>Doors at the end of the day are a control transfer primitive. In a very real sense the calling thread is simply transferred to the callee's address space and c

>Doors at the end of the day are a control transfer primitive. In a very real sense the calling thread is simply transferred to the callee's address space and continues execution there until a door_return(2) syscall transfers it back into the caller address_space. Your phrasing is misleading. A door is a scheduler operation. What would it even mean for a thread to go from a caller to a callee? They are different processes with completely different contexts on the system. Different owners, different address spaces, etc. What the door is doing is passing time on a CPU core from the calling thread to the receiving thread and back.