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package com.techempower.cache;
import gnu.trove.map.*;
import gnu.trove.map.hash.*;
import java.lang.reflect.*;
import java.util.*;
import java.util.concurrent.*;
import com.techempower.data.*;
import com.techempower.helper.*;
import com.techempower.util.*;
/**
* This class is a simple data structure that holds objects of a particular
* unspecified type, keyed by an long identifier. It can be limited to a
* particular size, and will trim itself if it exceeds that size.
*
* This is a default implementation of a CacheGroup that can be extended by
* applications to have custom behaviors. For example, the trim methods may be
* extended to use a LRU (Least-Recently Used) replacement algorithm.
*
* We avoid thread synchronization on read operations (getting objects). Write
* operations (adding, removing objects for example) are synchronized.
*
* Read operations are made threadsafe without synchronization through the use
* of CopyOnWriteArrayList (from the Java concurrency package) and
* ConcurrentLongMap, which is a simple re-working of ConcurrentHashMap also
* from the Java concurrency package.
*
* Testing so far indicates read performance that is greatly improved over
* previous versions that used synchronization for both reads and writes.
*/
public class CacheGroup
extends EntityGroup
implements Initializable
{
//
// Member variables.
//
private ConcurrentMap objects = new ConcurrentHashMap<>();
private List objectsInOrder = new CopyOnWriteArrayList<>();
private volatile boolean initialized = false;
private boolean errorOnInitialize = false;
private long lowestIdentity = Long.MAX_VALUE;
private long highestIdentity = 0;
//
// Member methods.
//
/**
* Constructor.
*/
protected CacheGroup(EntityStore controller,
Class type,
String table,
String id,
EntityMaker maker,
Comparator comparator,
String where,
String[] whereArguments,
boolean readOnly)
{
super(controller, type, table, id, maker, comparator,
where, whereArguments, readOnly);
}
/**
* Creates a new {@link Builder}, which is used to construct an
* {@link CacheGroup}. Example usage:
*
*
* CacheGroup<Foo> = CacheGroup.of(Foo.class) // new Builder
* .table("foos") // modified Builder
* .id("fooID") // modified Builder
* .build(controller); // new CacheGroup
*
*
* Note that a {@link EntityStore#register(EntityGroup.Builder)} method
* exists, so in the common case where you only want to register the group and
* don't care to retain your own reference to it, calling
* {@code .build(controller)} is unnecessary. For example:
*
*
* register(CacheGroup.of(Foo.class) // new Builder
* .table("foos") // modified Builder
* .id("fooID") // modified Builder
* ); // the register method calls .build(controller) for us
*
*
* @param type The type of the entities.
* @return A new {@link Builder}.
*/
public static Builder of(Class type)
{
return new Builder<>(type);
}
/**
* Sets the objects list to the contents of the provided Collection.
*/
public void setObjects(Collection objects)
{
if (readOnly())
{
throw new EntityException("EntityGroup for " + name()
+ " is read-only. The \"setObjects\" method is not permitted.");
}
synchronized (this)
{
if (objects == null)
{
this.objects = new ConcurrentHashMap<>();
this.objectsInOrder = new CopyOnWriteArrayList<>();
}
else
{
final ConcurrentMap workMap = new ConcurrentHashMap<>(
objects.size());
final List workList = new ArrayList<>(objects.size());
for (T object : objects)
{
workMap.put(object.getId(), object);
workList.add(object);
}
// Replace the member variables.
this.objects = workMap;
this.objectsInOrder = new CopyOnWriteArrayList<>(workList);
// If we're setting objects from somewhere else, we should assume
// that this is initializing the cache group.
setInitialized(true);
}
// Recalculate high and low identities if these high/low values have
// been used in the past.
calculateHighLowIdentitiesRecalc();
}
}
/**
* Resets this group, removing all the objects, and setting the initialized
* flag to false. The group will be rebuilt from the database on next use.
