TimeScheduler

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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

private static class TimeScheduler.IntTask
          Internal task class.

private class TimeScheduler.Loop
          The scheduler thread's main loop

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

private static class TimeScheduler.TaskQueue
          The task queue used by the scheduler.

Field Summary

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


private TimeScheduler.TaskQueue queue
          The task queue ordered according to task's next execution time

private static int RUN
          Thread is running
A call to start() has no effect on the thread
A call to stop() will stop the thread
A call to add() has no effect on the thread

private static int STOP
          Thread is stopped
A call to start() will recreate the thread
A call to stop() has no effect on the thread
A call to add() has no effect on the thread

private static int STOPPING
          A shutdown of the thread is in progress
A call to start() has no effect on the thread
A call to stop() has no effect on the thread
A call to add() has no effect on the thread

private static int SUSPEND
          Thread is suspended
A call to start() will recreate the thread
A call to stop() will switch the state from suspended to stopped
A call to add() will recreate the thread only if it is suspended

private long suspend_interval
          Time that task queue is empty before suspending the scheduling thread

private static long SUSPEND_INTERVAL
          Default suspend interval (ms)

private java.lang.Thread thread
          The scheduler thread

private static java.lang.String THREAD_NAME
          TimeScheduler thread name

private int thread_state
          The thread's running state

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

private void _run()
          If the task queue is empty, sleep until a task comes in or if slept for too long, suspend the thread.

private void _start()
          Set the thread state to running, create and start the thread

private void _stop()
          Set the thread state to stopped

private void _stopping()
          Set the thread state to stopping

private void _suspend()
          Set the thread state to suspended

private void _unsuspend()
          Restart the suspended thread

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

SUSPEND_INTERVAL

private static final long SUSPEND_INTERVAL

Default suspend interval (ms)

See Also:: Constant Field Values

RUN

private static final int RUN

Thread is running

A call to start() has no effect on the thread
A call to stop() will stop the thread
A call to add() has no effect on the thread

See Also:: Constant Field Values

SUSPEND

private static final int SUSPEND

Thread is suspended

A call to start() will recreate the thread
A call to stop() will switch the state from suspended to stopped
A call to add() will recreate the thread only if it is suspended

See Also:: Constant Field Values

STOPPING

private static final int STOPPING

A shutdown of the thread is in progress

A call to start() has no effect on the thread
A call to stop() has no effect on the thread
A call to add() has no effect on the thread

See Also:: Constant Field Values

STOP

private static final int STOP

Thread is stopped

A call to start() will recreate the thread
A call to stop() has no effect on the thread
A call to add() has no effect on the thread

See Also:: Constant Field Values

THREAD_NAME

private static final java.lang.String THREAD_NAME

TimeScheduler thread name

See Also:: Constant Field Values

thread

private java.lang.Thread thread

The scheduler thread

thread_state

private int thread_state

The thread's running state

suspend_interval

private long suspend_interval

Time that task queue is empty before suspending the scheduling thread

queue

private final TimeScheduler.TaskQueue queue

The task queue ordered according to task's next execution time

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

TimeScheduler

public TimeScheduler()

Create a scheduler that executes tasks in dynamically adjustable intervals

Method Detail

_start

private void _start()

Set the thread state to running, create and start the thread

_unsuspend

private void _unsuspend()

Restart the suspended thread

_suspend

private void _suspend()

Set the thread state to suspended

_stopping

private void _stopping()

Set the thread state to stopping

_stop

private void _stop()

Set the thread state to stopped

_run

private void _run()

If the task queue is empty, sleep until a task comes in or if slept for too long, suspend the thread.

Get the first task, if the running time hasn't been reached then wait a bit and retry. Else reschedule the task and then run it.

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

add

public void add(TimeScheduler.Task t)

Add a task for execution at adjustable intervals

size

public int size()

Answers 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.

Overview

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Deprecated

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Nested Class Summary
`private static class`	`TimeScheduler.IntTask` Internal task class.
`private class`	`TimeScheduler.Loop` The scheduler thread's main loop
`static interface`	`TimeScheduler.Task` The interface that submitted tasks must implement
`private static class`	`TimeScheduler.TaskQueue` The task queue used by the scheduler.

Field Summary
`protected static org.apache.commons.logging.Log`	`log`
`private TimeScheduler.TaskQueue`	`queue` The task queue ordered according to task's next execution time
`private static int`	`RUN` Thread is running A call to `start()` has no effect on the thread A call to `stop()` will stop the thread A call to `add()` has no effect on the thread
`private static int`	`STOP` Thread is stopped A call to `start()` will recreate the thread A call to `stop()` has no effect on the thread A call to `add()` has no effect on the thread
`private static int`	`STOPPING` A shutdown of the thread is in progress A call to `start()` has no effect on the thread A call to `stop()` has no effect on the thread A call to `add()` has no effect on the thread
`private static int`	`SUSPEND` Thread is suspended A call to `start()` will recreate the thread A call to `stop()` will switch the state from suspended to stopped A call to `add()` will recreate the thread only if it is suspended
`private long`	`suspend_interval` Time that task queue is empty before suspending the scheduling thread
`private static long`	`SUSPEND_INTERVAL` Default suspend interval (ms)
`private java.lang.Thread`	`thread` The scheduler thread
`private static java.lang.String`	`THREAD_NAME` TimeScheduler thread name
`private int`	`thread_state` The thread's running state

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
`private void`	`_run()` If the task queue is empty, sleep until a task comes in or if slept for too long, suspend the thread.
`private void`	`_start()` Set the thread state to running, create and start the thread
`private void`	`_stop()` Set the thread state to stopped
`private void`	`_stopping()` Set the thread state to stopping
`private void`	`_suspend()` Set the thread state to suspended
`private void`	`_unsuspend()` Restart the suspended thread
`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.

org.jgroups.util Class TimeScheduler

SUSPEND_INTERVAL

RUN

SUSPEND

STOPPING

STOP

THREAD_NAME

thread

thread_state

suspend_interval

queue

log

TimeScheduler

TimeScheduler

_start

_unsuspend

_suspend

_stopping

_stop

_run

setSuspendInterval

getSuspendInterval

dumpTaskQueue

add

add

size

start

stop

org.jgroups.util
Class TimeScheduler