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org.apache.derby.impl.services.daemon
Class BasicDaemon  

java.lang.Object
  org.apache.derby.impl.services.daemon.BasicDaemon

All Implemented Interfaces:

org.apache.derby.iapi.services.daemon.DaemonService, java.lang.Runnable

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public class BasicDaemon

extends java.lang.Object

implements org.apache.derby.iapi.services.daemon.DaemonService, java.lang.Runnable

A BasicDaemon is a background worker thread which does asynchronous I/O and general clean up. It should not be used as a general worker thread for parallel execution. One cannot count on the order of request or count on when the daemon will wake up, even with serviceNow requests. Request are not persistent and not recoverable, they are all lost when the system crashes or is shutdown. System shutdown, even orderly ones, do not wait for daemons to finish its work or empty its queue. Furthermore, any Serviceable subscriptions, including onDemandOnly, must tolerate spurrious services. The BasicDaemon will setup a context manager with no context on it. The Serviceable object's performWork must provide useful context on the context manager to do its work. The BasicDaemon will wrap performWork call with try / catch block and will use the ContextManager's error handling to clean up any error. The BasicDaemon will guarentee serviceNow request will not be lost as long as the jbms does not crash - however, if N serviceNow requests are made by the same client, it may only be serviced once, not N times. Many Serviceable object will subscribe to the same BasicDaemon. Their performWork method should be well behaved - in other words, it should not take too long or hog too many resources or deadlock with anyone else. And it cannot (should not) error out. The BasicDaemon implementation manages the DaemonService's data structure, handles subscriptions and enqueues requests, and determine the service schedule for its Serviceable objects. The BasicDaemon keeps an array (Vector) of Serviceable subscriptions it also keeps 2 queues for clients that uses it for one time service - the 1st queue is for a serviceNow enqueue request, the 2nd queue is for non serviceNow enqueue request. This BasicDaemon services its clients in the following order: 1. any subscribed client that have made a serviceNow request that has not been fulfilled 2. serviceable clients on the 1st queue 3. all subscribed clients that are not onDemandOnly 4. serviceable clients 2nd queue

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Field Summary
private  boolean	awakened
protected  org.apache.derby.iapi.services.context.ContextManager	contextMgr
protected  org.apache.derby.iapi.services.context.ContextService	contextService
private  int	earlyWakeupCount
private  java.util.List	highPQ           Queues for the work to be done.
private  boolean	inPause
private  long	lastServiceTime
private  int	nextService           which subscribed clients to service next? only accessed by daemon thread
private  java.util.List	normPQ
private  int	numClients
private static int	OPTIMAL_QUEUE_SIZE
private  boolean	running
private  boolean	stopped
private  boolean	stopRequested
private  java.util.Vector	subscription
private  boolean	waiting           true if I'm waiting, if this is false then I am running and a notify is not required.

 

Fields inherited from interface org.apache.derby.iapi.services.daemon.DaemonService

DaemonOff, DaemonTrace, TIMER_DELAY

 

Constructor Summary

BasicDaemon(org.apache.derby.iapi.services.context.ContextService contextService)           make a BasicDaemon

 

Method Summary
void	clear()           Get rid of all queued up Serviceable tasks.
boolean	enqueue(org.apache.derby.iapi.services.daemon.Serviceable newClient, boolean serviceNow)           Request a one time service from the Daemon.
private  boolean	inPause()
protected  ServiceRecord	nextAssignment(boolean urgent)
void	pause()           Pause.
private  boolean	rest()           Returns true if awakened by some notification, false if wake up by timer
void	resume()           Resume service after a pause
void	run()           This method will be called by whoever wishes to run your class implementing Runnable.
protected  void	serviceClient(ServiceRecord clientRecord)
void	serviceNow(int clientNumber)           Service this subscription ASAP.
void	stop()           Finish what we are doing and at the next convenient moment, get rid of the thread and make the daemon object goes away if possible.
private  boolean	stopRequested()
int	subscribe(org.apache.derby.iapi.services.daemon.Serviceable newClient, boolean onDemandOnly)           Add a new client that this daemon needs to service
void	unsubscribe(int clientNumber)           Get rid of a client from the daemon.
void	waitUntilQueueIsEmpty()
protected  void	wakeUp()
private  void	work(boolean urgentOnly)
private  void	yield()

 

Methods inherited from class java.lang.Object

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

 

Field Detail

numClients

private int numClients

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OPTIMAL_QUEUE_SIZE

private static final int OPTIMAL_QUEUE_SIZE

See Also:

Constant Field Values

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subscription

private final java.util.Vector subscription

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contextService

protected final org.apache.derby.iapi.services.context.ContextService contextService

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contextMgr

protected final org.apache.derby.iapi.services.context.ContextManager contextMgr

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highPQ

private final java.util.List highPQ

Queues for the work to be done. These are synchronized by this object.