*/
@Override
public void reset()
{
synchronized (this)
{
setInitialized(false);
// Instantiate a new object so that any threads currently working with
// an old reference outside of a synchronized block will not be
// affected.
this.objects = new ConcurrentHashMap<>();
this.objectsInOrder = new CopyOnWriteArrayList<>();
setErrorOnInitialize(false);
resetHighLowIdentities();
}
}
@Override
public T get(long id)
{
initializeIfNecessary();
return this.objects.get(id);
}
/**
* Gets an object from the objects map in a raw manner--that is, calling
* the map's get method directly without any pre-initialization.
*/
protected T getRaw(long id)
{
return this.objects.get(id);
}
/**
* Returns an array of objects specified by the identities provided in
* an long array parameter. This formerly provided a performance advantage
* over multiple calls to getObject, but that is no longer the case. It
* remains as a convenience method.
*
* The array will contain null in any indexes for which an object was not
* found for the associated identity.
*
* @param identities an long[] of object identities
*/
public Identifiable[] select(long[] identities)
{
final Identifiable[] toReturn = new Identifiable[identities.length];
initializeIfNecessary();
for (int i = 0; i < identities.length; i++)
{
toReturn[i] = this.objects.get(identities[i]);
}
return toReturn;
}
@Override
public List list()
{
initializeIfNecessary();
return new ArrayList<>(this.objectsInOrder);
}
@Override
public TLongObjectMap map()
{
initializeIfNecessary();
// Grab a reference.
final ConcurrentMap map = this.objects;
final TLongObjectMap toReturn = new TLongObjectHashMap<>(map.size());
final Iterator values = map.values().iterator();
T object;
while (values.hasNext())
{
object = values.next();
toReturn.put(object.getId(), object);
}
return toReturn;
}
/**
* Add an object to the cache and the data store.
*/
@Override
public void put(T object)
{
if (readOnly())
{
throw new EntityException("EntityGroup for " + name()
+ " is read-only. The \"put\" method is not permitted.");
}
initializeIfNecessary();
// Get a snapshot of the current persistence state.
final boolean persisted = isPersisted(object);
// Persist the object.
putPersistent(object);
if (persisted)
{
// Object was already persisted, so let's reorder in case the field
// we are ordered by was changed.
reorder(object.getId());
}
else
{
// Object was not persisted, so let's add it to the cache.
addToCache(object);
}
}
/**
* Called by CacheGroup.put to persist an entity to the database via a
* call to the method of the same name provided by the superclass:
* EntityGroup.put.
*
* This method is exposed as a protected class to allow subclasses to
* specialize the persistence behavior.
*/
protected void putPersistent(T object)
{
// Ask the EntityGroup parent to persist the changes.
super.put(object);
}
/**
* Add objects to the cache and the data store.
*/
@SuppressWarnings("unchecked")
@Override
public void putAll(Collection objectsToPut)
{
if (readOnly())
{
throw new EntityException("EntityGroup for " + name()
+ " is read-only. The \"putAll\" method is not permitted.");
}
initializeIfNecessary();
// Get a snapshot of the current persistence state.
final List persisted = new ArrayList<>(objectsToPut.size());
final List nonPersisted = new ArrayList<>(objectsToPut.size());
for (T object : objectsToPut)
{
if (isPersisted(object))
{
persisted.add(object.getId());
}
else
{
nonPersisted.add(object);
}
}
// Persist the changes.
putAllPersistent(objectsToPut);
// Reorder any previously-persisted objects in case the field we are
// ordered by was changed.
reorder(CollectionHelper.toLongArray(persisted));
// Add any objects we did not previously know about.
addToCache(nonPersisted.toArray((T[])Array.newInstance(type(), nonPersisted.size())));
}
/**
* Called by CacheGroup.putAll to persist a list of entities to the
* database via a call to the method of the same name provided by the
* superclass: EntityGroup.putAll.
*
* This method is exposed as a protected class to allow subclasses to
* specialize the persistence behavior.
*/
protected void putAllPersistent(Collection objectsToPut)
{
// Ask the EntityGroup parent to persist the objects.
super.putAll(objectsToPut);
}
/**
* Remove an object from the cache and the data store.
