alma.ACS.jbaci

Class BACITimer

java.lang.Object

alma.ACS.jbaci.BACITimer

public class BACITimer
extends java.lang.Object

BACI timer. Based on EDU.oswego.cs.dl.util.concurrent (it was not approriate for BACI usage). Timer tasks should complete quickly. If a timer task takes excessive time to complete, it "hogs" the timer's task execution thread. This can, in turn, delay the execution of subsequent tasks, which may "bunch up" and execute in rapid succession when (and if) the offending task finally completes.

Author:

Matej Sekoranja

See Also:

EDU.oswego.cs.dl.util.concurrent

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	BACITimer.RunLoop The runloop is isolated in its own Runnable class just so that the main class need not implement Runnable, which would allow others to directly invoke run, which is not supported.
protected static class	BACITimer.TaskNode
static interface	BACITimer.TimerRunnable Timer runnable interface.

Field Summary

Fields

Modifier and Type	Field and Description
protected Heap	heap_ tasks are maintained in a standard priority queue
protected BACITimer.RunLoop	runLoop_
protected boolean	shutdown_ shutdown status flag
protected java.lang.Thread	thread_ The thread used to process commands
protected java.util.concurrent.ThreadFactory	threadFactory_ thread factory, can be null

Constructor Summary

Constructors

Constructor and Description
BACITimer(java.util.concurrent.ThreadFactory threadFactory) Constructor.

Method Summary

Modifier and Type	Method and Description
static void	cancel(java.lang.Object taskID) Cancel a scheduled task that has not yet been run.
protected void	clearThread() set thread_ to null to indicate termination
java.lang.Object	executeAfterDelay(long millisecondsToDelay, BACITimer.TimerRunnable command) Excecute the given command after waiting for the given delay.
java.lang.Object	executeAt(java.util.Date date, BACITimer.TimerRunnable command) Execute the given command at the given time.
java.lang.Object	executePeriodically(long period, BACITimer.TimerRunnable command, long firstTime) Execute the given command every period milliseconds AT FIXED RATE.
java.lang.Thread	getThread() Return the thread being used to process commands, or null if there is no such thread.
protected BACITimer.TaskNode	nextTask() Return the next task to execute, or null if thread is interrupted
protected void	restart() Start (or restart) a thread to process commands, or wake up an existing thread if one is already running.
void	shutDown() Cancel all tasks and interrupt the background thread executing the current task, if any.

Methods inherited from class java.lang.Object

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

Field Detail

heap_

protected final Heap heap_

tasks are maintained in a standard priority queue

threadFactory_

protected final java.util.concurrent.ThreadFactory threadFactory_

thread factory, can be null

shutdown_

protected volatile boolean shutdown_

shutdown status flag

thread_

protected java.lang.Thread thread_

The thread used to process commands

runLoop_

protected final BACITimer.RunLoop runLoop_

Constructor Detail

BACITimer

public BACITimer(java.util.concurrent.ThreadFactory threadFactory)

Constructor.

Parameters:

threadFactory - thread factory to be used to create thread, if null no factory is being used

Method Detail

executeAt

public java.lang.Object executeAt(java.util.Date date,
                                  BACITimer.TimerRunnable command)

Execute the given command at the given time.

Parameters:

date - -- the absolute time to run the command, expressed as a java.util.Date.

command - -- the command to run at the given time.

Returns:

taskID -- an opaque reference that can be used to cancel execution request

executeAfterDelay

public java.lang.Object executeAfterDelay(long millisecondsToDelay,
                                          BACITimer.TimerRunnable command)

Excecute the given command after waiting for the given delay.

Parameters:

millisecondsToDelay - -- the number of milliseconds from now to run the command.

command - -- the command to run after the delay.

Returns:

taskID -- an opaque reference that can be used to cancel execution request

executePeriodically

public java.lang.Object executePeriodically(long period,
                                            BACITimer.TimerRunnable command,
                                            long firstTime)

Execute the given command every period milliseconds AT FIXED RATE. If startNow is true, execution begins immediately, otherwise, it begins after the first period delay.

Parameters:

period - -- the period, in milliseconds. Periods are measured from start-of-task to the next start-of-task. It is generally a bad idea to use a period that is shorter than the expected task duration.

command - -- the command to run at each cycle

firstTime - -- time when task should start with execution, 0 means immediately.

Returns:

taskID -- an opaque reference that can be used to cancel execution request

Throws:

java.lang.IllegalArgumentException - if period less than or equal to zero.

cancel

public static void cancel(java.lang.Object taskID)

Cancel a scheduled task that has not yet been run. The task will be cancelled upon the next opportunity to run it. This has no effect if this is a one-shot task that has already executed. Also, if an execution is in progress, it will complete normally. (It may however be interrupted via getThread().interrupt()). But if it is a periodic task, future iterations are cancelled.

Parameters:

taskID - -- a task reference returned by one of the execute commands

Throws:

java.lang.ClassCastException - if the taskID argument is not of the type returned by an execute command.

getThread

public java.lang.Thread getThread()

Return the thread being used to process commands, or null if there is no such thread. You can use this to invoke any special methods on the thread, for example, to interrupt it.

clearThread

protected void clearThread()

set thread_ to null to indicate termination

restart

protected void restart()

Start (or restart) a thread to process commands, or wake up an existing thread if one is already running. This method can be invoked if the background thread crashed due to an unrecoverable exception in an executed command.

shutDown

public void shutDown()

Cancel all tasks and interrupt the background thread executing the current task, if any. A new background thread will be started if new execution requests are encountered. If the currently executing task does not repsond to interrupts, the current thread may persist, even if a new thread is started via restart().

nextTask

protected BACITimer.TaskNode nextTask()

Return the next task to execute, or null if thread is interrupted