Signals and Threads - Advanced Unix Programming - Lecture Slides, Slides of Computer Programming

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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

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

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

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

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