de.aristaflow.adept2.util.locking

Class PessimisticObjectLockManager<O,L>

java.lang.Object

de.aristaflow.adept2.util.locking.ObjectLockManager<O,L>

de.aristaflow.adept2.util.locking.PessimisticObjectLockManager<O,L>

Type Parameters:

O - The type of the objects to be locked (locked object type).

L - The type of the objects that lock (lock owning type).

public class PessimisticObjectLockManager<O,L>
extends ObjectLockManager<O,L>

A manager for (pessimistically) locking objects with reentrant locks whereas the locks are itself object specific. By synchronising appropriately on this class, concurrent modifications of the data structures are prevented. This also requires to track the number of waiting lockers.
Pessimistic locking is usually better in environments where locks live long and are held concurrently (for reading).

Author:

Ulrich Kreher

Field Summary

Fields

Modifier and Type	Field and Description
protected java.lang.reflect.Constructor<? extends ReentrantLock<L>>	lockConstr The constructor for instantiating lock implementations.
protected java.util.Map<O,ReentrantLock<L>>	objectLocks A mapping from the locked object to the corresponding locking object.
protected boolean	serviceLogger Whether the constructor of the lock implementation accepts the service logger.
protected ObjectCounting<O>	waitingLockCount Counts the amount of threads that are waiting to lock an object.

Fields inherited from class de.aristaflow.adept2.util.locking.ObjectLockManager

lockCountManager, lockType, logger

Constructor Summary

Constructors

Constructor and Description
PessimisticObjectLockManager(java.lang.Class<? extends LockCountManager<? super L>> lockCountManager, java.lang.Class<? extends ReentrantLock<L>> lock, java.lang.String lockType, java.util.logging.Logger logger) Creates a new ObjectLockManager with the designated lock count manager providing the "equality" for the designated reentrant locks and of the designated type using pessimistic locking.

Method Summary

Modifier and Type	Method and Description
protected void	getLockForObjectReadWriteDirect(boolean writeLock, L lockingObject, O lockedObject, long timeout) Cf. documentation of ObjectLockManager.getLockForObject(boolean, Object, Object, long).
protected ReentrantLock<L>	getObjectLock(O lockedObject) Gets the lock for the designated object.
boolean	hasLock(boolean writeLock, L lockingObject, O lockedObject) Checks whether the designated object is locked for reading or writing by the designated locking object.
boolean	unlockObject(boolean writeLock, L lockingObject, O lockedObject) Unlocks the designated object by the designated locking object.

Methods inherited from class de.aristaflow.adept2.util.locking.ObjectLockManager

getLockForObject, getLockForObject

Methods inherited from class java.lang.Object

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

Field Detail

objectLocks

protected final java.util.Map<O,ReentrantLock<L>> objectLocks

A mapping from the locked object to the corresponding locking object.

waitingLockCount

protected final ObjectCounting<O> waitingLockCount

Counts the amount of threads that are waiting to lock an object. This is needed for to prevent removal of a lock from objectLocks in case threads are waiting for this lock.

lockConstr

protected final java.lang.reflect.Constructor<? extends ReentrantLock<L>> lockConstr

The constructor for instantiating lock implementations.

serviceLogger

protected final boolean serviceLogger

Whether the constructor of the lock implementation accepts the service logger. Otherwise the usual class logger will be used for all locks.

Constructor Detail

PessimisticObjectLockManager

public PessimisticObjectLockManager(java.lang.Class<? extends LockCountManager<? super L>> lockCountManager,
                                    java.lang.Class<? extends ReentrantLock<L>> lock,
                                    java.lang.String lockType,
                                    java.util.logging.Logger logger)
                             throws java.lang.reflect.InvocationTargetException

Creates a new ObjectLockManager with the designated lock count manager providing the "equality" for the designated reentrant locks and of the designated type using pessimistic locking.
This constructor checks whether the designated lock class and the lock count manager class can be instantiated with the appropriate constructors.

Parameters:

lockCountManager - The lock count manager that encapsulates what locking objects are treated as equal when acquiring a lock. The provided class needs an accessible (public) constructor without parameters.

lock - The reentrant lock to be used for locking. The provided class needs an accessible (public) constructor with accepting the designated lockCountManager (of type Class<? extends LockCountManager<? super L>>) and a boolean.

lockType - The type of locks managed by the created object. This is for user information only.

logger - The logger for log messages.

Throws:

java.lang.reflect.InvocationTargetException - If there are problems instantiating the designated lock count manager or the reentrant lock, an InvocationTargetException will be thrown. This prevents problems at runtime when actually retrieving a lock (which requires creating the corresponding objects).

Method Detail

getObjectLock

protected ReentrantLock<L> getObjectLock(O lockedObject)

Description copied from class: ObjectLockManager

Gets the lock for the designated object. This allows subclasses to use their own data structure for lock management.

Specified by:

getObjectLock in class ObjectLockManager<O,L>

Parameters:

lockedObject - The locked object for which to retrieve the corresponding reentrant lock.

Returns:

The reentrant lock for the designated locked object or null in case the designated object is not locked.

getLockForObjectReadWriteDirect

protected void getLockForObjectReadWriteDirect(boolean writeLock,
                                               L lockingObject,
                                               O lockedObject,
                                               long timeout)
                                        throws java.lang.InterruptedException,
                                               java.util.concurrent.TimeoutException

Description copied from class: ObjectLockManager

Cf. documentation of ObjectLockManager.getLockForObject(boolean, Object, Object, long). Implementors can rely on the first boolean to be set appropriately depending on present locks.

Specified by:

getLockForObjectReadWriteDirect in class ObjectLockManager<O,L>

Parameters:

writeLock - Whether to acquire a write lock. This will already be adapted to a write lock if required, that is, requesting a read lock while having the write lock already.

lockingObject - The object locking the designated object.

lockedObject - The object to lock.

timeout - The time to wait for the lock. A timeout <= 0 means to wait forever (or until the lock is granted).

Throws:

java.lang.InterruptedException - If the thread is interrupted while waiting for the lock, an InterruptedException will be thrown.

java.util.concurrent.TimeoutException - If the designated timeout elapsed before the lock can be acquired, a TimeoutException will be thrown.

hasLock

public boolean hasLock(boolean writeLock,
                       L lockingObject,
                       O lockedObject)

Description copied from class: ObjectLockManager

Checks whether the designated object is locked for reading or writing by the designated locking object.

Overrides:

hasLock in class ObjectLockManager<O,L>

Parameters:

writeLock - Whether the locking object is to be checked for having a write lock on the designated locked object.

lockingObject - The object to check for having the lock on the designated object.

lockedObject - The object to check for the lock lock.

Returns:

Whether the designated locking object has the designated lock on the designated locked object.

unlockObject

public boolean unlockObject(boolean writeLock,
                            L lockingObject,
                            O lockedObject)
                     throws LockException

Description copied from class: ObjectLockManager

Unlocks the designated object by the designated locking object. The lock will not be released if it is held several times. If the LockException occurs while trying to unlock, the lock will still be held when returning.

Overrides:

unlockObject in class ObjectLockManager<O,L>

Parameters:

writeLock - Whether to release the write lock.

lockingObject - The object unlocking the designated object.

lockedObject - The object to unlock.

Returns:

Whether a notification has been sent when unlocking. This is the same as ReentrantLock.Lock.unlock(Object) and usually only required by subclasses.

Throws:

LockException - If the locked object has not locked at all or not by the designated locking object, a LockException will be thrown.