org.apache.hadoop.hbase

Class ChoreService

java.lang.Object

org.apache.hadoop.hbase.ChoreService

@InterfaceAudience.Private
public class ChoreService
extends Object

ChoreService is a service that can be used to schedule instances of ScheduledChore to run periodically while sharing threads. The ChoreService is backed by a ScheduledThreadPoolExecutor whose core pool size changes dynamically depending on the number of ScheduledChore scheduled. All of the threads in the core thread pool of the underlying ScheduledThreadPoolExecutor are set to be daemon threads.

The ChoreService provides the ability to schedule, cancel, and trigger instances of ScheduledChore. The ChoreService also provides the ability to check on the status of scheduled chores. The number of threads used by the ChoreService changes based on the scheduling load and whether or not the scheduled chores are executing on time. As more chores are scheduled, there may be a need to increase the number of threads if it is noticed that chores are no longer meeting their scheduled start times. On the other hand, as chores are cancelled, an attempt is made to reduce the number of running threads to see if chores can still meet their start times with a smaller thread pool.

When finished with a ChoreService it is good practice to call shutdown(). Calling this method ensures that all scheduled chores are cancelled and cleaned up properly.

Field Summary

Fields

Modifier and Type	Field and Description
static int	MIN_CORE_POOL_SIZE The minimum number of threads in the core pool of the underlying ScheduledThreadPoolExecutor

Constructor Summary

Constructors

Constructor and Description
ChoreService(String coreThreadPoolPrefix)
ChoreService(String coreThreadPoolPrefix, int corePoolSize)

Method Summary

Modifier and Type	Method and Description
void	cancelChore(ScheduledChore chore) Cancel any ongoing schedules that this chore has with the implementer of this interface.
void	cancelChore(ScheduledChore chore, boolean mayInterruptIfRunning)
static ChoreService	getInstance(String coreThreadPoolPrefix)
boolean	isChoreScheduled(ScheduledChore chore)
boolean	isShutdown()
boolean	isTerminated()
void	onChoreMissedStartTime(ScheduledChore chore) A callback that tells the implementer of this interface that one of the scheduled chores is missing its start time.
boolean	scheduleChore(ScheduledChore chore)
void	shutdown() shutdown the service.
boolean	triggerNow(ScheduledChore chore) This method tries to execute the chore immediately.

Methods inherited from class java.lang.Object

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

Field Detail

MIN_CORE_POOL_SIZE

public static final int MIN_CORE_POOL_SIZE

The minimum number of threads in the core pool of the underlying ScheduledThreadPoolExecutor

See Also:

Constant Field Values

Constructor Detail

ChoreService

public ChoreService(String coreThreadPoolPrefix)

Parameters:

coreThreadPoolPrefix - Prefix that will be applied to the Thread name of all threads spawned by this service

ChoreService

public ChoreService(String coreThreadPoolPrefix,
                    int corePoolSize)

Parameters:

coreThreadPoolPrefix - Prefix that will be applied to the Thread name of all threads spawned by this service

corePoolSize - The initial size to set the core pool of the ScheduledThreadPoolExecutor to during initialization. The default size is 1, but specifying a larger size may be beneficial if you know that 1 thread will not be enough.

Method Detail

getInstance

public static ChoreService getInstance(String coreThreadPoolPrefix)

Parameters:

coreThreadPoolPrefix - Prefix that will be applied to the Thread name of all threads spawned by this service

scheduleChore

public boolean scheduleChore(ScheduledChore chore)

Parameters:

chore - Chore to be scheduled. If the chore is already scheduled with another ChoreService instance, that schedule will be cancelled (i.e. a Chore can only ever be scheduled with a single ChoreService instance).

Returns:

true when the chore was successfully scheduled. false when the scheduling failed (typically occurs when a chore is scheduled during shutdown of service)

cancelChore

public void cancelChore(ScheduledChore chore)

Cancel any ongoing schedules that this chore has with the implementer of this interface.

cancelChore

public void cancelChore(ScheduledChore chore,
                        boolean mayInterruptIfRunning)

isChoreScheduled

public boolean isChoreScheduled(ScheduledChore chore)

Returns:

true when the chore is scheduled with the implementer of this interface

triggerNow

public boolean triggerNow(ScheduledChore chore)

This method tries to execute the chore immediately. If the chore is executing at the time of this call, the chore will begin another execution as soon as the current execution finishes

If the chore is not scheduled with a ChoreService, this call will fail.

Returns:

false when the chore could not be triggered immediately

onChoreMissedStartTime

public void onChoreMissedStartTime(ScheduledChore chore)

A callback that tells the implementer of this interface that one of the scheduled chores is missing its start time. The implication of a chore missing its start time is that the service's current means of scheduling may not be sufficient to handle the number of ongoing chores (the other explanation is that the chore's execution time is greater than its scheduled period). The service should try to increase its concurrency when this callback is received.

Parameters:

chore - The chore that missed its start time

shutdown

public void shutdown()

shutdown the service. Any chores that are scheduled for execution will be cancelled. Any chores in the middle of execution will be interrupted and shutdown. This service will be unusable after this method has been called (i.e. future scheduling attempts will fail).

isShutdown

public boolean isShutdown()

Returns:

true when the service is shutdown and thus cannot be used anymore

isTerminated

public boolean isTerminated()

Returns:

true when the service is shutdown and all threads have terminated