ufo-timer

Implementing timer requires thread mechanism, and this feature is not always supported in scheme. All I now know is SRFI-120 provide timer based on SRFI-18, which is an implementation of POSIX thread model. However, SRFI-18 released on 2001. Although Chez Scheme also implements POSIX thread, it opened source much latter, and never claims to be consistent with SRFI-18. This makes SRFI-120 not portable to Chez Scheme.

This repository is a timer implementation based on Chez Scheme's thread mechanism. And before importing this repository, please firstly (import (chezscheme)).

Prerequire

Chez Scheme and AKKU. In addition, though Chez Scheme claims its thread mechanism portable to Windows, I've not done any tests on this point.

Example

(import (ufo-timer)) to use timer.

Print "test" after 5 seconds,

(let ([timer 
        (init-timer 
            (make-time 'time-duration 0 5) 
            (lambda () (pretty-print 'test)))])
    (start-timer timer))

NOTE: (make-time 'time-duration 0 5) is to make Chez Scheme's time object.

Repeat "test" with 5-seconds interval

(let ([timer 
        (init-interval-timer 
            (make-time 'time-duration 0 5) 
            (lambda () (pretty-print 'test)))])
    (start-timer timer))

Advanced features

Thread pool

This repository is based on ufo-thread-pool, and users can also assign a pool to timers like following:

1. (init-timer timeout todo pool)
2. (init-interval-timer timeout todo stop pool)

NOTE: you need to additionally (import (ufo-thread-pool)).

For more related description, please refer to other cases in this text.

Stop interval timer

As shown above, interval timer have a stop parameter which is default (lambda () #t) and such interval timer will never stop. If you want it to react to some condition, such as stopping when reach 3 times, following closure will help a lot:

(let* ([i 0]
        [timer 
        (init-interval-timer 
            (make-time 'time-duration 0 5) 
            (lambda () 
                (set! i (+ 1 i))
                (pretty-print 'test))
            (lambda () (< i 3)))])
    (start-timer timer))

Set expire time

When users do some socket programming, it's very often to set expire time. Or in other words, if a socket is inactive for server seconds, it will be closed by a timer.

(let ([timer 
        (init-interval-timer 
            (make-time 'time-duration 0 5) 
            (lambda () (pretty-print 'try-to-close-socket)))])
    (start-timer timer)
    (with-mutex (timer-mutex timer)
        ;Here's usually a loop body
        ;during the body, you can reset the timer to initial state by following
        (condition-broadcast (timer-condition timer))))