org.apache.derby.impl.services.locks
Class LockControl

java.lang.Object
  org.apache.derby.impl.services.locks.LockControl

All Implemented Interfaces:

Control

public class LockControl

extends java.lang.Object

implements Control

A LockControl contains a reference to the item being locked and doubly linked lists for the granted locks and the waiting locks.

MT - Mutable - Container object : single thread required

Field Summary

private Lock	firstGrant This lock control uses an optimistic locking scheme.
private java.util.List	granted
private Lock	lastPossibleSkip
private Lockable	ref
private java.util.List	waiting

Constructor Summary

private	LockControl(LockControl copyFrom)
protected	LockControl(Lock firstLock, Lockable ref)

Method Summary

Lock	addLock(LockSet ls, java.lang.Object compatabilitySpace, java.lang.Object qualifier) Add a lock into this control, granted it if possible.
private void	addWaiter(java.util.List waiting, Lock lockItem, LockSet ls) Add a lock request to a list of waiters.
void	addWaiters(java.util.Dictionary waiters) Add the waiters of this lock into this Dictionary object.
ActiveLock	firstWaiter() Return the first lock in the wait line, null if the line is empty.
Lock	getFirstGrant()
java.util.List	getGranted()
(package private) java.util.List	getGrants() Return a Stack of the held locks (Lock objects) on this Lockable.
Lock	getLock(java.lang.Object compatabilitySpace, java.lang.Object qualifier) Find a granted lock matching this space and qualifier
Lockable	getLockable() Return the lockable object controlled by me.
LockControl	getLockControl()
(package private) ActiveLock	getNextWaiter(ActiveLock item, boolean remove, LockSet ls) Get the next waiting lock (if any).
java.util.List	getWaiting()
protected void	giveUpWait(java.lang.Object item, LockSet ls) Give up waiting up on a lock
(package private) void	grant(Lock lockItem) Grant this lock.
boolean	isEmpty()
boolean	isGrantable(boolean noWaitersBeforeMe, java.lang.Object compatabilitySpace, java.lang.Object qualifier) This routine can be called to see if a lock currently on the wait list could be granted.
protected boolean	isUnlocked()
private java.lang.Object	popFrontWaiter(java.util.List waiting, LockSet ls) Remove and return the first lock request from a list of waiters.
private java.lang.Object	removeWaiter(java.util.List waiting, int index, LockSet ls) Remove and return the lock request at the given index from a list of waiters.
private int	removeWaiter(java.util.List waiting, java.lang.Object item, LockSet ls) Remove and return the given lock request from a list of waiters.
Control	shallowClone() make a shallow clone of myself
boolean	unlock(Latch lockInGroup, int unlockCount)

Methods inherited from class java.lang.Object

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

Field Detail

ref

private final Lockable ref

firstGrant

private Lock firstGrant

This lock control uses an optimistic locking scheme. When the first lock on an object is granted it simply sets firstGrant to be that object, removing the need to allocate a list if no other locks are granted before the first lock is release. If a second lock is granted then a list is allocated and the firstGrant lock is moved into the list. Once a list has been created it is always used.

granted

private java.util.List granted

waiting

private java.util.List waiting

lastPossibleSkip

private Lock lastPossibleSkip

Constructor Detail

LockControl

protected LockControl(Lock firstLock,
                      Lockable ref)

LockControl

private LockControl(LockControl copyFrom)

Method Detail

getLockControl

public LockControl getLockControl()

Specified by:

getLockControl in interface Control

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Control

grant

void grant(Lock lockItem)

Grant this lock.

unlock

public boolean unlock(Latch lockInGroup,
                      int unlockCount)

Specified by:

unlock in interface Control

isGrantable

public boolean isGrantable(boolean noWaitersBeforeMe,
                           java.lang.Object compatabilitySpace,
                           java.lang.Object qualifier)

This routine can be called to see if a lock currently on the wait list could be granted. If this lock has waiters ahead of it then we do not jump over the waiter(s) even if we can be granted. This avoids the first waiter being starved out.

Specified by:

isGrantable in interface Control

addLock

public Lock addLock(LockSet ls,
                    java.lang.Object compatabilitySpace,
                    java.lang.Object qualifier)

Add a lock into this control, granted it if possible. This can be entered in several states.

The Lockable is locked (granted queue not empty), and there are no waiters (waiting queue is empty)

The Lockable is locked and there are waiters

The Lockable is locked and there are waiters and the first is potentially granted

The Lockable is unlocked and there are waiters and the first is potentially granted. Logically the item is still locked, it's just that the lock has just been released and the first waker has not woken up yet. This call is never entered when the object is unlocked and there are no waiters. 1) The Lockable has just been unlocked,

isUnlocked

protected boolean isUnlocked()

firstWaiter

public ActiveLock firstWaiter()

Return the first lock in the wait line, null if the line is empty.

Specified by:

firstWaiter in interface Control

getNextWaiter

ActiveLock getNextWaiter(ActiveLock item,
                         boolean remove,
                         LockSet ls)

Get the next waiting lock (if any).

getLockable

public Lockable getLockable()

Return the lockable object controlled by me.

Specified by:

getLockable in interface Control

getFirstGrant

public Lock getFirstGrant()

Specified by:

getFirstGrant in interface Control

getGranted

public java.util.List getGranted()

Specified by:

getGranted in interface Control

getWaiting

public java.util.List getWaiting()

Specified by:

getWaiting in interface Control

giveUpWait

protected void giveUpWait(java.lang.Object item,
                          LockSet ls)

Give up waiting up on a lock

addWaiters

public void addWaiters(java.util.Dictionary waiters)

Add the waiters of this lock into this Dictionary object.
Each waiting thread gets two entries in the hashtable

1. key=compatibility space - value=ActiveLock
2. key=ActiveLock - value={LockControl for first waiter|ActiveLock of previosue waiter}

Specified by:

addWaiters in interface Control

getGrants

java.util.List getGrants()

Return a Stack of the held locks (Lock objects) on this Lockable.

getLock

public final Lock getLock(java.lang.Object compatabilitySpace,
                          java.lang.Object qualifier)

Find a granted lock matching this space and qualifier

Specified by:

getLock in interface Control

shallowClone

public Control shallowClone()

make a shallow clone of myself

Specified by:

shallowClone in interface Control

addWaiter

private void addWaiter(java.util.List waiting,
                       Lock lockItem,
                       LockSet ls)

Add a lock request to a list of waiters.

Parameters:

waiting - The list of waiters to add to

lockItem - The lock request

ls - The LockSet

popFrontWaiter

private java.lang.Object popFrontWaiter(java.util.List waiting,
                                        LockSet ls)

Remove and return the first lock request from a list of waiters.

Parameters:

waiting - The list of waiters to pop from

ls - The LockSet

Returns:

The removed lock request

removeWaiter

private java.lang.Object removeWaiter(java.util.List waiting,
                                      int index,
                                      LockSet ls)

Remove and return the lock request at the given index from a list of waiters.

Parameters:

waiting - The list of waiters to pop from

index - The index at which to remove the lock request

ls - The LockSet

Returns:

The removed lock request

removeWaiter

private int removeWaiter(java.util.List waiting,
                         java.lang.Object item,
                         LockSet ls)

Remove and return the given lock request from a list of waiters.

Parameters:

waiting - The list of waiters to pop from

item - The item to remove

ls - The LockSet

Returns:

The number of items removed