java.lang.Object
java.util.AbstractMap
org.vrspace.neurogrid.SoftCache
- All Implemented Interfaces:
- java.util.Map
- public class SoftCache
- extends java.util.AbstractMap
MRU Memory-Sensitive SoftCache
This SoftCache implements storage in an MRU fashion. Every time an object is retrieved
with get 55 , that object is put at the head of the MRU list.
In the constructor, SoftCache 55 , the maximum size of the MRU list can
be specified. Any item that has been #put{Object,Object put} which is not
on the MRU list is susceptible to being garbage collected. All values in this Map
are stored via SoftReferences. Objects that
are only softly reachable are eligible for reclamation by the garbage collector when
there are only soft references to them. In this context, this would mean there is
no thread which could follow a chain of references to get to the object - the only
reference to the object is within this map. The garbage collector is required to
clear all soft references before throwing an OutOfMemoryError.
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Nested Class Summary |
class |
SoftCache.MRUMap
|
protected class |
SoftCache.SoftValue
Internal class to allow for easy removal of key-value pair
when value has been reclaimed from SoftReference |
| Nested classes inherited from class java.util.AbstractMap |
|
| Nested classes inherited from class java.util.Map |
java.util.Map.Entry |
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Constructor Summary |
SoftCache()
Default constructor instantiates SoftCache with a default size of 100 items |
SoftCache(int mruSize)
Constructor allowing for parameterization of mru size. |
SoftCache
java.util.Map SoftCache
mruSize
int mruSize
SoftCacheQueue
java.lang.ref.ReferenceQueue SoftCacheQueue
mruMap
java.util.LinkedHashMap mruMap
keysRemoved
int keysRemoved
SoftCache
public SoftCache()
- Default constructor instantiates SoftCache with a default size of 100 items
SoftCache
public SoftCache(int mruSize)
- Constructor allowing for parameterization of mru size.
get
public java.lang.Object get(java.lang.Object key)
- Retreives an object from the SoftCache. If there is a value that
corresponds to the key it is returned and that key is placed
at the head of the MRU list. If the key points to a value
that has been reclaimed by the garbage collector, that key is
removed from the backing Map.
processQueue
protected void processQueue()
- Removes keys for SoftReferences that have been enqueued.
Altered from DevX version for clarity
put
public java.lang.Object put(java.lang.Object key,
java.lang.Object value)
- Stores an object to the SoftCache. Before storing the value, the
SoftCache takes the opportunity to clear any SoftReferences that
have been enqueued.
memorySensitiveCallback
public boolean memorySensitiveCallback(java.lang.reflect.Method callback,
java.lang.Object target,
java.lang.Object[] args)
- Executes method callback on Object
target with arguments args. If that method throws an
OutOfMemoryError,
the oldest half of the MRU SoftCache is dumped - allowing for these
entries to be garbage collected. The method is then invoked again,
and this proceeds in a recursive fashion - for example if the method
throws an OutOfMemoryError after half of the MRU SoftCache has been dropped,
half of the remaining MRU SoftCache is dropped. When the MRU SoftCache is
emptied, the OutOfMemoryError is thrown back up the call stack to the
original caller of this method. What is being considered is to make
this a static method that operates on all of the instances of SoftCache
at the same time.
remove
public java.lang.Object remove(java.lang.Object key)
- Removes an object from the SoftCache. If the object exists in the SoftCache,
its SoftReference is checked to see if the value has been reclaimed.
If it has not been reclaimed, the value is returned - otherwise, null
is returned. It is not a problem if this value is in the MRU list,
since this value will eventually drop off the list.
size
public int size()
- Returns size of SoftCache. The SoftCache takes this opportunity to release
any enqueued SoftReferences.
clear
public void clear()
- Clears SoftCache, MRU list. The SoftCache takes this opportunity to release
any enqueued SoftReferences.
entrySet
public java.util.Set entrySet()
- Throws an UnsupportedOperationException
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