This loop will hang the entire Buildslave process, including any other ongoing builds.  Use the Twisted reactor, and in particular `reactor.callLater`, to wait for events.  The Twisted process-handling code should react to the SIGCHLD that occurs when the process dies, so you really only need to wait the full `sigtermTime`, and then do nothing if either the process has already exited (according to Twisted) or `isDead`.