the thread. I don't know why this is happening--haven't
tried digging yet.

JEff