Class BasicDaemon
- java.lang.Object
-
- org.apache.derby.impl.services.daemon.BasicDaemon
-
- All Implemented Interfaces:
java.lang.Runnable
,DaemonService
public class BasicDaemon extends java.lang.Object implements 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 spurious 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
-
-
Field Summary
Fields Modifier and Type Field Description private boolean
awakened
protected ContextManager
contextMgr
protected ContextService
contextService
private int
earlyWakeupCount
private java.util.List<ServiceRecord>
highPQ
Queues for the work to be done.private boolean
inPause
private long
lastServiceTime
private int
nextService
which subscribed clients to service next?private java.util.List<ServiceRecord>
normPQ
private int
numClients
private static int
OPTIMAL_QUEUE_SIZE
private boolean
running
private boolean
stopped
private boolean
stopRequested
private java.util.Vector<ServiceRecord>
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
Constructors Constructor Description BasicDaemon(ContextService contextService)
make a BasicDaemon
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description void
clear()
Get rid of all queued up Serviceable tasks.boolean
enqueue(Serviceable newClient, boolean serviceNow)
Request a one time service from the Daemon.(package private) static ModuleFactory
getMonitor()
Privileged Monitor lookup.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 timervoid
resume()
Resume service after a pausevoid
run()
protected void
serviceClient(ServiceRecord clientRecord)
void
serviceNow(int clientNumber)
Service this subscription ASAP.private static void
setThreadPriority(ModuleFactory mf, int priority)
Change the priority of the current thread, but only if it was created byModuleFactory.getDaemonThread(java.lang.Runnable, java.lang.String, boolean)
.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(Serviceable newClient, boolean onDemandOnly)
Add a new client that this daemon needs to servicevoid
unsubscribe(int clientNumber)
Removes a client from the list of subscribed clients.void
waitUntilQueueIsEmpty()
protected void
wakeUp()
private void
work(boolean urgentOnly)
private void
yield()
-
-
-
Field Detail
-
numClients
private int numClients
-
OPTIMAL_QUEUE_SIZE
private static final int OPTIMAL_QUEUE_SIZE
- See Also:
- Constant Field Values
-
subscription
private final java.util.Vector<ServiceRecord> subscription
-
contextService
protected final ContextService contextService
-
contextMgr
protected final ContextManager contextMgr
-
highPQ
private final java.util.List<ServiceRecord> highPQ
Queues for the work to be done. These are synchronized by this object.
-
normPQ
private final java.util.List<ServiceRecord> normPQ
-
nextService
private int nextService
which subscribed clients to service next? only accessed by daemon thread
-
awakened
private boolean awakened
-
waiting
private boolean waiting
true if I'm waiting, if this is false then I am running and a notify is not required.
-
inPause
private boolean inPause
-
running
private boolean running
-
stopRequested
private boolean stopRequested
-
stopped
private boolean stopped
-
lastServiceTime
private long lastServiceTime
-
earlyWakeupCount
private int earlyWakeupCount
-
-
Constructor Detail
-
BasicDaemon
public BasicDaemon(ContextService contextService)
make a BasicDaemon
-
-
Method Detail
-
subscribe
public int subscribe(Serviceable newClient, boolean onDemandOnly)
Description copied from interface:DaemonService
Add a new client that this daemon needs to service- Specified by:
subscribe
in interfaceDaemonService
- Parameters:
newClient
- a Serviceable object this daemon will service from time to timeonDemandOnly
- only service this client when it ask for service with a serviceNow request- Returns:
- a client number that uniquely identifies this client (this subscription)
-
unsubscribe
public void unsubscribe(int clientNumber)
Removes a client from the list of subscribed clients. The call does not wait for the daemon to finish the work it is currently performing. Therefore, the client must tolerate that itsperformWork()
method could be invoked even after the call tounsubscribe()
has returned (but not more than once).- Specified by:
unsubscribe
in interfaceDaemonService
- Parameters:
clientNumber
- client identifier
-
serviceNow
public void serviceNow(int clientNumber)
Description copied from interface:DaemonService
Service this subscription ASAP. When this method is called, the subscriber'sperformWork()
method is guaranteed to be invoked at some point in the future. However, there is no guarantee that a subscriber'sperformWork()
is called the same number of times as the subscriber calls this method. More precisely, if a subscriber is waiting for this daemon service to invoke itsperformWork()
method, the daemon service may, but is not required to, ignore requests from that subscriber until theperformWork()
method has been invoked.- Specified by:
serviceNow
in interfaceDaemonService
- Parameters:
clientNumber
- the number that uniquely identifies the client
-
enqueue
public boolean enqueue(Serviceable newClient, boolean serviceNow)
Description copied from interface: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 interfaceDaemonService
- Parameters:
newClient
- the object that needs a one time serviceserviceNow
- if true, this client should be serviced ASAP, as if a serviceNow has been issued. If false, then this client will be serviced with the normal scheduled.- Returns:
- true if the daemon indicates it is being overloaded, false it's happy.
-
clear
public void clear()
Get rid of all queued up Serviceable tasks.- Specified by:
clear
in interfaceDaemonService
-
nextAssignment
protected ServiceRecord nextAssignment(boolean urgent)
-
serviceClient
protected void serviceClient(ServiceRecord clientRecord)
-
run
public void run()
- Specified by:
run
in interfacejava.lang.Runnable
-
pause
public void pause()
Description copied from interface:DaemonService
Pause. No new service is performed until a resume is issued.- Specified by:
pause
in interfaceDaemonService
-
resume
public void resume()
Description copied from interface:DaemonService
Resume service after a pause- Specified by:
resume
in interfaceDaemonService
-
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 interfaceDaemonService
-
waitUntilQueueIsEmpty
public void waitUntilQueueIsEmpty()
- Specified by:
waitUntilQueueIsEmpty
in interfaceDaemonService
-
stopRequested
private boolean stopRequested()
-
inPause
private boolean inPause()
-
wakeUp
protected void wakeUp()
-
rest
private boolean rest()
Returns true if awakened by some notification, false if wake up by timer
-
work
private void work(boolean urgentOnly)
-
yield
private void yield()
-
setThreadPriority
private static void setThreadPriority(ModuleFactory mf, int priority)
Change the priority of the current thread, but only if it was created byModuleFactory.getDaemonThread(java.lang.Runnable, java.lang.String, boolean)
.
-
getMonitor
static ModuleFactory getMonitor()
Privileged Monitor lookup. Must be package private so that user code can't call this entry point.
-
-