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cmacossocketsoperating-systemkqueue

Kqueue on regular files

Is kqueue (on OS X) useful for reading/writing regular files? I know that epoll is not useful for regular files on Linux, so I'm wondering if the same is true for kqueue.

EDIT: I don't mean reading/writing files, obviously read() and write() are for that. I meant, "is kqueue actually useful for detecting when a file is readable/writable?"

Solution

  • Yes, kqueue can be used to watch files for readability. From the man page:

     EVFILT_READ      Takes a file descriptor as the identifier, and returns
                  whenever there is data available to read.  The behavior
                  of the filter is slightly different depending on the
                  descriptor type.

 [...]

                  Vnodes
                      Returns when the file pointer is not at the end of
                      file.  data contains the offset from current posi-
                      tion to end of file, and may be negative.

    ("vnodes", in this context, are regular files.)

    As regular files are always writable, it makes no sense to apply EVFILT_WRITE to them.