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/*
* Copyright 2014 Ben Manes. All Rights Reserved.
*
* 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.
*/
package com.github.benmanes.caffeine.cache;
import static com.github.benmanes.caffeine.cache.Async.ASYNC_EXPIRY;
import static com.github.benmanes.caffeine.cache.Caffeine.ceilingPowerOfTwo;
import static com.github.benmanes.caffeine.cache.Caffeine.requireArgument;
import static com.github.benmanes.caffeine.cache.Caffeine.requireState;
import static com.github.benmanes.caffeine.cache.LocalLoadingCache.newBulkMappingFunction;
import static com.github.benmanes.caffeine.cache.LocalLoadingCache.newMappingFunction;
import static com.github.benmanes.caffeine.cache.Node.PROBATION;
import static com.github.benmanes.caffeine.cache.Node.PROTECTED;
import static com.github.benmanes.caffeine.cache.Node.WINDOW;
import static java.util.Objects.requireNonNull;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Optional;
import java.util.OptionalInt;
import java.util.OptionalLong;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
import com.github.benmanes.caffeine.cache.Async.AsyncExpiry;
import com.github.benmanes.caffeine.cache.LinkedDeque.PeekingIterator;
import com.github.benmanes.caffeine.cache.References.InternalReference;
import com.github.benmanes.caffeine.cache.stats.StatsCounter;
import com.google.errorprone.annotations.concurrent.GuardedBy;
/**
* An in-memory cache implementation that supports full concurrency of retrievals, a high expected
* concurrency for updates, and multiple ways to bound the cache.
*
* This class is abstract and code generated subclasses provide the complete implementation for a
* particular configuration. This is to ensure that only the fields and execution paths necessary
* for a given configuration are used.
*
* @author [email protected] (Ben Manes)
* @param the type of keys maintained by this cache
* @param the type of mapped values
*/
@SuppressWarnings("deprecation")
abstract class BoundedLocalCache extends BLCHeader.DrainStatusRef
implements LocalCache {
/*
* This class performs a best-effort bounding of a ConcurrentHashMap using a page-replacement
* algorithm to determine which entries to evict when the capacity is exceeded.
*
* Concurrency:
* ------------
* The page replacement algorithms are kept eventually consistent with the map. An update to the
* map and recording of reads may not be immediately reflected on the policy's data structures.
* These structures are guarded by a lock and operations are applied in batches to avoid lock
* contention. The penalty of applying the batches is spread across threads so that the amortized
* cost is slightly higher than performing just the ConcurrentHashMap operation [1].
*
* A memento of the reads and writes that were performed on the map are recorded in buffers. These
* buffers are drained at the first opportunity after a write or when a read buffer is full. The
* reads are offered to a buffer that will reject additions if contended on or if it is full. Due
* to the concurrent nature of the read and write operations a strict policy ordering is not
* possible, but may be observably strict when single threaded. The buffers are drained
* asynchronously to minimize the request latency and uses a state machine to determine when to
* schedule this work on an executor.
*
* Due to a lack of a strict ordering guarantee, a task can be executed out-of-order, such as a
* removal followed by its addition. The state of the entry is encoded using the key field to
* avoid additional memory. An entry is "alive" if it is in both the hash table and the page
* replacement policy. It is "retired" if it is not in the hash table and is pending removal from
* the page replacement policy. Finally an entry transitions to the "dead" state when it is not in
* the hash table nor the page replacement policy. Both the retired and dead states are
* represented by a sentinel key that should not be used for map operations.
*
* Eviction:
* ---------
* Maximum size is implemented using the Window TinyLfu policy [2] due to its high hit rate, O(1)
* time complexity, and small footprint. A new entry starts in the admission window and remains
* there as long as it has high temporal locality (recency). Eventually an entry will slip from
* the window into the main space. If the main space is already full, then a historic frequency
* filter determines whether to evict the newly admitted entry or the victim entry chosen by the
* eviction policy. This process ensures that the entries in the window were very recently used
* and entries in the main space are accessed very frequently and are moderately recent. The
* windowing allows the policy to have a high hit rate when entries exhibit bursty access pattern
* while the filter ensures that popular items are retained. The admission window uses LRU and
* the main space uses Segmented LRU.
*
* The optimal size of the window vs main spaces is workload dependent [3]. A large admission
* window is favored by recency-biased workloads while a small one favors frequency-biased
* workloads. When the window is too small then recent arrivals are prematurely evicted, but when
* too large then they pollute the cache and force the eviction of more popular entries. The
* configuration is dynamically determined using hill climbing to walk the hit rate curve. This is
* done by sampling the hit rate and adjusting the window size in the direction that is improving
* (making positive or negative steps). At each interval the step size is decreased until the
* climber converges at the optimal setting. The process is restarted when the hit rate changes
* over a threshold, indicating that the workload altered and a new setting may be required.
