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timers - interval timers


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();


Timers provides simple interval timing. Timeouts are notified by a message sent on a channel, allowing them to provide timeouts in alt statements.

The module must first be initialised by calling 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 shutdown, which stops it synchronously; by using the process ID returned by init to kill it; or by killing the process group of the process that called init (since the timing processes remain in that group). Minms gives the minimum granularity of timing requests in milliseconds.

Returns a Timer that will expire in msec milliseconds, measured with the granularity of either sys-sleep(2) or the granularity set by init, whichever is greater.
An arbitrary integer value is sent on this channel when the timer t expires.
The timer t is stopped and removed from the interval timing queue, if it has not already expired.

Each Timer value times a single interval. When a timer t expires, the timing process attempts, at that and each subsequent timing interval, to send on t.timeout until the expiry message is delivered or the timer is stopped.


Wait for data to be sent on an input channel, but give up if it does not arrive within 600 milliseconds:

t := Timer.start(600);
alt {
data := <-input =>
	# process the data
<-t.timeout =>
	# request timed out


sys-millisec(2), sys-sleep(2)

TIMERS(2 ) Rev:  Mon Nov 03 06:22:13 GMT 2008