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REF TIMES                                           John Gibson Apr 1994

        COPYRIGHT University of Sussex 1994. All Rights Reserved.

<<<<<<<<<<<<<<<<<<<<<                             >>>>>>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<<<<<       DATE TIME AND         >>>>>>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<<<<<      TIMER PROCEDURES       >>>>>>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<<<<<                             >>>>>>>>>>>>>>>>>>>>>>

This REF file describes  all the procedures in  Poplog for dealing  with
times and dates, CPU times, and timing.

         CONTENTS - (Use <ENTER> g to access required sections)

  1   Date and Time Procedures

  2   CPU Time

  3   Timer Procedures

1  Date and Time Procedures

sys_real_time() -> time                                      [procedure]
        Returns the  time as  an integral  number of  seconds since  the
        standard Unix base date, i.e. 00:00 GMT on 1 Jan 1970 (N.B. this
        value is a biginteger, not a simple integer).

sys_convert_date(time, local) -> string                      [procedure]
        Given a time in seconds since 00:00 GMT 1 Jan 1970 (as  returned
        by sys_real_time, or a file date returned by sys_file_stat etc),
        returns a date string in  the standard operating system  format,

            'nnn mmm dd hh:mm:ss timezone yyyy'

        in Unix systems (where nnn is the day name), and

            'dd-mmm-yyyy hh:mm:ss'

        in VMS systems.

        In VMS systems, the local  argument is ignored; in Unix  systems
        it specifies whether time is interpreted as local time (true) or
        GMT (false), and  therefore affects  the value  of the  timezone
        substring (which depends upon the timezone C library  function -
        see ctime(3) in the Unix Programmers Manual.)

sysdaytime() -> string                                       [procedure]
        Returns the current date  and time as a  string in the  standard
        operating system form. E.g, in Unix:

            sysdaytime() =>
            ** Mon Mar  6 12:43:15 GMT 1995

        This procedure is the same as

            sys_convert_date(sys_real_time(), true)

2  CPU Time

systime() -> hsecs                                           [procedure]
        Returns the elapsed CPU time for this run of the Poplog  system,
        an integer number of hundredths of a second.

        The returned value  refers to  the amount of  time spent  within
        Poplog. It does not refer to "real" time and is not effected  by
        any other processes running on your machine

timediff() -> float_secs                                     [procedure]
        Returns the elapsed CPU time since the last call of timediff, as
        a floating-point number of seconds SECS (the first call produces
        a meaningless  result).  This  procedure uses  systime,  so  the
        resolution of the result will be hundredths of a second.

        The returned value  refers to  the amount of  time spent  within
        Poplog. It does not refer to "real" time and is not effected  by
        any other processes running on your machine

3  Timer Procedures

The variables pop_timeout  and pop_timeout_secs are  also available  for
timing-out terminal read operations -- see REF * SYSIO for details.

For a general  discussion of asynchronous  trap procedures and  signals,
see REF * ASYNC.

sys_timer(ast_p, flags) -> usecs_or_false                    [procedure]
sys_timer(ast_p)        -> usecs_or_false
usecs_or_false -> sys_timer(ast_p, flags)
usecs_or_false -> sys_timer(ast_p)
        This  procedure  and  its  updater  provide  multiple  real   or
        `virtual'  interval  timers,  each  attached  to  a   particular
        asynchronous trap procedure ast_p that  gets run when the  timer

        (See  Asynchronous  Trap  Procedures  in  REF * ASYNC  for  full
        details of the ast_p  argument, which may also  be a pair  whose
        front  is  the  procedure.   Note  that  different  timers   are
        discriminated by == applied to the ast_p structure given;  hence
        if a pair is supplied, the timer is attached to the pair, not to
        the procedure.  If you  supply the  ASTP_ERROR_DELETE flag  with
        ast_p, the timer is cancelled by a mishap or setpop.)

        The updater sets a timer going for usecs microseconds which will
        execute ast_p  when  it  expires  (asynchronously,  i.e.  inside
        whatever procedures  the  system is  currently  executing).  Any
        current timer running for ast_p  is first cancelled. Unless  the
        TIMER_REPEAT bit is set in  the flags argument (see below),  the
        timer setting is  one-shot, i.e.  is not reset  when it  expires
        (ast_p can set another timer for itself if required).

        usecs may  be  a  biginteger, the  largest  time  allowed  being
        pop_max_int seconds plus 999999  microseconds (i.e. the  seconds
        part of usecs must be within the range of a simple integer). The
        smallest time allowed is 0, but assigning a non-zero time  value
        smaller than the resolution of the system clock sets a timer for
        that resolution (e.g. 1/100th second on VAXen and Sun-4 systems,
        1/50th sec on MC68000  systems, etc). A  zero time value  causes
        the timer to expire immediately.

        Assigning false instead of usecs  cancels any current timer  for

        The base  procedure returns  the  number of  microseconds  usecs
        remaining on  the timer  for  ast_p, or  false  if no  timer  is
        running for it.

        The optional flags  argument is  an integer  whose bits  control
        various aspects of the timer; symbolic names for these bits  are
        defined in INCLUDE * AST. Currently, they are:

                    (Updater only, ignored  by base  procedure) If  set,
                    then  the  timer  runs  in  process  "virtual"  time
                    instead of real  time, i.e. it  runs only while  the
                    Poplog process  is executing  code, and  not  during
                    wait states or when swapped  out (or in Unix,  while
                    operating system calls are being executed).

                    (Base only, ignored by updater) If set, then getting
                    the time remaining  on a  timer will  simultaneously
                    cancel it.

                    (Updater only, ignored  by base  procedure) If  set,
                    then  instead  of  being  one-shot  the  timer  will
                    continue to  repeat every  usecs microseconds  until
                    cancelled. (I.e, if the current  time is T then  the
                    timer is set  to fire at  times T+usecs,  T+2*usecs,
                    T+3*usecs, ... etc.)

                    (N.B. Using this flag  is generally not  appropriate
                    for a  virtual  timer,  since this  will  cause  the
                    execution time of the handler itself to be  included
                    in the interval usecs, i.e.  the next timer will  be
                    running  during  the  execution  of  ast_p  for  the
                    previous one. A virtual timer should therefore reset
                    itself at the end; this (in effect) stops the  timer
                    while the handler is running.)

        If the flags argument is omitted, all bits default to 0.

        For example,  to  set a  5-second  (real) timer  which  prints a
        message and resets itself:

            define timer_trap();
                "hello" =>
                5e6 -> sys_timer(timer_trap)    ;;; 1e6 = 1 sec in usec

            5e6 -> sys_timer(timer_trap);       ;;; start it off
            ** hello
            ** hello

        Note that currently, space is allowed for upto 32 timers running
        together at any one time.

syssleep(hsecs)                                              [procedure]
        Waits (with  syshibernate) until  hsecs hundredths  of a  second
        have elapsed (for which it uses a real timer set by sys_timer).

syshibernate()                                               [procedure]
        Suspends the  current  Poplog  process  awaiting  some  form  of
        interrupt caused by an asynchronous trap or signal firing  (e.g.
        a timer trap set by sys_timer, a SIG_INT caused by Ctrl-C  typed
        on the terminal, or (when X is running) an X event, etc).

        After the interrupting event  has been processed (and  providing
        it does not cause  an abnormal exit),  the call of  syshibernate

        The usual way for a program  to wait for a particular  condition
        of interest, processing asynchronous events in the meantime,  is

            until condition do syshibernate() enduntil;

--- C.all/ref/times
--- Copyright University of Sussex 1994. All rights reserved.