QNX IPC mechanism is essentially cross-process function call, ie. message sender is always blocked while waiting for message reply and the server process cannot

QNX IPC mechanism is essentially cross-process function call, ie. message sender is always blocked while waiting for message reply and the server process cannot meaningfully combine waiting for message and some other event. Edit: in essence QNX messages work like syscalls, with the difference that there are multiple "systems" that accept "syscalls". For what it's worth Solaris has quite similar IPC mechanism that is mostly unused.