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

java.lang.Object
  org.apache.derby.impl.services.locks.Lock
      org.apache.derby.impl.services.locks.ActiveLock

All Implemented Interfaces:

Control, org.apache.derby.iapi.services.locks.Latch

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public final class ActiveLock

extends Lock

A Lock represents a granted or waiting lock request.
MT - Mutable - Immutable identity : Thread Aware

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Field Summary
protected  boolean	canSkip           If true then this lock can be granted even if it is not the first lock request on the wait queue.
(package private)  boolean	potentiallyGranted           Set to true if the Lock potentially could be granted.
(package private)  byte	wakeUpNow           Set to true if the object waiting on this thread should wake up, MT - mutable - java synchronized(this)

 

Fields inherited from class org.apache.derby.impl.services.locks.Lock

count

 

Constructor Summary
protected	ActiveLock(java.lang.Object space, org.apache.derby.iapi.services.locks.Lockable ref, java.lang.Object qualifier)           Initialize the lock, should be seen as part of the constructor.

 

Method Summary
protected  void	clearPotentiallyGranted()           Clear the potentially granted flag.
protected  boolean	setPotentiallyGranted()           Set the potentially granted flag, returns true if the flag changed its state.
protected  byte	waitForGrant(int timeout)           Wait for a lock to be granted, returns when the lock is granted.
protected  void	wakeUp(byte why)           Wake up anyone sleeping on this lock.

 

Methods inherited from class org.apache.derby.impl.services.locks.Lock

addWaiters, copy, equals, firstWaiter, getCompatabilitySpace, getCount, getFirstGrant, getGranted, getLock, getLockable, getLockControl, getQualifier, getWaiting, grant, hashCode, isEmpty, isGrantable, shallowClone, unlock, unlock

 

Methods inherited from class java.lang.Object

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

 

Field Detail

wakeUpNow

byte wakeUpNow

Set to true if the object waiting on this thread should wake up, MT - mutable - java synchronized(this)

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potentiallyGranted

boolean potentiallyGranted

Set to true if the Lock potentially could be granted. MT - mutable - single thread required

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canSkip

protected boolean canSkip

If true then this lock can be granted even if it is not the first lock request on the wait queue. This can occur if the compatability space already holds a lock on the object.

Constructor Detail

ActiveLock

protected ActiveLock(java.lang.Object space,
                     org.apache.derby.iapi.services.locks.Lockable ref,
                     java.lang.Object qualifier)

Initialize the lock, should be seen as part of the constructor. A future version of this class may become mutable - mutable identity. MT - single thread required

Method Detail

setPotentiallyGranted

protected boolean setPotentiallyGranted()

Set the potentially granted flag, returns true if the flag changed its state. MT - single thread required

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clearPotentiallyGranted

protected void clearPotentiallyGranted()

Clear the potentially granted flag. MT - single thread required

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waitForGrant

protected byte waitForGrant(int timeout)
                     throws org.apache.derby.iapi.error.StandardException

Wait for a lock to be granted, returns when the lock is granted.

The sleep wakeup scheme depends on the two booleans wakeUpNow & potentiallyGranted. MT - Single thread required - and assumed to be the thread requesting the lock.

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wakeUp

protected void wakeUp(byte why)

Wake up anyone sleeping on this lock. MT - Thread Safe

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