*
* The historic usage is retained in a compact popularity sketch, which uses hashing to
* probabilistically estimate an item's frequency. This exposes a flaw where an adversary could
* use hash flooding [4] to artificially raise the frequency of the main space's victim and cause
* all candidates to be rejected. In the worst case, by exploiting hash collisions an attacker
* could cause the cache to never hit and hold only worthless items, resulting in a
* denial-of-service attack against the underlying resource. This is protected against by
* introducing jitter so that candidates which are at least moderately popular have a small,
* random chance of being admitted. This causes the victim to be evicted, but in a way that
* marginally impacts the hit rate.
*
* Expiration:
* -----------
* Expiration is implemented in O(1) time complexity. The time-to-idle policy uses an access-order
* queue, the time-to-live policy uses a write-order queue, and variable expiration uses a
* hierarchical timer wheel [5]. The queuing policies allow for peeking at the oldest entry to
* see if it has expired and, if it has not, then the younger entries must not have too. If a
* maximum size is set then expiration will share the queues so that the per-entry footprint is
* minimized. The timer wheel based policy uses hashing and cascading in a manner that amortizes
* the penalty of sorting to achieve a similar algorithmic cost.
*
* The expiration updates are applied in a best effort fashion. The reordering of variable or
* access-order expiration may be discarded by the read buffer if full or contended on. Similarly
* the reordering of write expiration may be ignored for an entry if the last update was within a
* short time window in order to avoid overwhelming the write buffer.
*
* [1] BP-Wrapper: A Framework Making Any Replacement Algorithms (Almost) Lock Contention Free
* http://web.cse.ohio-state.edu/hpcs/WWW/HTML/publications/papers/TR-09-1.pdf
* [2] TinyLFU: A Highly Efficient Cache Admission Policy
* https://dl.acm.org/citation.cfm?id=3149371
* [3] Adaptive Software Cache Management
* https://dl.acm.org/citation.cfm?id=3274816
* [4] Denial of Service via Algorithmic Complexity Attack
* https://www.usenix.org/legacy/events/sec03/tech/full_papers/crosby/crosby.pdf
* [5] Hashed and Hierarchical Timing Wheels
* http://www.cs.columbia.edu/~nahum/w6998/papers/ton97-timing-wheels.pdf
*/
static final Logger logger = Logger.getLogger(BoundedLocalCache.class.getName());
/** The number of CPUs */
static final int NCPU = Runtime.getRuntime().availableProcessors();
/** The initial capacity of the write buffer. */
static final int WRITE_BUFFER_MIN = 4;
/** The maximum capacity of the write buffer. */
static final int WRITE_BUFFER_MAX = 128 * ceilingPowerOfTwo(NCPU);
/** The number of attempts to insert into the write buffer before yielding. */
static final int WRITE_BUFFER_RETRIES = 100;
/** The maximum weighted capacity of the map. */
static final long MAXIMUM_CAPACITY = Long.MAX_VALUE - Integer.MAX_VALUE;
/** The initial percent of the maximum weighted capacity dedicated to the main space. */
static final double PERCENT_MAIN = 0.99d;
/** The percent of the maximum weighted capacity dedicated to the main's protected space. */
static final double PERCENT_MAIN_PROTECTED = 0.80d;
/** The difference in hit rates that restarts the climber. */
static final double HILL_CLIMBER_RESTART_THRESHOLD = 0.05d;
/** The percent of the total size to adapt the window by. */
static final double HILL_CLIMBER_STEP_PERCENT = 0.0625d;
/** The rate to decrease the step size to adapt by. */
static final double HILL_CLIMBER_STEP_DECAY_RATE = 0.98d;
/** The maximum number of entries that can be transfered between queues. */
static final int QUEUE_TRANSFER_THRESHOLD = 1_000;
/** The maximum time window between entry updates before the expiration must be reordered. */
static final long EXPIRE_WRITE_TOLERANCE = TimeUnit.SECONDS.toNanos(1);
/** The maximum duration before an entry expires. */
static final long MAXIMUM_EXPIRY = (Long.MAX_VALUE >> 1); // 150 years
final MpscGrowableArrayQueue writeBuffer;
final ConcurrentHashMap> data;
@Nullable final CacheLoader cacheLoader;
final PerformCleanupTask drainBuffersTask;
final Consumer> accessPolicy;
final Buffer> readBuffer;
final NodeFactory nodeFactory;
final ReentrantLock evictionLock;
final CacheWriter writer;
final Weigher weigher;
final Executor executor;
final boolean isAsync;
// The collection views
@Nullable transient Set keySet;
@Nullable transient Collection values;
@Nullable transient Set> entrySet;
/** Creates an instance based on the builder's configuration. */
