From: John Labovitz <johnl@...>
Date: 2005-05-19T02:46:00+09:00
Subject: Re: Event scheduler in Ruby

On May 18, 2005, at 12:50 AM, Lawrence Oluyede wrote:

> Is there anything like the sched module in Python?
> http://docs.python.org/lib/module-sched.html

I've written a Scheduler class for a project I'm working on.  Perhaps  
it might help.

I haven't packed it up yet, but I'll include the code below.  If  
there's interest, I could publish it somewhere.

#<-- CUT HERE
#-- this is schedule.rb
=begin

= Scheduler

Schedules tasks in a cron-like manner, but uses a nearly-English  
syntax for scheduling tasks.
It uses threads to do the waiting, although the tasks themselves are  
run sequentially in the main thread.

Note that it doesn't handle absolute times or dates (eg, 'at 3.pm',  
'on 2005-05-18') yet.
It would also be nice to handle +Runt+ objects.

== Example

   class MyScheduler < Scheduler

     def schedule

       at startup do
         do_my_startup_task
       end

       at shutdown do
         do_my_shutdown_task
       end

       every minute do
         do_something_frequently
       end

       every 2.hours do
         do_something_occasionally
       end

     end

   end

   sched = MyScheduler.new
   sched.start

   # or to run it only for one hour...

   sched.start(1.hour)

== Author

John Labovitz <johnl@johnlabovitz.com>

=end

require 'timeunits'    # see below
require 'time'
require 'thread'


#
# A +Scheduler+ object keeps track of tasks to be run.  Usual usage  
is to subclass Scheduler, and
# define your own +schedule+ method to set up the schedule.  Once  
you've created a new Scheduler
# object, you can call +start+ to start the schedule running.

class Scheduler

   #
   # A +Task+ represents something to do after an interval of time  
has happened.

   class Task

     #
     # The amount of time to wait until the task will be run.  If  
this is set to the symbol
     # +:startup+ or +:shutdown+, the task will be run only once, at  
schedule startup or
     # shutdown, respectively.
     #
     # FIXME: It would be nice if +interval+ could be a +Time+ or  
+Date+ object, or a crontab-like
     # string, or a +Runt::Event+.

     attr_accessor :interval

     #
     # A block or Proc object that will be run when the time interval  
has passed.

     attr_accessor :proc

     #
     # The internal thread that is responsible for actually waiting  
the time interval.

     attr_accessor :thread

     #
     # Create a new task.  If supplied, +interval+ and +proc+  
correspond to their
     # respective methods.

     def initialize(interval=nil, proc=nil)
       self.interval = interval
       self.proc = proc
       self.thread = nil
     end

     #
     # Run the block or Proc associated with a task.

     def run
       self.proc.call
     end

     #
     # Schedule the task.  This actually starts a thread that waits  
until the specified
     # time interval has passed, then adds the task to a run queue  
that the main +Scheduler+
     # object waits on.

     def schedule(scheduler)
       case self.interval
       when :startup, :shutdown
         # ignore it
       else
         self.thread = Thread.new do
           loop do
             sleep self.interval
             scheduler.run_queue << self
           end
         end
         self.thread.abort_on_exception = true
       end
     end

   end


   #
   # The list of all tasks in the schedule, including startup and  
shutdown tasks.

   attr_accessor :tasks

   #
   # The run-queue, representing all the tasks whose interval has  
passed, and should be run.

   attr_accessor :run_queue

   #
   # Create a new schedule.  The object's +#schedule+ method, if any,  
will be called to create
   # the schedule.  Note that the schedule's +#run+ method must be  
called to get actually start
   # the schedule.

   def initialize
     self.tasks = Array.new
     self.run_queue = Queue.new
     self.schedule
   end

   #
   # Add a task to the schedule.  If +interval+ is a number (Fixnum  
or Float), it represents the
   # number of seconds to wait between successive runs of the task.   
If +interval+ is a Time or Date
   # object, the task will be run once at the specified time.

   def add_task(interval, &block)
     tasks << Task.new(interval, block)
   end

   #
   # Return all tasks that should be run at startup.

   def startup_tasks
     self.tasks.select { |t| t.interval == :startup }
   end

   #
   # Return all tasks that should be run at shutdown.

   def shutdown_tasks
     self.tasks.select { |t| t.interval == :shutdown }
   end

   #
   # Return all tasks that should be scheduled.

   def scheduled_tasks
     self.tasks.select { |t| t.interval != :startup && t.interval ! 
= :shutdown }
   end

   #
   # Various helpful aliases that encourage readable schedules.

   def second;   1.second;   end
   def minute;   1.minute;   end
   def hour;     1.hour;     end
   def day;      1.day;      end

   def startup;  :startup;   end
   def shutdown; :shutdown;  end

   alias every add_task
   alias at    every
   alias on    every

   #
   # Set up schedules.  This method should be implemented by a  
subclass of Scheduler.

   def schedule
     # implemented by subclass
   end

   #
   # Start a schedule.  If +period+ is supplied, the schedule will  
only run for that
   # many seconds.  Otherwise, it will run forever, or until there  
are no tasks to run.

   def start(period=nil)

     #
     # Run any startup tasks.

     self.startup_tasks.each { |t| t.run }

     #
     # If caller only wants to run for a while, start a thread that will
     # sleep that long, then kill off all the threads.  +nil+ is  
posted to
     # the queue as a signal that the scheduler should stop running.

     if period
       Thread.new do
         Thread.abort_on_exception = true
         sleep period
         self.scheduled_tasks.each { |t| t.thread.exit if t.thread &&  
t.thread.alive? }
         self.run_queue << nil
       end
     end

     #
     # Schedule all the tasks.

     self.scheduled_tasks.each { |t| t.schedule(self) }

     #
     # Run any tasks whose threads have placed the task onto the run  
queue, until +nil+ is received.

     while (task = self.run_queue.pop) do
       task.run
     end

     #
     # Run any shutdown tasks.

     self.shutdown_tasks.each { |t| t.run }

   end

end

#<-- CUT HERE
#--this is timeunits.rb
module TimeUnits
   def second; self            ; end
   def minute; self * 60       ; end
   def hour;   self.minute * 60; end
   def day;    self.hour * 24  ; end

   alias :seconds  :second
   alias :minutes  :minute
   alias :hours    :hour
   alias :days     :day
end

class Fixnum
   include TimeUnits
end

class Float
   include TimeUnits
end

#<-- CUT HERE


--
John Labovitz
Macintosh support, research, and software development
John Labovitz Consulting, LLC
johnl@johnlabovitz.com |  +1 503.949.3492 | www.johnlabovitz.com/ 
consulting