TaskHandler.py

from time import time
from threading import Thread


class TaskHandler(object):
    """The task handler.

    While the Task class only knows what task to perform with the run()-method,
    the TaskHandler has all the knowledge about the periodicity of the task.
    Instances of this class are managed by the Scheduler in the scheduled,
    running and onDemand dictionaries.
    """


    ## Init ##

    def __init__(self, scheduler, start, period, task, name):
        self._scheduler = scheduler
        self._task = task
        self._name = name
        self._thread = None
        self._isRunning = False
        self._suspend = False
        self._lastTime = None
        self._startTime = start
        self._registerTime = time()
        self._reregister = True
        self._rerun = False
        self._period = abs(period)
        self._isOnDemand = False

    ## Scheduling ##

    def reset(self, start, period, task, reregister):
        self._startTime = start
        self._period = abs(period)
        self._task = task
        self._reregister = reregister

    def runTask(self):
        """Run this task in a background thread."""
        if self._suspend:
            self._scheduler.notifyCompletion(self)
            return
        self._rerun = False
        self._thread = Thread(None, self._task._run, self.name(), (self,))
        self._isRunning = True
        self._thread.start()

    def reschedule(self):
        """Determine whether this task should be rescheduled.

        Increments the startTime and returns true if this is
        a periodically executed task.
        """
        if self._period == 0 or not self._reregister:
            return False
        else:
            if self._lastTime - self._startTime > self._period:
                # if the time taken to run the task exceeds the period
                self._startTime = self._lastTime + self._period
            else:
                self._startTime += self._period
            return True

    def notifyCompletion(self):
        self._isRunning = False
        self._lastTime = time()
        self._scheduler.notifyCompletion(self)

    def notifyFailure(self):
        self._isRunning = False
        self._lastTime = time()
        self._scheduler.notifyFailure(self)


    ## Attributes ##

    def isRunning(self):
        return self._isRunning

    def runAgain(self):
        """Determine whether this task should be run again.

        This method lets the Scheduler check to see whether this task should be
        re-run when it terminates.
        """
        return self._rerun

    def isOnDemand(self):
        """Return True if this task is not scheduled for periodic execution."""
        return self._isOnDemand

    def setOnDemand(self, onDemand=True):
        self._isOnDemand = bool(onDemand)

    def runOnCompletion(self):
        """Request that this task be re-run after its current completion.

        Intended for on-demand tasks that are requested by the Scheduler while
        they are already running.
        """
        self._rerun = True

    def unregister(self):
        """Request that this task not be kept after its current completion.

        Used to remove a task from the scheduler.
        """
        self._reregister = False
        self._rerun = False

    def disable(self):
        """Disable future invocations of this task."""
        self._suspend = True

    def enable(self):
        """Enable future invocations of this task."""
        self._suspend = False

    def period(self):
        """Return the period of this task."""
        return self._period

    def setPeriod(self, period):
        """Change the period for this task."""
        self._period = period

    def stop(self):
        self._isRunning = False

    def name(self):
        return self._name

    def startTime(self, newTime=None):
        if newTime:
            self._startTime = newTime
        return self._startTime