protected BoundedLocalCache(Caffeine builder,
@Nullable CacheLoader cacheLoader, boolean isAsync) {
this.isAsync = isAsync;
this.cacheLoader = cacheLoader;
executor = builder.getExecutor();
evictionLock = new ReentrantLock();
weigher = builder.getWeigher(isAsync);
writer = builder.getCacheWriter(isAsync);
drainBuffersTask = new PerformCleanupTask(this);
nodeFactory = NodeFactory.newFactory(builder, isAsync);
data = new ConcurrentHashMap<>(builder.getInitialCapacity());
readBuffer = evicts() || collectKeys() || collectValues() || expiresAfterAccess()
? new BoundedBuffer<>()
: Buffer.disabled();
accessPolicy = (evicts() || expiresAfterAccess()) ? this::onAccess : e -> {};
writeBuffer = new MpscGrowableArrayQueue<>(WRITE_BUFFER_MIN, WRITE_BUFFER_MAX);
if (evicts()) {
setMaximumSize(builder.getMaximum());
}
}
/* --------------- Shared --------------- */
/** Returns if the node's value is currently being computed, asynchronously. */
final boolean isComputingAsync(Node node) {
return isAsync && !Async.isReady((CompletableFuture) node.getValue());
}
@GuardedBy("evictionLock")
protected AccessOrderDeque> accessOrderWindowDeque() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected AccessOrderDeque> accessOrderProbationDeque() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected AccessOrderDeque> accessOrderProtectedDeque() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected WriteOrderDeque> writeOrderDeque() {
throw new UnsupportedOperationException();
}
@Override
public final Executor executor() {
return executor;
}
/** Returns whether this cache notifies a writer when an entry is modified. */
protected boolean hasWriter() {
return (writer != CacheWriter.disabledWriter());
}
/* --------------- Stats Support --------------- */
@Override
public boolean isRecordingStats() {
return false;
}
@Override
public StatsCounter statsCounter() {
return StatsCounter.disabledStatsCounter();
}
@Override
public Ticker statsTicker() {
return Ticker.disabledTicker();
}
/* --------------- Removal Listener Support --------------- */
@Override
@SuppressWarnings("NullAway")
public RemovalListener removalListener() {
return null;
}
@Override
public boolean hasRemovalListener() {
return false;
}
@Override
public void notifyRemoval(@Nullable K key, @Nullable V value, RemovalCause cause) {
requireState(hasRemovalListener(), "Notification should be guarded with a check");
Runnable task = () -> {
try {
removalListener().onRemoval(key, value, cause);
} catch (Throwable t) {
logger.log(Level.WARNING, "Exception thrown by removal listener", t);
}
};
try {
executor.execute(task);
} catch (Throwable t) {
logger.log(Level.SEVERE, "Exception thrown when submitting removal listener", t);
task.run();
}
}
/* --------------- Reference Support --------------- */
/** Returns if the keys are weak reference garbage collected. */
protected boolean collectKeys() {
return false;
}
/** Returns if the values are weak or soft reference garbage collected. */
protected boolean collectValues() {
return false;
}
@SuppressWarnings("NullAway")
protected ReferenceQueue keyReferenceQueue() {
return null;
}
@SuppressWarnings("NullAway")
protected ReferenceQueue valueReferenceQueue() {
return null;
}
/* --------------- Expiration Support --------------- */
/** Returns the {@link Pacer} used to schedule the maintenance task. */
protected @Nullable Pacer pacer() {
return null;
}
/** Returns if the cache expires entries after a variable time threshold. */
protected boolean expiresVariable() {
return false;
}
/** Returns if the cache expires entries after an access time threshold. */
protected boolean expiresAfterAccess() {
return false;
}
/** Returns how long after the last access to an entry the map will retain that entry. */
protected long expiresAfterAccessNanos() {
throw new UnsupportedOperationException();
}
protected void setExpiresAfterAccessNanos(long expireAfterAccessNanos) {
throw new UnsupportedOperationException();
}
/** Returns if the cache expires entries after an write time threshold. */
protected boolean expiresAfterWrite() {
return false;
}
/** Returns how long after the last write to an entry the map will retain that entry. */
protected long expiresAfterWriteNanos() {
throw new UnsupportedOperationException();
}
protected void setExpiresAfterWriteNanos(long expireAfterWriteNanos) {
throw new UnsupportedOperationException();
}
/** Returns if the cache refreshes entries after an write time threshold. */
protected boolean refreshAfterWrite() {
return false;
}
/** Returns how long after the last write an entry becomes a candidate for refresh. */
protected long refreshAfterWriteNanos() {
