Under  Linux,  opening a FIFO for read and write will suc?
       ceed both in blocking and non-blocking mode. POSIX  leaves
       this  behaviour undefined. This can be used to open a FIFO
       for writing while there are no readers available.  A  pro?
       cess  that  uses  both  ends of the connection in order to
       communicate with itself should be very  careful  to  avoid
       deadlocks.