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normPQ

private final java.util.List normPQ

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nextService

private int nextService

which subscribed clients to service next? only accessed by daemon thread

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awakened

private boolean awakened

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waiting

private boolean waiting

true if I'm waiting, if this is false then I am running and a notify is not required.

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inPause

private boolean inPause

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running

private boolean running

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stopRequested

private boolean stopRequested

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stopped

private boolean stopped

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lastServiceTime

private long lastServiceTime

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earlyWakeupCount

private int earlyWakeupCount

Constructor Detail

BasicDaemon

public BasicDaemon(org.apache.derby.iapi.services.context.ContextService contextService)

make a BasicDaemon

Method Detail

subscribe

public int subscribe(org.apache.derby.iapi.services.daemon.Serviceable newClient,
                     boolean onDemandOnly)

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Add a new client that this daemon needs to service

Specified by:

subscribe in interface org.apache.derby.iapi.services.daemon.DaemonService

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unsubscribe

public void unsubscribe(int clientNumber)

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Get rid of a client from the daemon.

Specified by:

unsubscribe in interface org.apache.derby.iapi.services.daemon.DaemonService

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serviceNow

public void serviceNow(int clientNumber)

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Service this subscription ASAP. Does not guarantee that the daemon will actually do anything about it.

Specified by:

serviceNow in interface org.apache.derby.iapi.services.daemon.DaemonService

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enqueue

public boolean enqueue(org.apache.derby.iapi.services.daemon.Serviceable newClient,
                       boolean serviceNow)

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Request a one time service from the Daemon. Unless performWork returns REQUEUE (see Serviceable), the daemon will service this client once and then it will get rid of this client. Since no client number is associated with this client, it cannot request to be serviced or be unsubscribed. The work is always added to the deamon, regardless of the state it returns.

Specified by:

enqueue in interface org.apache.derby.iapi.services.daemon.DaemonService

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clear

public void clear()

Get rid of all queued up Serviceable tasks.

Specified by:

clear in interface org.apache.derby.iapi.services.daemon.DaemonService

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nextAssignment

protected ServiceRecord nextAssignment(boolean urgent)

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serviceClient

protected void serviceClient(ServiceRecord clientRecord)

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run

public void run()

Description copied from interface: java.lang.Runnable

This method will be called by whoever wishes to run your class implementing Runnable. Note that there are no restrictions on what you are allowed to do in the run method, except that you cannot throw a checked exception.

Specified by:

run in interface java.lang.Runnable

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pause

public void pause()

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Pause. No new service is performed until a resume is issued.

Specified by:

pause in interface org.apache.derby.iapi.services.daemon.DaemonService

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resume

public void resume()

Description copied from interface: org.apache.derby.iapi.services.daemon.DaemonService

Resume service after a pause

Specified by:

resume in interface org.apache.derby.iapi.services.daemon.DaemonService

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stop

public void stop()

Finish what we are doing and at the next convenient moment, get rid of the thread and make the daemon object goes away if possible. remember we are calling from another thread

Specified by:

stop in interface org.apache.derby.iapi.services.daemon.DaemonService

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waitUntilQueueIsEmpty

public void waitUntilQueueIsEmpty()

Specified by:

waitUntilQueueIsEmpty in interface org.apache.derby.iapi.services.daemon.DaemonService

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stopRequested

private boolean stopRequested()

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inPause

private boolean inPause()

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wakeUp

protected void wakeUp()

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rest

private boolean rest()

Returns true if awakened by some notification, false if wake up by timer

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work

private void work(boolean urgentOnly)

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yield

private void yield()

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> apache >> derby >> impl >> services >> [ daemon overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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