| org.apache.derby.iapi.services.locks.Lockable
All known Subclasses: org.apache.derby.iapi.store.raw.ContainerKey, org.apache.derby.impl.store.raw.data.BasePage, org.apache.derby.impl.store.raw.data.BaseContainer, org.apache.derbyTesting.unitTests.services.T_L2, org.apache.derbyTesting.unitTests.services.T_L1, org.apache.derby.iapi.services.locks.ShExLockable,
| Lockable | | public interface Lockable (Code) | | Any object that needs to be locked must implement Lockable.
This allows a generic lock manager that can have locking policies
defined on a per-object basis.
A request to lock the object takes a qualifier, this qualifier may be
used the object to implement a complex locking policy, e.g. traditional
database shared, update and exclusive locks.
The lock manager uses this ordered protocol to determine if a lock request on a
Lockable L with qualifier Q1 in compatiblity space
CS1 can be granted:
- If no locks are held on L in any compatability space then the
request is granted.
- If L.requestCompatible(Q1) returns true then the lock is granted.
- Otherwise the request is granted if the following expression evaluates
to true for every other lock { CSn, Qn} held on L
If the request is granted then a call is made to L.lockEvent(CS1, Q1) .
When the lock is released a call is made to L.unlockEvent(CS1, Q1) .
The lock manager uses equals() and hashCode() to identify unique Lockables.
If the class implementing Lockable requires that each instance of class
correspond to a different locked object then the equals() method must test
equality via the reference equality test (==), this is the default behaviour
for equality.
If the class implementing Lockable require that each instance of the class
that has the same value (as defined by the class) corresponds to a locked
object then its equals() method must reflect that, e.g. by testing equality
of its fields. In this case the first Lockable to be locked will be kept
by lock manager as the key for the lock. Thus even after the first caller
unlocks the obejct, its reference will still be kept by the lock manager.
Thus Lockable's that per value equality must be designed so that they
are never re-used for different lockable concepts.
In either case the equals() method must accept a reference to an object of
a different type.
As per standard hashtable rules the value returned by hashCode() must be in sync
with the equals() method.
MT - Mutable - : single thread required, synchronization is provided by the lock manager.
If the class implementing Lockable uses value equality then it must have an immutable identity.
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| Method Summary | |
| public boolean | lockAttributes(int flag, Hashtable attributes)
If this lockable object wants to participate in a diagnostic virtual
lock table, then put any relavent attributes of this lock into the
attributes list (the attribute must be an immutable object). | | public void | lockEvent(Latch lockInfo)
Note the fact the object is locked. | | public boolean | lockerAlwaysCompatible()
Returns true if any lock request on a Lockable L in a compatibility space CS1 is compatible
with any other lock held on L in CS1. | | public boolean | requestCompatible(Object requestedQualifier, Object grantedQualifier)
Return true if the requested qualifier is compatible with the already granted
qualifier. | | public void | unlockEvent(Latch lockInfo)
Note that the object has been unlocked
Must only be called by the lock manager. |
| lockAttributes | | public boolean lockAttributes(int flag, Hashtable attributes)(Code) | | If this lockable object wants to participate in a diagnostic virtual
lock table, then put any relavent attributes of this lock into the
attributes list (the attribute must be an immutable object). The list
of attributes of interest to the virtual lock table can be found in
VirtualLockTable. The toString method will be called by the VirtualTable
on the attribute value for display.
Parameters:
flag - use the bits in this int to decide if the user isinterested in this kind of lockable object. The bits are defined inVirtualLockTable. For instance, the user may only askfor TABLE_AND_ROWLOCK and if this is not a table or row lock, thendon't paritipate.
Parameters:
attributes - if this decides to participate, put all relaventattributes into the Hashtable. The complete list of interestingattributes is listed in VirtualLockTable.The following attributes must be present for all participatinglockables:VirtualLockTable.LOCKNAME,VirtualLockTable.LOCKTYPE,either VirtualLockTable.CONTAINERID or VirtualLockTable.CONGLOMID, MT - this routine must be MP safe, caller will not be single threadingthe lock manager. true if this object has diagnostic information to add to thevirtual lock table. If this object either does not want to participatein the diagnostic virtual lock table or none of the attributesrequested are attributes of this lock, returns false.
See Also: VirtualLockTable |
| lockEvent | | public void lockEvent(Latch lockInfo)(Code) | | Note the fact the object is locked. Performs required actions
to ensure that unlockEvent() work correctly.
This method does not actually perform any locking of the
object, the locking mechanism is provided by the lock manager.
If the class supports multiple lockers of the object then this method
will be called once per locker, each with their own qualifier.
Must only be called by the lock manager. Synchronization will be handled
by the lock manager.
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| lockerAlwaysCompatible | | public boolean lockerAlwaysCompatible()(Code) | | Returns true if any lock request on a Lockable L in a compatibility space CS1 is compatible
with any other lock held on L in CS1.
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| requestCompatible | | public boolean requestCompatible(Object requestedQualifier, Object grantedQualifier)(Code) | | Return true if the requested qualifier is compatible with the already granted
qualifier.
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| unlockEvent | | public void unlockEvent(Latch lockInfo)(Code) | | Note that the object has been unlocked
Must only be called by the lock manager. Synchronization will be handled
by the lock manager.
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