throw new UnsupportedOperationException();
}
protected void setRefreshAfterWriteNanos(long refreshAfterWriteNanos) {
throw new UnsupportedOperationException();
}
@Override
public boolean hasWriteTime() {
return expiresAfterWrite() || refreshAfterWrite();
}
@SuppressWarnings("NullAway")
protected Expiry expiry() {
return null;
}
@Override
public Ticker expirationTicker() {
return Ticker.disabledTicker();
}
protected TimerWheel timerWheel() {
throw new UnsupportedOperationException();
}
/* --------------- Eviction Support --------------- */
/** Returns if the cache evicts entries due to a maximum size or weight threshold. */
protected boolean evicts() {
return false;
}
/** Returns if entries may be assigned different weights. */
protected boolean isWeighted() {
return (weigher != Weigher.singletonWeigher());
}
protected FrequencySketch frequencySketch() {
throw new UnsupportedOperationException();
}
/** Returns if an access to an entry can skip notifying the eviction policy. */
protected boolean fastpath() {
return false;
}
/** Returns the maximum weighted size. */
protected long maximum() {
throw new UnsupportedOperationException();
}
/** Returns the maximum weighted size of the window space. */
protected long windowMaximum() {
throw new UnsupportedOperationException();
}
/** Returns the maximum weighted size of the main's protected space. */
protected long mainProtectedMaximum() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setMaximum(long maximum) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setWindowMaximum(long maximum) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setMainProtectedMaximum(long maximum) {
throw new UnsupportedOperationException();
}
/** Returns the combined weight of the values in the cache (may be negative). */
protected long weightedSize() {
throw new UnsupportedOperationException();
}
/** Returns the uncorrected combined weight of the values in the window space. */
protected long windowWeightedSize() {
throw new UnsupportedOperationException();
}
/** Returns the uncorrected combined weight of the values in the main's protected space. */
protected long mainProtectedWeightedSize() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setWeightedSize(long weightedSize) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setWindowWeightedSize(long weightedSize) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setMainProtectedWeightedSize(long weightedSize) {
throw new UnsupportedOperationException();
}
protected int hitsInSample() {
throw new UnsupportedOperationException();
}
protected int missesInSample() {
throw new UnsupportedOperationException();
}
protected int sampleCount() {
throw new UnsupportedOperationException();
}
protected double stepSize() {
throw new UnsupportedOperationException();
}
protected double previousSampleHitRate() {
throw new UnsupportedOperationException();
}
protected long adjustment() {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setHitsInSample(int hitCount) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setMissesInSample(int missCount) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setSampleCount(int sampleCount) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setStepSize(double stepSize) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setPreviousSampleHitRate(double hitRate) {
throw new UnsupportedOperationException();
}
@GuardedBy("evictionLock")
protected void setAdjustment(long amount) {
throw new UnsupportedOperationException();
}
/**
* Sets the maximum weighted size of the cache. The caller may need to perform a maintenance cycle
* to eagerly evicts entries until the cache shrinks to the appropriate size.
*/
@GuardedBy("evictionLock")
void setMaximumSize(long maximum) {
requireArgument(maximum >= 0, "maximum must not be negative");
if (maximum == maximum()) {
return;
}
long max = Math.min(maximum, MAXIMUM_CAPACITY);
long window = max - (long) (PERCENT_MAIN * max);
long mainProtected = (long) (PERCENT_MAIN_PROTECTED * (max - window));
setMaximum(max);
setWindowMaximum(window);
setMainProtectedMaximum(mainProtected);
setHitsInSample(0);
setMissesInSample(0);
setStepSize(-HILL_CLIMBER_STEP_PERCENT * max);
if ((frequencySketch() != null) && !isWeighted() && (weightedSize() >= (max >>> 1))) {
// Lazily initialize when close to the maximum size
frequencySketch().ensureCapacity(max);
}
}
/** Evicts entries if the cache exceeds the maximum. */
@GuardedBy("evictionLock")
void evictEntries() {
if (!evicts()) {
return;
}
int candidates = evictFromWindow();
evictFromMain(candidates);
}
/**
* Evicts entries from the window space into the main space while the window size exceeds a
* maximum.
