org.apache.hadoop.hbase.procedure2

Class LockAndQueue

java.lang.Object

org.apache.hadoop.hbase.procedure2.LockAndQueue

All Implemented Interfaces:

LockStatus

@InterfaceAudience.Private
public class LockAndQueue
extends Object
implements LockStatus

Locking for mutual exclusion between procedures. Used only by procedure framework internally. LockAndQueue has two purposes:

1. Acquire/release exclusive/shared locks.
2. Maintains a list of procedures waiting on this lock. LockAndQueue extends ProcedureDeque class. Blocked Procedures are added to our super Deque. Using inheritance over composition to keep the Deque of waiting Procedures is unusual, but we do it this way because in certain cases, there will be millions of regions. This layout uses less memory.

NOT thread-safe. Needs external concurrency control: e.g. uses in MasterProcedureScheduler are guarded by schedLock().
There is no need of 'volatile' keyword for member variables because of memory synchronization guarantees of locks (see 'Memory Synchronization', http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/Lock.html)
We do not implement Lock interface because we need exclusive and shared locking, and also because try-lock functions require procedure id.
We do not use ReentrantReadWriteLock directly because of its high memory overhead.

Field Summary

Fields

Modifier and Type	Field and Description
private Procedure<?>	exclusiveLockOwnerProcedure
private Function<Long,Procedure<?>>	procedureRetriever
private ProcedureDeque	queue
private int	sharedLock

Constructor Summary

Constructors

Constructor and Description
LockAndQueue(Function<Long,Procedure<?>> procedureRetriever)

Method Summary

Modifier and Type	Method and Description
void	addLast(Procedure<?> proc)
Stream<Procedure>	filterWaitingQueue(Predicate<Procedure> predicate)
Procedure<?>	getExclusiveLockOwnerProcedure() Get the procedure which holds the exclusive lock.
int	getSharedLockCount() Get the number of procedures which hold the shared lock.
boolean	hasExclusiveLock() Whether the exclusive lock has been held.
boolean	hasLockAccess(Procedure<?> proc) Return true if the procedure itself holds the exclusive lock, or any ancestors of the give procedure hold the exclusive lock.
boolean	isWaitingQueueEmpty()
boolean	releaseExclusiveLock(Procedure<?> proc)
boolean	releaseSharedLock()
Procedure<?>	removeFirst()
String	toString()
boolean	tryExclusiveLock(Procedure<?> proc)
boolean	trySharedLock(Procedure<?> proc)
int	wakeWaitingProcedures(ProcedureScheduler scheduler)

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.hbase.procedure2.LockStatus

getExclusiveLockProcIdOwner, isLocked

Field Detail

procedureRetriever

private final Function<Long,Procedure<?>> procedureRetriever

queue

private final ProcedureDeque queue

exclusiveLockOwnerProcedure

private Procedure<?> exclusiveLockOwnerProcedure

sharedLock

private int sharedLock

Constructor Detail

LockAndQueue

public LockAndQueue(Function<Long,Procedure<?>> procedureRetriever)

Method Detail

hasExclusiveLock

public boolean hasExclusiveLock()

Description copied from interface: LockStatus

Whether the exclusive lock has been held.

Specified by:

hasExclusiveLock in interface LockStatus

hasLockAccess

public boolean hasLockAccess(Procedure<?> proc)

Description copied from interface: LockStatus

Return true if the procedure itself holds the exclusive lock, or any ancestors of the give procedure hold the exclusive lock.

Specified by:

hasLockAccess in interface LockStatus

getExclusiveLockOwnerProcedure

public Procedure<?> getExclusiveLockOwnerProcedure()

Description copied from interface: LockStatus

Get the procedure which holds the exclusive lock.

Specified by:

getExclusiveLockOwnerProcedure in interface LockStatus

getSharedLockCount

public int getSharedLockCount()

Description copied from interface: LockStatus

Get the number of procedures which hold the shared lock.

Specified by:

getSharedLockCount in interface LockStatus

trySharedLock

public boolean trySharedLock(Procedure<?> proc)

Returns:

whether we have succesfully acquired the shared lock.

releaseSharedLock

public boolean releaseSharedLock()

Returns:

whether we should wake the procedures waiting on the lock here.

tryExclusiveLock

public boolean tryExclusiveLock(Procedure<?> proc)

releaseExclusiveLock

public boolean releaseExclusiveLock(Procedure<?> proc)

Returns:

whether we should wake the procedures waiting on the lock here.

isWaitingQueueEmpty

public boolean isWaitingQueueEmpty()

removeFirst

public Procedure<?> removeFirst()

addLast

public void addLast(Procedure<?> proc)

wakeWaitingProcedures

public int wakeWaitingProcedures(ProcedureScheduler scheduler)

filterWaitingQueue

public Stream<Procedure> filterWaitingQueue(Predicate<Procedure> predicate)

toString

public String toString()

Overrides:

toString in class Object