Question

I think I am not clear about when and how read/write blocks for various kind of files.
(disk file, pipe, socket, FIFO)

Could any one explain for both read and write scenarios of each file type?

Thanks!!

Answer 1

For a disk-based file, read and write may block briefly while the requested read/write is performed. A read at the end of a file will always return a short result, and a write to a file on a full FS will fail — barring various unusual circumstances, read/write to a plain file will never block indefinitely.

For pipes, sockets, and FIFOs, read will block if no data is available, and write will block if the pipe/socket/FIFO is “full” (e.g, you’ve written a bunch of data and the process on the other end hasn’t read it yet). The exact amount of data required to fill the buffer is variable; for a pipe, for instance, it’s typically between 4 and 64 kB.