[Webware-discuss] RFC: Simple Task Scheduling Proposal

[Tom S. <tom...@li...>]

In the last discussions we touched implicitely some
task scheduling questions. I looked at the Application.py
code to search for a place, where one could
plug that in (better than a TaskKit?), because I think 
this could become important for many things. You
can do it with OS mechnism, but to have it crossplattform
in the application framework would be really nice and 
a great plus.

###########################################################
One scheduling example is realized for Sessions:

in __init__.py you have

if useSessionSweeper:
  self.startSessionSweeper()

def startSessionSweeper(self):
def sweepSessionsContinuously(self,close):
def sweepSessions(self):

###########################################################
Let's make this more general (Task seems a good name). 
Look at the following python code + pseudocode,
where I just show what I have in mind, not
every detail (sleeping time, ...)

Application(self,....,useTasks=1,..)

def __init(self,...)
  if useTasks:
    self._tasks = get tasklist from Application.config
                  or by a name convention *Task.py
    self.startTasks() 
 
    # possible Tasks: 
    #  * Session, 
    #  * Scheduling of "Webware cronjobs"
    #  * Generate static pages
    #  * update in memory information


def startTasks(self): 
  #self._tasks could also be a parameter
  for task in self._tasks:
    task.run(app, close)

class Task:
  def run(self, app, close):
  # for Session this is called
  # sweepSessionsContinuously: 
  # there you need app.running, app.sessions(),

class SessionSweepTask(Task):
  def run(self, app, close):
    while self.running:
      self.sweepSessions()
      try:
        close.wait(self.setting('SessionTimeout')*60/10.0)
      except IOError:
        pass

  def sweepSessions(self, app):
    sessions = app.sessions()
    ...

class CalendarTask(Task): 
  # this is for tasks which run once or
  # no seldom. use a Task subclass if
  # your task ha to be scheduled often 
  #(e.g. every Minute..)
  # use mxDateTime for this kind of stuff
  def run(self, app, close):

class PageWriterTask(Task):
  def run((self, app, close):
    #generate staic pages

###########################################################
in Application.config use:

'Tasks':  ['SessionSweep', 'Calendar', 'PageWriter'],

###########################################################

hey, hope you like this proposal. I'm sure I forgot something,
but it looks ok afrer reading it several times :-)

The amazing thing with Webware ist, that you can go down
to the framework, understand and even change it. After 2 years 
of Zope programming I still have no idea how it works under 
the hood!

-- 

Tom Schwaller
http://www.linux-community.de