*
* @return the number of candidate entries evicted from the window space
*/
@GuardedBy("evictionLock")
int evictFromWindow() {
int candidates = 0;
Node node = accessOrderWindowDeque().peek();
while (windowWeightedSize() > windowMaximum()) {
// The pending operations will adjust the size to reflect the correct weight
if (node == null) {
break;
}
Node next = node.getNextInAccessOrder();
if (node.getPolicyWeight() != 0) {
node.makeMainProbation();
accessOrderWindowDeque().remove(node);
accessOrderProbationDeque().add(node);
candidates++;
setWindowWeightedSize(windowWeightedSize() - node.getPolicyWeight());
}
node = next;
}
return candidates;
}
/**
* Evicts entries from the main space if the cache exceeds the maximum capacity. The main space
* determines whether admitting an entry (coming from the window space) is preferable to retaining
* the eviction policy's victim. This decision is made using a frequency filter so that the
* least frequently used entry is removed.
*
* The window space's candidates were previously placed in the MRU position and the eviction
* policy's victim is at the LRU position. The two ends of the queue are evaluated while an
* eviction is required. The number of remaining candidates is provided and decremented on
* eviction, so that when there are no more candidates the victim is evicted.
*
* @param candidates the number of candidate entries evicted from the window space
*/
@GuardedBy("evictionLock")
void evictFromMain(int candidates) {
int victimQueue = PROBATION;
Node victim = accessOrderProbationDeque().peekFirst();
Node candidate = accessOrderProbationDeque().peekLast();
while (weightedSize() > maximum()) {
// Search the admission window for additional candidates
if (candidates == 0) {
candidate = accessOrderWindowDeque().peekLast();
}
// Try evicting from the protected and window queues
if ((candidate == null) && (victim == null)) {
if (victimQueue == PROBATION) {
victim = accessOrderProtectedDeque().peekFirst();
victimQueue = PROTECTED;
continue;
} else if (victimQueue == PROTECTED) {
victim = accessOrderWindowDeque().peekFirst();
victimQueue = WINDOW;
continue;
}
// The pending operations will adjust the size to reflect the correct weight
break;
}
// Skip over entries with zero weight
if ((victim != null) && (victim.getPolicyWeight() == 0)) {
victim = victim.getNextInAccessOrder();
continue;
} else if ((candidate != null) && (candidate.getPolicyWeight() == 0)) {
candidate = (candidates > 0)
? candidate.getPreviousInAccessOrder()
: candidate.getNextInAccessOrder();
candidates--;
continue;
}
// Evict immediately if only one of the entries is present
if (victim == null) {
@SuppressWarnings("NullAway")
Node previous = candidate.getPreviousInAccessOrder();
Node evict = candidate;
candidate = previous;
candidates--;
evictEntry(evict, RemovalCause.SIZE, 0L);
continue;
} else if (candidate == null) {
Node evict = victim;
victim = victim.getNextInAccessOrder();
evictEntry(evict, RemovalCause.SIZE, 0L);
continue;
}
// Evict immediately if an entry was collected
K victimKey = victim.getKey();
K candidateKey = candidate.getKey();
if (victimKey == null) {
@NonNull Node evict = victim;
victim = victim.getNextInAccessOrder();
evictEntry(evict, RemovalCause.COLLECTED, 0L);
continue;
} else if (candidateKey == null) {
@NonNull Node evict = candidate;
candidate = (candidates > 0)
? candidate.getPreviousInAccessOrder()
: candidate.getNextInAccessOrder();
candidates--;
evictEntry(evict, RemovalCause.COLLECTED, 0L);
continue;
}
// Evict immediately if the candidate's weight exceeds the maximum
if (candidate.getPolicyWeight() > maximum()) {
Node evict = candidate;
candidate = (candidates > 0)
? candidate.getPreviousInAccessOrder()
: candidate.getNextInAccessOrder();
candidates--;
evictEntry(evict, RemovalCause.SIZE, 0L);
continue;
}
// Evict the entry with the lowest frequency
candidates--;
if (admit(candidateKey, victimKey)) {
Node evict = victim;
victim = victim.getNextInAccessOrder();
evictEntry(evict, RemovalCause.SIZE, 0L);
candidate = candidate.getPreviousInAccessOrder();
} else {
Node evict = candidate;
candidate = (candidates > 0)
? candidate.getPreviousInAccessOrder()
: candidate.getNextInAccessOrder();
evictEntry(evict, RemovalCause.SIZE, 0L);
}
}
}
/**
* Determines if the candidate should be accepted into the main space, as determined by its
* frequency relative to the victim. A small amount of randomness is used to protect against hash
* collision attacks, where the victim's frequency is artificially raised so that no new entries
* are admitted.