*/
@Override
public void remove(long id)
{
if (readOnly())
{
throw new EntityException("EntityGroup for " + name()
+ " is read-only. The \"remove\" method is not permitted.");
}
initializeIfNecessary();
// Remove the persistent instance of the object.
removePersistent(id);
// Remove it from the cache.
removeFromCache(id);
}
/**
* Called by CacheGroup.remove to remove an object from the persistent
* store (database).
*
* This method is exposed as a protected class to allow subclasses to
* specialize the persistence behavior.
*/
protected void removePersistent(long id)
{
// Ask the EntityGroup parent to remove the persisted object.
super.remove(id);
}
/**
* Add objects to the cache only, not affecting the data store.
*/
@SafeVarargs
public final void addToCache(T... objectsToAdd)
{
// Grab references.
final ConcurrentMap map = this.objects;
final List orderedList = this.objectsInOrder;
synchronized (this)
{
for (T object : objectsToAdd)
{
// Only proceed if we don't already have this reference in the cache.
if (!map.containsValue(object))
{
// If we already have a reference with the same ID, let's remove it.
if (map.containsKey(object.getId()))
{
// Remove the existing reference from the ordered list.
orderedList.remove(map.get(object.getId()));
}
map.put(object.getId(), object);
int search = Collections.binarySearch(orderedList, object, comparator());
if (search < 0)
{
orderedList.add(-search - 1, object);
}
else
{
orderedList.add(object);
}
if (areHighLowIdentitiesInitialized())
{
if (object.getId() < this.lowestIdentity)
{
this.lowestIdentity = object.getId();
}
if (object.getId() > this.highestIdentity)
{
this.highestIdentity = object.getId();
}
}
}
}
}
}
/**
* Removes an object from the cache only, not affecting the data store.
*/
public boolean removeFromCache(T object)
{
return removeFromCache(object.getId());
}
/**
* Removes objects from the cache only, not affecting the data store.
*/
public boolean removeFromCache(long... ids)
{
// Grab references.
final ConcurrentMap map = this.objects;
final List orderedList = this.objectsInOrder;
synchronized (this)
{
for (long id : ids)
{
orderedList.remove(map.remove(id));
}
// Recalculate high/low identities if needed.
calculateHighLowIdentitiesRecalc();
return true;
}
}
/**
* Does the cacheGroup contain this particular object?
*
* @param object The object to search for.
*/
public boolean contains(T object)
{
initializeIfNecessary();
return this.objects.containsValue(object);
}
/**
* Does the cacheGroup contain this particular object as specified
* by the identifier?
*
* @param id The ID (identifier) to search for.
*/
public boolean contains(long id)
{
initializeIfNecessary();
return this.objects.containsKey(id);
}
/**
* Returns the result of calling the objects map's contains method without
* any pre-initialization.
*/
protected boolean containsRaw(long id)
{
return this.objects.containsKey(id);
}
/**
* Returns the result of calling the objects map's contains method without
* any pre-initialization.
*/
protected boolean containsRaw(Identifiable object)
{
return this.objects.containsValue(object);
}
/**
* If true, this indicates that a database failure caused initialization
* to fail.
*/
public boolean isErrorOnInitialize()
{
return this.errorOnInitialize;
}
/**
* When fetching a cache group's contents from the database, the cache
* controller may set this flag to true to indicate that an error was
* encountered during initialization.
*/
public void setErrorOnInitialize(boolean errorOnInitialize)
{
this.errorOnInitialize = errorOnInitialize;
}
/**
* Calls initialize() if the Cache Group has not already been initialized.
* That is, if the initialized flag is false.
*/
public void initializeIfNecessary()
{
if (!this.initialized)
{
synchronized (this)
{
if (!this.initialized)
{
initialize();
}
}
}
}
/**
* Initializes this CacheGroup.
*/
@Override
public void initialize()
{
synchronized (this)
{
this.objectsInOrder = new CopyOnWriteArrayList<>(fetchAllPersistedObjects());
copyOrderedObjectsToMap();
// Reset the high and low identities.
resetHighLowIdentities();
setInitialized(true);
// Execute custom post-initialization processing.
customPostInitialization();
}
}
/**
* Called by initialize to fetch a list of persistent entities using the
* EntityGroup.list method.
