/*
* Licensed under the Apache License, Version 2.0 (the "License");
*
* You may not use this file except in compliance with the License.
*
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
*
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Contributions from 2013-2017 where performed either by US government
* employees, or under US Veterans Health Administration contracts.
*
* US Veterans Health Administration contributions by government employees
* are work of the U.S. Government and are not subject to copyright
* protection in the United States. Portions contributed by government
* employees are USGovWork (17USC ยง105). Not subject to copyright.
*
* Contribution by contractors to the US Veterans Health Administration
* during this period are contractually contributed under the
* Apache License, Version 2.0.
*
* See: https://www.usa.gov/government-works
*
* Contributions prior to 2013:
*
* Copyright (C) International Health Terminology Standards Development Organisation.
* Licensed under the Apache License, Version 2.0.
*
*/
package sh.isaac.api.memory;
//~--- JDK imports ------------------------------------------------------------
import java.io.BufferedOutputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.time.Duration;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.LongAdder;
//~--- non-JDK imports --------------------------------------------------------
import org.apache.mahout.math.map.HashFunctions;
import sh.isaac.api.DataSerializer;
//~--- classes ----------------------------------------------------------------
/**
* Created by kec on 4/10/15.
*
* @param <T> the generic type
*/
public class MemoryManagedReference<T extends Object>
extends SoftReference<T>
implements Comparable<MemoryManagedReference> {
/** The Constant objectIdSupplier. */
private static final AtomicInteger objectIdSupplier = new AtomicInteger();
/** The Constant referenceSequenceSupplier. */
private static final AtomicInteger referenceSequenceSupplier = new AtomicInteger(Integer.MIN_VALUE + 1);
//~--- fields --------------------------------------------------------------
/** The object id. */
private final int objectId = objectIdSupplier.getAndIncrement();
/** The last write to disk sequence. */
private int lastWriteToDiskSequence = referenceSequenceSupplier.getAndIncrement();
/** The last write to disk time. */
private long lastWriteToDiskTime = System.currentTimeMillis();
/** The last element update sequence. */
private int lastElementUpdateSequence = Integer.MIN_VALUE;
/** The last element update time. */
private long lastElementUpdateTime = System.currentTimeMillis();
/** The last element read time. */
private long lastElementReadTime = Long.MIN_VALUE;
/** The strong reference for update. */
private final AtomicReference<T> strongReferenceForUpdate = new AtomicReference<>();
/** The strong reference for cache. */
private final AtomicReference<T> strongReferenceForCache = new AtomicReference<>();
/** The hits. */
private final LongAdder hits = new LongAdder();
/** The cache count. */
private final AtomicInteger cacheCount = new AtomicInteger();
/** The disk location. */
private final File diskLocation;
/** The serializer. */
private final DataSerializer<T> serializer;
//~--- constructors --------------------------------------------------------
/**
* Instantiates a new memory managed reference.
*
* @param referent the referent
* @param diskLocation the disk location
* @param serializer the serializer
*/
public MemoryManagedReference(T referent, File diskLocation, DataSerializer<T> serializer) {
super(referent);
this.diskLocation = diskLocation;
this.serializer = serializer;
}
/**
* Instantiates a new memory managed reference.
*
* @param referent the referent
* @param q the q
* @param diskLocation the disk location
* @param serializer the serializer
*/
public MemoryManagedReference(T referent,
ReferenceQueue<? super T> q,
File diskLocation,
DataSerializer<T> serializer) {
super(referent, q);
this.diskLocation = diskLocation;
this.serializer = serializer;
}
//~--- methods -------------------------------------------------------------
/**
* Cache entry.
*/
public void cacheEntry() {
final int count = this.cacheCount.incrementAndGet();
if (count == 1) {
this.strongReferenceForCache.set(this.get());
}
}
/**
* Cache exit.
*/
public void cacheExit() {
final int count = this.cacheCount.decrementAndGet();
if (count == 0) {
this.strongReferenceForCache.set(null);
}
}
/**
* Compare to.
*
* @param o the o
* @return the int
*/
@Override
public int compareTo(MemoryManagedReference o) {
return this.objectId - o.objectId;
}
/**
* Element read.
*/
public void elementRead() {
this.hits.increment();
this.lastElementReadTime = System.currentTimeMillis();
}
/**
* Element updated.
*/
public void elementUpdated() {
this.strongReferenceForUpdate.set(this.get());
this.lastElementUpdateSequence = referenceSequenceSupplier.getAndIncrement();
this.lastElementUpdateTime = System.currentTimeMillis();
}
/**
* Equals.
*
* @param o the o
* @return true, if successful
*/
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if ((o == null) || (getClass() != o.getClass())) {
return false;
}
final MemoryManagedReference<?> that = (MemoryManagedReference<?>) o;
return this.objectId == that.objectId;
}
/**
* Hash code.
*
* @return the int
*/
@Override
public int hashCode() {
return HashFunctions.hash(this.objectId);
}
/**
* Ms since last unwritten update.
*
* @return the long
*/
public long msSinceLastUnwrittenUpdate() {
return this.lastElementUpdateTime - this.lastWriteToDiskTime;
}
/**
* Time since last read.
*
* @return the duration
*/
public Duration timeSinceLastRead() {
return Duration.ofMillis(System.currentTimeMillis() - this.lastElementReadTime);
}
/**
* Write.
*/
public void write() {
final T objectToWrite = this.strongReferenceForUpdate.get();
if (objectToWrite != null) {
this.strongReferenceForUpdate.set(null);
DiskSemaphore.acquire();
this.lastWriteToDiskSequence = referenceSequenceSupplier.getAndIncrement();
this.lastWriteToDiskTime = System.currentTimeMillis();
this.diskLocation.getParentFile()
.mkdirs();
try (DataOutputStream out =
new DataOutputStream(new BufferedOutputStream(new FileOutputStream(this.diskLocation)))) {
this.serializer.serialize(out, objectToWrite);
} catch (final FileNotFoundException e) {
throw new RuntimeException(e);
} catch (final IOException e) {
throw new RuntimeException(e);
} finally {
DiskSemaphore.release();
}
}
}
//~--- get methods ---------------------------------------------------------
/**
* Gets the last write to disk time.
*
* @return the last write to disk time
*/
public long getLastWriteToDiskTime() {
return this.lastWriteToDiskTime;
}
/**
* Checks for unwritten update.
*
* @return true, if successful
*/
public boolean hasUnwrittenUpdate() {
return this.lastWriteToDiskSequence < this.lastElementUpdateSequence;
}
}