*
* @param candidateKey the key for the entry being proposed for long term retention
* @param victimKey the key for the entry chosen by the eviction policy for replacement
* @return if the candidate should be admitted and the victim ejected
*/
@GuardedBy("evictionLock")
boolean admit(K candidateKey, K victimKey) {
int victimFreq = frequencySketch().frequency(victimKey);
int candidateFreq = frequencySketch().frequency(candidateKey);
if (candidateFreq > victimFreq) {
return true;
} else if (candidateFreq <= 5) {
// The maximum frequency is 15 and halved to 7 after a reset to age the history. An attack
// exploits that a hot candidate is rejected in favor of a hot victim. The threshold of a warm
// candidate reduces the number of random acceptances to minimize the impact on the hit rate.
return false;
}
int random = ThreadLocalRandom.current().nextInt();
return ((random & 127) == 0);
}
/** Expires entries that have expired by access, write, or variable. */
@GuardedBy("evictionLock")
void expireEntries() {
long now = expirationTicker().read();
expireAfterAccessEntries(now);
expireAfterWriteEntries(now);
expireVariableEntries(now);
Pacer pacer = pacer();
if (pacer != null) {
long delay = getExpirationDelay(now);
if (delay == Long.MAX_VALUE) {
pacer.cancel();
} else {
pacer.schedule(executor, drainBuffersTask, now, delay);
}
}
}
/** Expires entries in the access-order queue. */
@GuardedBy("evictionLock")
void expireAfterAccessEntries(long now) {
if (!expiresAfterAccess()) {
return;
}
expireAfterAccessEntries(accessOrderWindowDeque(), now);
if (evicts()) {
expireAfterAccessEntries(accessOrderProbationDeque(), now);
expireAfterAccessEntries(accessOrderProtectedDeque(), now);
}
}
/** Expires entries in an access-order queue. */
@GuardedBy("evictionLock")
void expireAfterAccessEntries(AccessOrderDeque> accessOrderDeque, long now) {
long duration = expiresAfterAccessNanos();
for (;;) {
Node node = accessOrderDeque.peekFirst();
if ((node == null) || ((now - node.getAccessTime()) < duration)
|| !evictEntry(node, RemovalCause.EXPIRED, now)) {
return;
}
}
}
/** Expires entries on the write-order queue. */
@GuardedBy("evictionLock")
void expireAfterWriteEntries(long now) {
if (!expiresAfterWrite()) {
return;
}
long duration = expiresAfterWriteNanos();
for (;;) {
Node node = writeOrderDeque().peekFirst();
if ((node == null) || ((now - node.getWriteTime()) < duration)
|| !evictEntry(node, RemovalCause.EXPIRED, now)) {
break;
}
}
}
/** Expires entries in the timer wheel. */
@GuardedBy("evictionLock")
void expireVariableEntries(long now) {
if (expiresVariable()) {
timerWheel().advance(now);
}
}
/** Returns the duration until the next item expires, or {@link Long.MAX_VALUE} if none. */
@GuardedBy("evictionLock")
private long getExpirationDelay(long now) {
long delay = Long.MAX_VALUE;
if (expiresAfterAccess()) {
Node node = accessOrderWindowDeque().peekFirst();
if (node != null) {
delay = Math.min(delay, expiresAfterAccessNanos() - (now - node.getAccessTime()));
}
if (evicts()) {
node = accessOrderProbationDeque().peekFirst();
if (node != null) {
delay = Math.min(delay, expiresAfterAccessNanos() - (now - node.getAccessTime()));
}
node = accessOrderProtectedDeque().peekFirst();
if (node != null) {
delay = Math.min(delay, expiresAfterAccessNanos() - (now - node.getAccessTime()));
}
}
}
if (expiresAfterWrite()) {
Node node = writeOrderDeque().peekFirst();
if (node != null) {
delay = Math.min(delay, expiresAfterWriteNanos() - (now - node.getWriteTime()));
}
}
if (expiresVariable()) {
delay = Math.min(delay, timerWheel().getExpirationDelay());
}
return delay;
}
/** Returns if the entry has expired. */
@SuppressWarnings("ShortCircuitBoolean")
boolean hasExpired(Node node, long now) {
if (isComputingAsync(node)) {
return false;
}
return (expiresAfterAccess() && (now - node.getAccessTime() >= expiresAfterAccessNanos()))
| (expiresAfterWrite() && (now - node.getWriteTime() >= expiresAfterWriteNanos()))
| (expiresVariable() && (now - node.getVariableTime() >= 0));
}
/**
* Attempts to evict the entry based on the given removal cause. A removal due to may be ignored
* if the entry was updated and is no longer eligible for eviction.
