HELP ITIMER_VIRTUAL                              John Williams, Feb 1990

-- Introduction --------------------------------------------------------

LIB * ITIMER_VIRTUAL defines a POP11 interface to the virtual interval
timer (ITIMER_VIRTUAL) provided by the C library function SETITIMER(2).

The ITIMER_VIRTUAL timer runs in process virtual time (sometimes known
as "cpu time"). It runs only when Poplog is executing. A SIGVTALRM
signal is delivered when it expires.

The interface to ITIMER_VIRTUAL is modelled on the interface to the
real-time timer (ITIMER_REAL). It defines the following identifiers:

    syssetvtimer            (analogous to *SYSSETTIMER)
    syscanvtimer            (analogous to *SYSCANTIMER)
    vtimer_interrupt        (analogous to *TIMER_INTERRUPT)


PLEASE NOTE: THIS LIBRARY IS ONLY AVAILABLE UNDER UNIX.


-- Using ITIMER_VIRTUAL ------------------------------------------------

To load LIB * ITIMER_VIRTUAL, do

    uses itimer_virtual

To set the timer, do

    syssetvtimer(N)

This sets the timer for N/100 seconds of cpu time. (i.e. N is measured
in hundredth's of a second). When the specified time has elapsed, the
user-assignable procedure -vtimer_interrupt- is called. Its default
value is -identfn-.

Note: this is a one-off setting. If another timer setting is required,
-syssetvtimer- must be called again.

It is possible to set the timer and assign to -vtimer_interrupt- in one
go, by doing:

    syssetvtimer(N, P)

As above, the timer is set for N/100 seconds; also P is assigned to
-vtimer_interrupt-.

To cancel the timer, do

    syscanvtimer()


-- See also ------------------------------------------------------------

    MAN 2 SETITIMER
    REF * TIMES
    HELP * CLOCK
    LIB * PROFILE


--- C.unix/help/itimer_virtual
--- Copyright University of Sussex 1990. All rights reserved. ----------