The current killop implementation only tracks the op num of the most recently requested op to kill. This means that if I kill op 5 and then kill op 6 immediately afterward, and the execution of op 5 happens not to call checkForInterrupt() between the two killop requests, op 5 will not be killed.

It also appears there may be an issue if the op num of the last killed op is reused. It's possible that the op with the reused num will be killed immediately upon starting, though I haven't confirmed this with a test.