*
* @param node the entry to evict
* @param cause the reason to evict
* @param now the current time, used only if expiring
* @return if the entry was evicted
*/
@GuardedBy("evictionLock")
@SuppressWarnings({"PMD.CollapsibleIfStatements", "GuardedByChecker", "NullAway"})
boolean evictEntry(Node node, RemovalCause cause, long now) {
K key = node.getKey();
@SuppressWarnings("unchecked")
V[] value = (V[]) new Object[1];
boolean[] removed = new boolean[1];
boolean[] resurrect = new boolean[1];
RemovalCause[] actualCause = new RemovalCause[1];
data.computeIfPresent(node.getKeyReference(), (k, n) -> {
if (n != node) {
return n;
}
synchronized (n) {
value[0] = n.getValue();
if ((key == null) || (value[0] == null)) {
actualCause[0] = RemovalCause.COLLECTED;
} else if (cause == RemovalCause.COLLECTED) {
resurrect[0] = true;
return n;
} else {
actualCause[0] = cause;
}
if (actualCause[0] == RemovalCause.EXPIRED) {
boolean expired = false;
if (expiresAfterAccess()) {
expired |= ((now - n.getAccessTime()) >= expiresAfterAccessNanos());
}
if (expiresAfterWrite()) {
expired |= ((now - n.getWriteTime()) >= expiresAfterWriteNanos());
}
if (expiresVariable()) {
expired |= (n.getVariableTime() <= now);
}
if (!expired) {
resurrect[0] = true;
return n;
}
} else if (actualCause[0] == RemovalCause.SIZE) {
int weight = node.getWeight();
if (weight == 0) {
resurrect[0] = true;
return n;
}
}
writer.delete(key, value[0], actualCause[0]);
makeDead(n);
}
removed[0] = true;
return null;
});
// The entry is no longer eligible for eviction
if (resurrect[0]) {
return false;
}
// If the eviction fails due to a concurrent removal of the victim, that removal may cancel out
// the addition that triggered this eviction. The victim is eagerly unlinked before the removal
// task so that if an eviction is still required then a new victim will be chosen for removal.
if (node.inWindow() && (evicts() || expiresAfterAccess())) {
accessOrderWindowDeque().remove(node);
} else if (evicts()) {
if (node.inMainProbation()) {
accessOrderProbationDeque().remove(node);
} else {
accessOrderProtectedDeque().remove(node);
}
}
if (expiresAfterWrite()) {
writeOrderDeque().remove(node);
} else if (expiresVariable()) {
timerWheel().deschedule(node);
}
if (removed[0]) {
statsCounter().recordEviction(node.getWeight(), actualCause[0]);
if (hasRemovalListener()) {
// Notify the listener only if the entry was evicted. This must be performed as the last
// step during eviction to safe guard against the executor rejecting the notification task.
notifyRemoval(key, value[0], actualCause[0]);
}
} else {
// Eagerly decrement the size to potentially avoid an additional eviction, rather than wait
// for the removal task to do it on the next maintenance cycle.
makeDead(node);
}
return true;
}
/** Adapts the eviction policy to towards the optimal recency / frequency configuration. */
@GuardedBy("evictionLock")
void climb() {
if (!evicts()) {
return;
}
determineAdjustment();
demoteFromMainProtected();
long amount = adjustment();
if (amount == 0) {
return;
} else if (amount > 0) {
increaseWindow();
} else {
decreaseWindow();
}
}
/** Calculates the amount to adapt the window by and sets {@link #adjustment()} accordingly. */
@GuardedBy("evictionLock")
void determineAdjustment() {
if (frequencySketch().isNotInitialized()) {
setPreviousSampleHitRate(0.0);
setMissesInSample(0);
setHitsInSample(0);
return;
}
int requestCount = hitsInSample() + missesInSample();
if (requestCount < frequencySketch().sampleSize) {
return;
}
double hitRate = (double) hitsInSample() / requestCount;
double hitRateChange = hitRate - previousSampleHitRate();
double amount = (hitRateChange >= 0) ? stepSize() : -stepSize();
double nextStepSize = (Math.abs(hitRateChange) >= HILL_CLIMBER_RESTART_THRESHOLD)
? HILL_CLIMBER_STEP_PERCENT * maximum() * (amount >= 0 ? 1 : -1)
: HILL_CLIMBER_STEP_DECAY_RATE * amount;
setPreviousSampleHitRate(hitRate);
setAdjustment((long) amount);
setStepSize(nextStepSize);
setMissesInSample(0);
setHitsInSample(0);
}
/**
* Increases the size of the admission window by shrinking the portion allocated to the main
* space. As the main space is partitioned into probation and protected regions (80% / 20%), for
* simplicity only the protected is reduced. If the regions exceed their maximums, this may cause
* protected items to be demoted to the probation region and probation items to be demoted to the
* admission window.
