arlut.csd.ganymede.server

Class DBLockSync

java.lang.Object

arlut.csd.ganymede.server.DBLockSync

public final class DBLockSync
extends java.lang.Object

This class acts to provide a singleton object for interlock coordination. All global data required for coordinating DBLock lock activity is stored in the singleton object.

Note that much code in the various DBLock subclasses, and in the rest of the Ganymede server, establishes external synchronization on the DBLockSync object referenced in DBStore.lockSync, so certain methods in this class which do not appear synchronized may in fact be dependent on external synchronization.

Field Summary

Fields

Modifier and Type	Field and Description
private java.util.Hashtable	lockHash Identifier keys for current DBLocks.
private int	locksHeld A count of how many DBLocks are established on DBObjectBases in this DBStore.
private int	locksWaiting A count of how many DBLocks are waiting to be established on DBObjectBases in this DBStore.

Constructor Summary

Constructors

Constructor and Description
DBLockSync()

Method Summary

Methods

Modifier and Type	Method and Description
boolean	claimLockKey(java.lang.Object key, DBLock lock) This method associates a DBLock with the given key, making sure that there is no conflicting lock request for the key
void	decLockCount() Decrements the count of held locks for the admin consoles.
void	decLocksWaitingCount() Decrements the count of locks waiting to be established.
int	getLockCount() Returns the number of locks presently held in the database.
DBLock	getLockHeld(java.lang.Object key) This method returns a DBLock associated with the given key, if any.
int	getLocksWaitingCount() Returns the number of locks currently waiting to be established.
java.util.Vector	getReadLockVector(java.lang.Object key) This method returns a Vector of DBReadLock objects associated with key, if any.
void	incLockCount() Increments the count of held locks for the admin consoles.
void	incLocksWaitingCount() Increments the count of locks waiting to be established.
void	resetLockHash(int count) This method causes the DBLockSync object's lock owner hashtable to be reset.
void	unclaimLockKey(java.lang.Object key, DBLock lock) This method disassociates a DBLock from the given key If the key was not previously claimed for the given lock, an IllegalStateException will be thrown.

Methods inherited from class java.lang.Object

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

Field Detail

lockHash

private java.util.Hashtable lockHash

Identifier keys for current DBLocks.

This hash is used by the establish() method in various DBLock subclasses to guarantee that only one lock will established by a client at a time, to prevent any possibility of DBLock deadlock.

The values in this hash may either be scalar DBLock objects, or in the case of readers (where it is permissible for a single client to have several distinct reader locks), a Vector of DBLocks.

locksHeld

private int locksHeld

A count of how many DBLocks are established on DBObjectBases in this DBStore.

locksWaiting

private int locksWaiting

A count of how many DBLocks are waiting to be established on DBObjectBases in this DBStore.

Constructor Detail

DBLockSync

public DBLockSync()

Method Detail

resetLockHash

public void resetLockHash(int count)

This method causes the DBLockSync object's lock owner hashtable to be reset. If count is not zero, that value will be used to set the initial capacity for the hashtable.

claimLockKey

public boolean claimLockKey(java.lang.Object key,
                   DBLock lock)

This method associates a DBLock with the given key, making sure that there is no conflicting lock request for the key

Returns:

True if the lock could be associated with key, False if there was a pre-existing conflicting association.

unclaimLockKey

public void unclaimLockKey(java.lang.Object key,
                  DBLock lock)

This method disassociates a DBLock from the given key

If the key was not previously claimed for the given lock, an IllegalStateException will be thrown.

getReadLockVector

public java.util.Vector getReadLockVector(java.lang.Object key)

This method returns a Vector of DBReadLock objects associated with key, if any. If there is no DBReadLock vector associated with the key, an IllegalStateException will be thrown.

The Vector returned is part of DBLockSync's internal data structures, and should only be browsed in a block synchronized on this DBLockSync object.

The Vector returned should not be modified by external code.

getLockHeld

public DBLock getLockHeld(java.lang.Object key)

This method returns a DBLock associated with the given key, if any.

This method will only ever return a DBWriteLock or a DBDumpLock. If the key is associated with a Vector of DBReadLocks, null will be returned.

incLocksWaitingCount

public void incLocksWaitingCount()

Increments the count of locks waiting to be established.

decLocksWaitingCount

public void decLocksWaitingCount()

Decrements the count of locks waiting to be established.

incLockCount

public void incLockCount()

Increments the count of held locks for the admin consoles.

decLockCount

public void decLockCount()

Decrements the count of held locks for the admin consoles.

getLocksWaitingCount

public int getLocksWaitingCount()

Returns the number of locks currently waiting to be established.

getLockCount

public int getLockCount()

Returns the number of locks presently held in the database.