*/
protected List fetchAllPersistedObjects()
{
return super.list();
}
/**
* Executes custom post-initialization processing for the group. Note that
* the group will remain blocked (within the initialization "synchronized"
* block) until this method returns. Post-initialization processing should
* therefore be as quick as possible.
*/
protected void customPostInitialization()
{
// Does nothing in this base class.
}
/**
* Copies ordered objects to the LongMap.
*/
protected void copyOrderedObjectsToMap()
{
final Iterator iter = this.objectsInOrder.iterator();
// Create a new map, work, to populate.
final ConcurrentMap work = new ConcurrentHashMap<>(
this.objectsInOrder.size());
T co;
while (iter.hasNext())
{
co = iter.next();
work.put(co.getId(), co);
}
// Replace the member variable.
this.objects = work;
}
/**
* Sets the initialized flag.
*
* Calls to initialize should set the initialized flag to true.
*
* Calls to reset will set the initialized flag to false.
*/
protected void setInitialized(boolean initialized)
{
this.initialized = initialized;
}
/**
* Gets the initialized variable. See setInitialized.
*/
@Override
public boolean isInitialized()
{
return this.initialized;
}
@Override
public long lowest()
{
calculateHighLowIdentitiesInitial();
return this.lowestIdentity;
}
@Override
public long highest()
{
calculateHighLowIdentitiesInitial();
return this.highestIdentity;
}
/**
* Resets the highest and lowest identity member variables.
*/
protected void resetHighLowIdentities()
{
this.lowestIdentity = Long.MAX_VALUE;
this.highestIdentity = 0;
}
/**
* Determines if the highest and lowest identity member variables have
* been initialized (whether they have been used).
*/
protected boolean areHighLowIdentitiesInitialized()
{
return ( (this.lowestIdentity < Long.MAX_VALUE)
|| (this.highestIdentity > 0)
);
}
/**
* Determines the highest and lowest identity of objects in the group
* and store these values in the member variables.
*/
protected void calculateHighLowIdentities()
{
final Iterator iter = this.objectsInOrder.iterator();
Identifiable co;
long id;
while (iter.hasNext())
{
co = (Identifiable)iter.next();
id = co.getId();
if (id < this.lowestIdentity)
{
this.lowestIdentity = id;
}
if (id > this.highestIdentity)
{
this.highestIdentity = id;
}
}
}
/**
* Calculates the high and low identities if they have not yet been
* calculated. This is called by getLowestIdentity and getHighestIdentity
* to allow for lazy-initialization of these member variables.
*/
protected void calculateHighLowIdentitiesInitial()
{
if (!areHighLowIdentitiesInitialized())
{
calculateHighLowIdentities();
}
}
/**
* Recalculates high and low identities only if they have been initialized.
* This is used when objects are added to the collection but only when
* the high/low values have been used in the past. This avoids the
* computation expense if the application never uses these methods.
*/
protected void calculateHighLowIdentitiesRecalc()
{
if (areHighLowIdentitiesInitialized())
{
calculateHighLowIdentities();
}
}
/**
* Returns the current size of the cacheGroup.
*/
@Override
public int size()
{
initializeIfNecessary();
return this.objects.size();
}
/**
* This method ensures that the next time the specified objects are
* fetched, they will be at least as current as the time of this method
* call.
*
* @param ids the ids of the objects
*/
@Override
public void refresh(long... ids)
{
// Grab references.
final ConcurrentMap map = this.objects;
final List orderedList = this.objectsInOrder;
synchronized (this)
{
// If the group is not initialized, we're done.
if (!this.initialized)
{
return;
}
// Fetch the new objects.
final TLongObjectMap objectsMap = super.map(CollectionHelper.toList(ids));
for (long id : ids)
{
// Remove the object with this id from the cache, if it's there.
orderedList.remove(map.remove(id));
final T object = objectsMap.get(id);
// Put the newly loaded object into the cache.
if (object != null)
{
map.put(id, object);
// Use the comparator to insert it at the appropriate position.
int search = Collections.binarySearch(orderedList, object, comparator());
if (search < 0)
{
orderedList.add(-search - 1, object);
}
else
{
orderedList.add(object);
}
}
}
}
}
/**
* This method ensures that the next time the ordered objects are fetched,
* the specified objects will be in the correct positions.
