Advanced UNIX programming

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
• Presentations next week
• Demo next week
• Quiz Monday
• Mondays and todays lecture material
• Mondays lecture material included in finals

3
Week 14 Topics

• Signals and threads
• Terminal 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)
• 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
• struct termios
• 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_ccNCCS / control characters
  /

6
Functions to get and set the fields in the
termios structure

• include lttermios.hgt
• 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_ccVMIN ???, c_ccVTIME ???
• VMIN gt 0, VTIME gt 0
• VMIN 0, VTIME gt 0
• VMIN gt 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
• 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
• 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