(libc.info.gz) Interrupt Input

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 13.16 Interrupt-Driven Input
 ============================
 
 If you set the `O_ASYNC' status flag on a file descriptor ( File
 Status Flags), a `SIGIO' signal is sent whenever input or output
 becomes possible on that file descriptor.  The process or process group
 to receive the signal can be selected by using the `F_SETOWN' command
 to the `fcntl' function.  If the file descriptor is a socket, this also
 selects the recipient of `SIGURG' signals that are delivered when
 out-of-band data arrives on that socket; see  Out-of-Band Data.
 (`SIGURG' is sent in any situation where `select' would report the
 socket as having an "exceptional condition".   Waiting for I/O.)
 
    If the file descriptor corresponds to a terminal device, then `SIGIO'
 signals are sent to the foreground process group of the terminal.
  Job Control.
 
    The symbols in this section are defined in the header file `fcntl.h'.
 
  -- Macro: int F_GETOWN
      This macro is used as the COMMAND argument to `fcntl', to specify
      that it should get information about the process or process group
      to which `SIGIO' signals are sent.  (For a terminal, this is
      actually the foreground process group ID, which you can get using
      `tcgetpgrp'; see  Terminal Access Functions.)
 
      The return value is interpreted as a process ID; if negative, its
      absolute value is the process group ID.
 
      The following `errno' error condition is defined for this command:
 
     `EBADF'
           The FILEDES argument is invalid.
 
  -- Macro: int F_SETOWN
      This macro is used as the COMMAND argument to `fcntl', to specify
      that it should set the process or process group to which `SIGIO'
      signals are sent.  This command requires a third argument of type
      `pid_t' to be passed to `fcntl', so that the form of the call is:
 
           fcntl (FILEDES, F_SETOWN, PID)
 
      The PID argument should be a process ID.  You can also pass a
      negative number whose absolute value is a process group ID.
 
      The return value from `fcntl' with this command is -1 in case of
      error and some other value if successful.  The following `errno'
      error conditions are defined for this command:
 
     `EBADF'
           The FILEDES argument is invalid.
 
     `ESRCH'
           There is no process or process group corresponding to PID.
 

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