I didn't imply that the code remains and it's only data that is swapped out. The thread jumps to another complete address space. It's like a system call instr

I didn't imply that the code remains and it's only data that is swapped out. The thread jumps to another complete address space. It's like a system call instruction that instead of jumping into the kernel, jumps into another user process. There's a complete swap out of code and data in most cases. Just like with system calls how the kernel doesn't need a thread pool to respond to user requests applies here. The calling thread is just directly executing in the callee address space after the door_call(2). > Did you mean door_call or door_return instead of door_recv? I did not. I said there is no door_recv(2) systemcall. The 'server' doesn't wait for messages at all.