ref: 54bac038f411c10a596adf84c06df32f8c7c4c53
dir: /man/2/timers/
.TH TIMERS 2
.SH NAME
timers \- interval timers
.SH SYNOPSIS
.EX
include "timers.m";
timers := load Timers Timers->PATH;
Timer: adt
{
timeout: chan of int;
start: fn(msec: int): ref Timer;
stop: fn(t: self ref Timer);
};
init: fn(minms: int): int;
shutdown: fn();
.EE
.SH DESCRIPTION
.B Timers
provides simple interval timing.
Timeouts are notified by a message sent on a channel,
allowing them to provide timeouts in
.B alt
statements.
.PP
The module must first be initialised by calling
.BR init ,
which starts a process to manage the interval timers and returns its process ID.
Before exit, the caller must shut the timing process down either by calling
.BR shutdown ,
which stops it synchronously; by using the process ID returned by
.B init
to kill it;
or by killing the process group of the process that
called
.BR init
(since the timing processes remain in that group).
.I Minms
gives the minimum granularity of timing requests in milliseconds.
.TP
.BI Timer.start( msec )
Returns a
.B Timer
that will expire in
.I msec
milliseconds,
measured with the granularity of either
.IR sys-sleep (2)
or the granularity set by
.BR init ,
whichever is greater.
.TP
.IB t .timeout
An arbitrary integer value is sent on this channel when the timer
.I t
expires.
.TP
.IB t .stop()
The timer
.I t
is stopped
and removed from the interval timing queue,
if it has not already expired.
.PP
Each
.B Timer
value times a single interval.
When a timer
.I t
expires, the timing process attempts, at that and each subsequent timing interval, to send on
.IB t .timeout
until the expiry message is delivered or the timer is stopped.
.SH EXAMPLE
Wait for data to be sent on an input channel, but give up if it does not arrive within 600 milliseconds:
.IP
.EX
t := Timer.start(600);
alt {
data := <-input =>
t.stop();
# process the data
<-t.timeout =>
# request timed out
}
.EE
.SH SEE ALSO
.IR sys-millisec (2),
.IR sys-sleep (2)