public abstract class SingletonSchedulableService extends SchedulableService
SingletonSchedulableService is an appropriate choice for any scheduled service that must run exactly once for a given set of input data. Periodic report generation is one example: each report should be generated once and only once, but report generation should not fail if a single Dynamo server is down. Processing scheduled orders in a commerce application is another example: orders must be processed regardless of the status of any particular Dynamo server, but it is vital that each order be placed exactly once.
SingletonSchedulableService relies on a lock manager to ensure exclusive
operation. Each service is configured with a reference to a client lock
manager and a lock name. The client lock managers on all Dynamo hosts
are configured to refer to the same server lock manager. When a
SingletonSchedulableService's performScheduledTask method is
called, it attempts to obtain a global write lock from the lock manager.
If the lock is obtained successfully, the service calls its own
doScheduledTask method. If the lock is not obtained, the
service assumes that some other instance of the service is currently
running and waits until the next time the scheduler calls it.
Unlike subclasses of SchedulableService, which implement application
specific functionality by implementing the
performScheduledTask method, subclasses of
SingletonSchedulableService implement functionality by implementing
doScheduledTask.
SchedulableService| Modifier and Type | Field and Description |
|---|---|
static java.lang.String |
CLASS_VERSION |
mJobIdSERVICE_INFO_KEYDEFAULT_LOG_TRACE_STATUSDEFAULT_LOG_DEBUG_STATUS, DEFAULT_LOG_ERROR_STATUS, DEFAULT_LOG_INFO_STATUS, DEFAULT_LOG_WARNING_STATUS| Constructor and Description |
|---|
SingletonSchedulableService() |
| Modifier and Type | Method and Description |
|---|---|
protected boolean |
acquireLock()
The method will attempt to acqure an exclusive write lock.
|
abstract void |
doScheduledTask(Scheduler pScheduler,
ScheduledJob pJob)
Perform the scheduled task for this service.
|
ClientLockManager |
getClientLockManager()
Get the ClientLockManager used to ensure that only one
instance of the service is running at any given time.
|
java.lang.String |
getLockName()
Get the name of the global write lock that identifies this service.
|
long |
getLockTimeOut()
Get the maximum time we wait for a lock, in milliseconds.
|
void |
performScheduledTask(Scheduler pScheduler,
ScheduledJob pJob)
The method will be called by the scheduler according to its schedule.
|
protected void |
releaseLock()
This method will release the lock, using the
ClientLockManager |
void |
setClientLockManager(ClientLockManager pClientLockManager)
Set the ClientLockManager used to ensure that only one
instance of the service is running at any given time.
|
void |
setLockName(java.lang.String pLockName)
Set the name of the global write lock that identifies this service.
|
void |
setLockTimeOut(long pLockTimeOut)
Set the maximum time we wait for a lock, in milliseconds.
|
doStartService, doStopService, getJobDescription, getJobId, getJobName, getSchedule, getScheduler, getThreadMethod, getThreadMethodString, isTransactional, setJobDescription, setJobName, setSchedule, setScheduler, setThreadMethod, setThreadMethodString, setTransactional, startScheduledJob, stopScheduledJobaddLogListener, createAdminServlet, getAbsoluteName, getAdminServlet, getAdminServletOutputStreamEncoding, getLoggingForVlogging, getLogListenerCount, getLogListeners, getName, getNameContext, getNucleus, getRoot, getServiceConfiguration, getServiceInfo, isAdminServletUseServletOutputStream, isLoggingDebug, isLoggingError, isLoggingInfo, isLoggingTrace, isLoggingWarning, isRunning, logDebug, logDebug, logDebug, logError, logError, logError, logInfo, logInfo, logInfo, logTrace, logTrace, logTrace, logWarning, logWarning, logWarning, nameContextElementBound, nameContextElementUnbound, removeLogListener, reResolveThis, resolveName, resolveName, resolveName, resolveName, sendLogEvent, setAdminServletOutputStreamEncoding, setAdminServletUseServletOutputStream, setLoggingDebug, setLoggingError, setLoggingInfo, setLoggingTrace, setLoggingWarning, setNucleus, setServiceInfo, startService, stopServicevlogDebug, vlogDebug, vlogDebug, vlogDebug, vlogDebugTrace, vlogError, vlogError, vlogError, vlogError, vlogInfo, vlogInfo, vlogInfo, vlogInfo, vlogTrace, vlogTrace, vlogTrace, vlogTrace, vlogWarning, vlogWarning, vlogWarning, vlogWarningpublic void setClientLockManager(ClientLockManager pClientLockManager)
public ClientLockManager getClientLockManager()
public void setLockName(java.lang.String pLockName)
public java.lang.String getLockName()
public void setLockTimeOut(long pLockTimeOut)
public long getLockTimeOut()
protected boolean acquireLock()
lockName from the
client lock manager specified by ClientLockManager.
If the lock is obtained this method return true; If the lock is not obtained, or is not a global lock, the method returns false.
Note: If the client lock manager is configured with its
useLockServer property set to false it means that
global locking is not enabled for that lock manager. In that case,
acquireLock will accept a local lock instead.
protected void releaseLock()
ClientLockManagerpublic void performScheduledTask(Scheduler pScheduler, ScheduledJob pJob)
acquireLock
If the lock is obtained this method will call
doScheduledTask. If the lock is not obtained the call to
doScheduledTask will be skipped.
In either case, the lock will be released before this method returns
by calling releaseLock
performScheduledTask in interface SchedulableperformScheduledTask in class SchedulableServicepScheduler - the scheduler managing this jobpJob - the scheduled job associated with this servicepublic abstract void doScheduledTask(Scheduler pScheduler, ScheduledJob pJob)