TIP #364: Threading Support: Configuration and Package
在 [incr Tcl] , TDBC 之後，Thread package 也成為內建的 contributed package，因此 Thread package 也會成為 8.6 的一員。
This will have no effect on Windows and OSX, where threaded configurations are default anyway, but will have an impact on other Unixes (Linux, Solaris, etc.)
The main issues arising from this relate to the Expect and TclX packages. This is because they make fork and signal commands available; these APIs are troublesome because of how they interact with Tcl's notifier and the POSIX Thread system in general.