5.4. Asynchronous Notification

Though the combination of blocking and nonblocking operations and the select method are sufficient for querying the device most of the time, some situations aren't efficiently managed by the techniques we've seen so far.

Let's imagine, for example, a process that executes a long computational loop at low priority, but needs to process incoming data as soon as possible. If the input channel is the keyboard, you are allowed to send a signal to the application (using the `INTR' character, usually CTRL-C), but this signaling ability is part of the tty abstraction, a software layer that isn't used for general char devices. What we need for asynchronous notification is something different. Furthermore, any input data should generate an interrupt, not just CTRL-C.