com.sun.sgs.impl.kernel.schedule
Class WindowSchedulerQueue

java.lang.Object
  com.sun.sgs.impl.kernel.schedule.WindowSchedulerQueue

All Implemented Interfaces:

TimedTaskListener, SchedulerQueue

public class WindowSchedulerQueue
extends Object
implements SchedulerQueue, TimedTaskListener

This implementation of SchedulerQueue tries to provide fairness between users without taking too long to service any given user's tasks. This is typified by the phrase "no one gets seconds until everyone who wants them has had firsts."

The implementation uses a priority queue, keyed off what is called a window value. Users submit tasks into increasing window values, and may never submit tasks into windows that have already passed.

Constructor Summary

WindowSchedulerQueue(Properties properties)
Creates an instance of WindowSchedulerQueue.

Method Summary

void	addTask(ScheduledTask task) Adds a task to the scheduler.
RecurringTaskHandle	createRecurringTaskHandle(ScheduledTask task) Creates a RecurringTaskHandle for the associated task.
ScheduledTask	getNextTask(boolean wait) Returns the next task to run, blocking if wait is true.
int	getNextTasks(Collection<? super ScheduledTask> tasks, int max) Places at most the next max tasks available into the provided Collection.
int	getReadyCount() Returns the number of tasks that are ready to run.
void	notifyCancelled(ScheduledTask task) Notifies the scheduler that the given task has been cancelled.
TaskReservation	reserveTask(ScheduledTask task) Reserves a space for a task.
void	shutdown() Tells this SchedulerQueue to shutdown.
void	timedTaskReady(ScheduledTask task) Called when a delayed task has reached its time to run.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WindowSchedulerQueue

public WindowSchedulerQueue(Properties properties)

Creates an instance of WindowSchedulerQueue.

Parameters:

properties - the application Properties

Method Detail

getReadyCount

public int getReadyCount()

Returns the number of tasks that are ready to run. This does not include any pending or recurring tasks that have not yet come time to run.

Specified by:

getReadyCount in interface SchedulerQueue

Returns:

the number of tasks ready to run

getNextTask

public ScheduledTask getNextTask(boolean wait)
                          throws InterruptedException

Returns the next task to run, blocking if wait is true. If not waiting, it returns null if nothing is available.

Specified by:

getNextTask in interface SchedulerQueue

Parameters:

wait - whether to wait for a task to become available

Returns:

the next ScheduledTask or null

Throws:

InterruptedException - if the thread is interrupted while waiting for a task

getNextTasks

public int getNextTasks(Collection<? super ScheduledTask> tasks,
                        int max)

Places at most the next max tasks available into the provided Collection. This method does not block, so it may not provide any tasks. The number of tasks provided is returned.

Note that there is no guarentee that the tasks provided are all contiguous. That is, if two calls are made at the same time to this method, or a call to getNextTask is made at the same time, the scheduler does not have to provide the next max tasks to one consumer before servicing others. If this behavior is needed, the caller needs to synchronize access. The tasks are guaranteed to be in correct order if the provided Collection is ordered.

Specified by:

getNextTasks in interface SchedulerQueue

Parameters:

tasks - the Collection into which the tasks are put

max - the maximum number of tasks to get

Returns:

the number of tasks provided

reserveTask

public TaskReservation reserveTask(ScheduledTask task)

Reserves a space for a task.

Specified by:

reserveTask in interface SchedulerQueue

Parameters:

task - the ScheduledTask to reserve

Returns:

a TaskReservation for the task

addTask

public void addTask(ScheduledTask task)

Adds a task to the scheduler. This task is executed only once, but may be executed immediately or in the future.

Note that if this is a recurring task, then a call to its getRecurringTaskHandle method must return a handle provided by a call to this implementation's createRecurringTaskHandle method. Note also that it is up to the caller to re-schedule this task for each recurrence, and that each such call must provide a unique instance of ScheduledTask.

Specified by:

addTask in interface SchedulerQueue

Parameters:

task - the ScheduledTask to add

createRecurringTaskHandle

public RecurringTaskHandle createRecurringTaskHandle(ScheduledTask task)

Creates a RecurringTaskHandle for the associated task. The associated task will not actually be available through this queue until start is called on the returned handle. The ScheduledTask instance must never have been previously used to schedule a recurring task. Note that after the initial execution of this task, it is up to the caller to schedule each recurrence through a call to addTask.

Specified by:

createRecurringTaskHandle in interface SchedulerQueue

Parameters:

task - the ScheduledTask to run recurringly

Returns:

a RecurringTaskHandle that manages the task

notifyCancelled

public void notifyCancelled(ScheduledTask task)

Notifies the scheduler that the given task has been cancelled. An implementation does not need to do anything in reaction to this call as long as the given task will not run. If this task is unknown, or has already run, this call may be ignored.

Specified by:

notifyCancelled in interface SchedulerQueue

Parameters:

task - the ScheduledTask that has been cancelled

timedTaskReady

public void timedTaskReady(ScheduledTask task)

Called when a delayed task has reached its time to run.

Specified by:

timedTaskReady in interface TimedTaskListener

Parameters:

task - the ScheduledTask that is ready to run

shutdown

public void shutdown()

Tells this SchedulerQueue to shutdown.

Specified by:

shutdown in interface SchedulerQueue