*
* @param ids the ids of the objects
*/
@Override
public void reorder(long... ids)
{
// Grab references.
final ConcurrentMap map = this.objects;
final List orderedList = this.objectsInOrder;
synchronized (this)
{
// If the group is not initialized, we're done.
if (!this.initialized)
{
return;
}
for (long id : ids)
{
final T object = map.get(id);
if (object != null)
{
// Since writes to the list are expensive, let's see if it's already
// in the correct order before modifying anything.
final int index = orderedList.indexOf(object);
final T previous = (index == 0)
? null
: orderedList.get(index - 1);
final T next = (index == this.objectsInOrder.size() - 1)
? null
: orderedList.get(index + 1);
if ((previous == null || comparator().compare(object, previous) >= 0)
&& (next == null || comparator().compare(object, next) <= 0))
{
return;
}
// Boo, it's out of order. We need to do two write operations now,
// which causes the list to copy itself twice.
orderedList.remove(object);
final int search = Collections.binarySearch(orderedList, object,
comparator());
if (search < 0)
{
orderedList.add(-search - 1, object);
}
else
{
orderedList.add(object);
}
}
}
}
}
@Override
public String toString()
{
return "CacheGroup [" + name() + "]";
}
@Override
public void removeAll(Collection ids)
{
if (readOnly())
{
throw new EntityException("EntityGroup for " + name()
+ " is read-only. The \"removeAll\" method is not permitted.");
}
initializeIfNecessary();
// Ask the EntityGroup parent to persist the changes.
removeAllPersistent(ids);
// Remove it from the cache.
this.removeFromCache(CollectionHelper.toLongArray(ids));
}
/**
* Called by CacheGroup.removeAll to remove a collection of objects from the
* persistent store (database).
*
* This method is exposed as a protected class to allow subclasses to
* specialize the persistence behavior.
*/
protected void removeAllPersistent(Collection ids)
{
// Ask the EntityGroup parent to persist the changes.
super.removeAll(ids);
}
@Override
public List list(Collection ids)
{
initializeIfNecessary();
final List theObjects = new ArrayList<>(ids.size());
for (long id : ids)
{
final T object = this.objects.get(id);
if (object != null)
{
theObjects.add(object);
}
}
return theObjects;
}
@Override
public TLongObjectMap map(Collection ids)
{
initializeIfNecessary();
final TLongObjectMap theObjects = new TLongObjectHashMap<>(ids.size());
for (long id : ids)
{
final T object = this.objects.get(id);
if (object != null)
{
theObjects.put(id, object);
}
}
return theObjects;
}
//
// Inner classes.
//
/**
* Creates new instances of {@code CacheGroup}.
*/
public static class Builder
extends EntityGroup.Builder
{
protected Builder(Class type)
{
super(type);
}
@Override
public CacheGroup build(EntityStore controller)
{
if (controller == null)
{
throw new NullPointerException();
}
return new CacheGroup<>(
controller,
this.type,
this.table,
this.id,
this.maker,
this.comparator,
this.where,
this.whereArguments,
this.readOnly);
}
@Override
public Builder table(String tableName)
{
super.table(tableName);
return this;
}
@Override
public Builder id(String idFieldName)
{
super.id(idFieldName);
return this;
}
@Override
public Builder readOnly()
{
super.readOnly();
return this;
}
@Override
public Builder maker(EntityMaker entityMaker)
{
super.maker(entityMaker);
return this;
}
@Override
public Builder comparator(Comparator entityComparator)
{
super.comparator(entityComparator);
return this;
}
@Override
public Builder comparator(String methodName)
{
super.comparator(methodName);
return this;
}
@Override
public Builder where(String whereClause, String... arguments)
{
super.where(whereClause, arguments);
return this;
}
@Override
public Builder constructorArgs(Object... arguments)
{
super.constructorArgs(arguments);
return this;
}
} // End Builder.
} // End CacheGroup.