The pertinent text I missed was actually out of "threads" which was:
Correspondingly, sending a signal to a thread does not disrupt the operation the thread is currently working on: The signal will be acted upon after the current operation has completed. For instance, if the thread is stuck on an I/O call, sending it a signal will not cause the I/O call to be interrupted such that the signal is acted up immediately.
Nothing in the documentation suggests that signals are not the way to perform IPC, but simply threads don't react to signals as well as processes. Keep in mind, I don't want to simply suspend or terminate the thread, but interrupt it and send it off in another direction. So, the problem restated is, I guess, how do I interrupt a thread from an I/O operation?