org.jgroups.util
Class TimeScheduler

java.lang.Object
  org.jgroups.util.TimeScheduler

public class TimeScheduler
extends java.lang.Object

Fixed-delay & fixed-rate single thread scheduler

The scheduler supports varying scheduling intervals by asking the task every time for its next preferred scheduling interval. Scheduling can either be fixed-delay or fixed-rate. The notions are borrowed from java.util.Timer and retain the same meaning. I.e. in fixed-delay scheduling, the task's new schedule is calculated as:
new_schedule = time_task_starts + scheduling_interval

In fixed-rate scheduling, the next schedule is calculated as:
new_schedule = time_task_was_supposed_to_start + scheduling_interval

The scheduler internally holds a queue of tasks sorted in ascending order according to their next execution time. A task is removed from the queue if it is cancelled, i.e. if TimeScheduler.Task.isCancelled() returns true.

The scheduler internally uses a java.util.SortedSet to keep tasks sorted. java.util.Timer uses an array arranged as a binary heap that doesn't shrink. It is likely that the latter arrangement is faster.

Initially, the scheduler is in SUSPENDed mode, start() need not be called: if a task is added, the scheduler gets started automatically. Calling start() starts the scheduler if it's suspended or stopped else has no effect. Once stop() is called, added tasks will not restart it: start() has to be called to restart the scheduler.

Nested Class Summary

static interface	TimeScheduler.CancellableTask
static interface	TimeScheduler.Task The interface that submitted tasks must implement

Field Summary

protected static org.apache.commons.logging.Log

log

Constructor Summary

TimeScheduler()
Create a scheduler that executes tasks in dynamically adjustable intervals

TimeScheduler(long suspend_interval)
Create a scheduler that executes tasks in dynamically adjustable intervals

Method Summary

void	add(TimeScheduler.Task t) Add a task for execution at adjustable intervals
void	add(TimeScheduler.Task t, boolean relative) Add a task for execution at adjustable intervals
java.lang.String	dumpTaskQueue()
long	getSuspendInterval()
void	setSuspendInterval(long s)
int	size() Answers the number of tasks currently in the queue.
void	start() Start the scheduler, if it's suspended or stopped
void	stop() Stop the scheduler if it's running.

Methods inherited from class java.lang.Object

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

Field Detail

log

protected static final org.apache.commons.logging.Log log

Constructor Detail

TimeScheduler

public TimeScheduler(long suspend_interval)

Create a scheduler that executes tasks in dynamically adjustable intervals

Parameters:

suspend_interval - the time that the scheduler will wait for at least one task to be placed in the task queue before suspending the scheduling thread

TimeScheduler

public TimeScheduler()

Create a scheduler that executes tasks in dynamically adjustable intervals

Method Detail

setSuspendInterval

public void setSuspendInterval(long s)

getSuspendInterval

public long getSuspendInterval()

dumpTaskQueue

public java.lang.String dumpTaskQueue()

add

public void add(TimeScheduler.Task t,
                boolean relative)

Add a task for execution at adjustable intervals

Parameters:

t - the task to execute

relative - scheduling scheme:

true:
Task is rescheduled relative to the last time it actually started execution

false:
Task is scheduled relative to its last execution schedule. This has the effect that the time between two consecutive executions of the task remains the same.

add

public void add(TimeScheduler.Task t)

Add a task for execution at adjustable intervals

Parameters:

t - the task to execute

size

public int size()

Answers the number of tasks currently in the queue.

Returns:

The number of tasks currently in the queue.

start

public void start()

Start the scheduler, if it's suspended or stopped

stop

public void stop()
          throws java.lang.InterruptedException

Stop the scheduler if it's running. Switch to stopped, if it's suspended. Clear the task queue.

Throws:

java.lang.InterruptedException - if interrupted while waiting for thread to return