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(guile.info)Signals

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Signals
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Procedures to raise, handle and wait for signals.

 - primitive: kill pid sig
     Sends a signal to the specified process or group of processes.

     PID specifies the processes to which the signal is sent:

    PID greater than 0
          The process whose identifier is PID.

    PID equal to 0
          All processes in the current process group.

    PID less than -1
          The process group whose identifier is -PID

    PID equal to -1
          If the process is privileged, all processes except for some
          special system processes.  Otherwise, all processes with the
          current effective user ID.

     SIG should be specified using a variable corresponding to the Unix
     symbolic name, e.g.,

      - Variable: SIGHUP
          Hang-up signal.

      - Variable: SIGINT
          Interrupt signal.

 - primitive: raise sig
     Sends a specified signal SIG to the current process, where SIG is
     as described for the kill procedure.

 - primitive: sigaction signum [handler [flags]]
     Install or report the signal handler for a specified signal.

     SIGNUM is the signal number, which can be specified using the value
     of variables such as `SIGINT'.

     If ACTION is omitted, `sigaction' returns a pair: the CAR is the
     current signal hander, which will be either an integer with the
     value `SIG_DFL' (default action) or `SIG_IGN' (ignore), or the
     Scheme procedure which handles the signal, or `#f' if a non-Scheme
     procedure handles the signal.  The CDR contains the current
     `sigaction' flags for the handler.

     If ACTION is provided, it is installed as the new handler for
     SIGNUM.  ACTION can be a Scheme procedure taking one argument, or
     the value of `SIG_DFL' (default action) or `SIG_IGN' (ignore), or
     `#f' to restore whatever signal handler was installed before
     `sigaction' was first used.  Flags can optionally be specified for
     the new handler (`SA_RESTART' will always be added if it's
     available and the system is using restartable system calls.)  The
     return value is a pair with information about the old handler as
     described above.

     This interface does not provide access to the "signal blocking"
     facility.  Maybe this is not needed, since the thread support may
     provide solutions to the problem of consistent access to data
     structures.

 - primitive: restore-signals
     Return all signal handlers to the values they had before any call
     to `sigaction' was made.  The return value is unspecified.

 - primitive: alarm i
     Set a timer to raise a `SIGALRM' signal after the specified number
     of seconds (an integer).  It's advisable to install a signal
     handler for `SIGALRM' beforehand, since the default action is to
     terminate the process.

     The return value indicates the time remaining for the previous
     alarm, if any.  The new value replaces the previous alarm.  If
     there was no previous alarm, the return value is zero.

 - primitive: pause
     Pause the current process (thread?) until a signal arrives whose
     action is to either terminate the current process or invoke a
     handler procedure.  The return value is unspecified.

 - primitive: sleep i
     Wait for the given number of seconds (an integer) or until a signal
     arrives.  The return value is zero if the time elapses or the
     number of seconds remaining otherwise.

 - primitive: usleep i
     Sleep for I microseconds.  `usleep' is not available on all
     platforms.