Advanced UNIX programming Fall 2002 Instructor: Ashok Srinivasan Lecture 37 Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

Announcements Project Quiz Monday Presentations next week Demo next week Quiz Monday Monday’s and today’s lecture material Monday’s lecture material included in finals

Week 14 Topics Signals and threads Terminal I/O Signal driven I/O APUE chapter 11 Signal driven I/O UNP chapter 22 Non-blocking I/O UNP chapter 15

Terminal I/O Canonical mode (not our focus) Non-canonical mode The default mode, input line by line Non-canonical mode Input characters are not assembled termios structure tcgetattr and tcsetattr Turning on the non-canonical mode

termios structure struct termios Stores all the characteristics of a terminal device that we can examine and change termios.h { tcflag_t c_iflag; /* input flag */ tcflag_t c_oflag; /* output flag */ tcflag_t c_cflag; /* control flags */ tcflag_t c_lflag; /* local flags */ cc_t c_cc[NCCS]; /* control characters */ };

Functions to get and set the fields in the termios structure #include <termios.h> int tcgetattr(int fildes, struct termios *termios_p) int tcsetattr(int fildes, int optional_actions, const struct termios *termios_p) optional_actions TCSANOW TCSADRAIN TCSAFLUSH

Turn on the noncanonical mode Unset the ICANON flag in c_lflag myterm.c_lflag & = ~ICANON When will a read return using the noncanonical mode for input? Number of characters (VMIN) Time (VTIME) Specified in the c_cc field c_cc[VMIN] = ???, c_cc[VTIME] = ??? VMIN > 0, VTIME > 0 VMIN = 0, VTIME > 0 VMIN > 0, VTIME = 0 VMIN = 0, VTIME = 0 See example1.c and example2.c

Signal driven I/O The kernel raises a signal when something happens to a file descriptor Signal driven I/O for sockets Establish a signal handler for SIGIO Set the socket owner Enable signal-driven I/O for the socket

When is SIGIO raised? For UDP sockets For TCP sockets A datagram arrives An error occurs For TCP sockets A connection request has completed A disconnect request has been initiated A disconnect request has completed Half of a connection has been shut down Data has arrived Data has been sent Too many SIGIOs for a TCP socket – rarely used

Non-blocking I/O For input operations For output operations For accept read, recv, recvfrom, etc. If the operation cannot be satisfied, return with an error of EWOULDBLOCK For output operations write send, sendto, etc. If no buffer space, return with an error of WOULDBLOCK For accept If a new connection is not available, return with an error of EWOULDBLOCK For connect If the connection cannot be established right away, EINPROGRESS is returned