Cacheable

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org.apache.derby.iapi.services.cache
Interface Cacheable

All Known Subinterfaces:: SizedCacheable

public interface Cacheable

Any object that implements this interface can be cached using the services of the CacheManager/CacheFactory. In addition to implementing this interface the class must be public and it must have a public no-arg constructor. This is because the cache manager will construct objects itself and then set their identity by calling the setIdentity method.

A Cacheable object has five states:

No identity - The object is only accessable by the cache manager
Identity, clean, unkept - The object has an identity, is clean but is only accessable by the cache manager
Identity, clean, kept - The object has an identity, is clean, and is in use by one or more threads
Identity, kept, dirty - The object has an identity, is dirty, and is in use by one or more threads
Identity, unkept, dirty - The object has an identity, is dirty but is only accessable by the cache manager

While the object is kept it is guaranteed not to change identity. While it is unkept no-one outside of the cache manager can have a reference to the object. The cache manager returns kept objects and they return to the unkept state when all the current users of the object have released it.
It is required that the object can only move into a dirty state while it is kept.
MT - Mutable : thread aware - Calls to Cacheable method must only be made by the cache manager or the object itself.

Method Summary

void clean(boolean forRemove)
          Clean the object.

void clearIdentity()
          Put the object into the No Identity state.

Cacheable createIdentity(java.lang.Object key, java.lang.Object createParameter)
          Create a new item.

java.lang.Object getIdentity()
          Get the identity of this object.

boolean isDirty()
          Returns true of the object is dirty.

Cacheable setIdentity(java.lang.Object key)
          Set the identity of the object.

Method Detail

setIdentity

public Cacheable setIdentity(java.lang.Object key)
                      throws org.apache.derby.iapi.error.StandardException

Set the identity of the object.

Set the identity of the object to represent an item that already exists, e.g. an existing container. The object will be in the No Identity state, ie. it will have just been created or clearIdentity() was just called.
The object must copy the information out of key, not just store a reference to key. After this call the expression getIdentity().equals(key) must return true.
If the class of the object needs to change (e.g. to support a different format) then the object should create a new object, call its initParameter() with the parameters the original object was called with, set its identity and return a reference to it. The cache manager will discard the reference to the old object.
If an exception is thrown the object must be left in the no-identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.

createIdentity

public Cacheable createIdentity(java.lang.Object key,
                                java.lang.Object createParameter)
                         throws org.apache.derby.iapi.error.StandardException

Create a new item.

Create a new item and set the identity of the object to represent it. The object will be in the No Identity state, ie. it will have just been created or clearIdentity() was just called.
The object must copy the information out of key, not just store a reference to key if the key is not immutable. After this call the expression getIdentity().equals(key) must return true.

If the class of the object needs to change (e.g. to support a different format) then the object should create a new object, call its initParameter() with the parameters the original object was called with, set its identity and return a reference to it. The cache manager will discard the reference to the old object.
If an exception is thrown the object must be left in the no-identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.

clearIdentity

public void clearIdentity()

Put the object into the No Identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.

getIdentity

public java.lang.Object getIdentity()

Get the identity of this object.
MT - thread safe.

isDirty

public boolean isDirty()

Returns true of the object is dirty. May be called when the object is kept or unkept.
MT - thread safe

clean

public void clean(boolean forRemove)
           throws org.apache.derby.iapi.error.StandardException

Clean the object. It is up to the object to ensure synchronization of the isDirty() and clean() method calls.
If forRemove is true then the object is being removed due to an explict remove request, in this case the cache manager will have called this method regardless of the state of the isDirty()
If an exception is thrown the object must be left in the clean state.
MT - thread safe - Can be called at any time by the cache manager, it is the responsibility of the object implementing Cacheable to ensure any users of the object do not conflict with the clean call.