1. 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

2. 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

3. 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

4. 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

5. 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 */ };

6. 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

7. 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

8. 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

9. 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

10. 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