*/
@GuardedBy("evictionLock")
void increaseWindow() {
if (mainProtectedMaximum() == 0) {
return;
}
long quota = Math.min(adjustment(), mainProtectedMaximum());
setMainProtectedMaximum(mainProtectedMaximum() - quota);
setWindowMaximum(windowMaximum() + quota);
demoteFromMainProtected();
for (int i = 0; i < QUEUE_TRANSFER_THRESHOLD; i++) {
Node candidate = accessOrderProbationDeque().peek();
boolean probation = true;
if ((candidate == null) || (quota < candidate.getPolicyWeight())) {
candidate = accessOrderProtectedDeque().peek();
probation = false;
}
if (candidate == null) {
break;
}
int weight = candidate.getPolicyWeight();
if (quota < weight) {
break;
}
quota -= weight;
if (probation) {
accessOrderProbationDeque().remove(candidate);
} else {
setMainProtectedWeightedSize(mainProtectedWeightedSize() - weight);
accessOrderProtectedDeque().remove(candidate);
}
setWindowWeightedSize(windowWeightedSize() + weight);
accessOrderWindowDeque().add(candidate);
candidate.makeWindow();
}
setMainProtectedMaximum(mainProtectedMaximum() + quota);
setWindowMaximum(windowMaximum() - quota);
setAdjustment(quota);
}
/** Decreases the size of the admission window and increases the main's protected region. */
@GuardedBy("evictionLock")
void decreaseWindow() {
if (windowMaximum() <= 1) {
return;
}
long quota = Math.min(-adjustment(), Math.max(0, windowMaximum() - 1));
setMainProtectedMaximum(mainProtectedMaximum() + quota);
setWindowMaximum(windowMaximum() - quota);
for (int i = 0; i < QUEUE_TRANSFER_THRESHOLD; i++) {
Node candidate = accessOrderWindowDeque().peek();
if (candidate == null) {
break;
}
int weight = candidate.getPolicyWeight();
if (quota < weight) {
break;
}
quota -= weight;
setWindowWeightedSize(windowWeightedSize() - weight);
accessOrderWindowDeque().remove(candidate);
accessOrderProbationDeque().add(candidate);
candidate.makeMainProbation();
}
setMainProtectedMaximum(mainProtectedMaximum() - quota);
setWindowMaximum(windowMaximum() + quota);
setAdjustment(-quota);
}
/** Transfers the nodes from the protected to the probation region if it exceeds the maximum. */
@GuardedBy("evictionLock")
void demoteFromMainProtected() {
long mainProtectedMaximum = mainProtectedMaximum();
long mainProtectedWeightedSize = mainProtectedWeightedSize();
if (mainProtectedWeightedSize <= mainProtectedMaximum) {
return;
}
for (int i = 0; i < QUEUE_TRANSFER_THRESHOLD; i++) {
if (mainProtectedWeightedSize <= mainProtectedMaximum) {
break;
}
Node demoted = accessOrderProtectedDeque().poll();
if (demoted == null) {
break;
}
demoted.makeMainProbation();
accessOrderProbationDeque().add(demoted);
mainProtectedWeightedSize -= demoted.getPolicyWeight();
}
setMainProtectedWeightedSize(mainProtectedWeightedSize);
}
/**
* Performs the post-processing work required after a read.
*
* @param node the entry in the page replacement policy
* @param now the current time, in nanoseconds
* @param recordHit if the hit count should be incremented
*/
void afterRead(Node node, long now, boolean recordHit) {
if (recordHit) {
statsCounter().recordHits(1);
}
boolean delayable = skipReadBuffer() || (readBuffer.offer(node) != Buffer.FULL);
if (shouldDrainBuffers(delayable)) {
scheduleDrainBuffers();
}
refreshIfNeeded(node, now);
}
/** Returns if the cache should bypass the read buffer. */
boolean skipReadBuffer() {
return fastpath() && frequencySketch().isNotInitialized();
}
/**
* Asynchronously refreshes the entry if eligible.
*
* @param node the entry in the cache to refresh
* @param now the current time, in nanoseconds
*/
@SuppressWarnings("FutureReturnValueIgnored")
void refreshIfNeeded(Node node, long now) {
if (!refreshAfterWrite()) {
return;
}
K key;
V oldValue;
long oldWriteTime = node.getWriteTime();
long refreshWriteTime = (now + ASYNC_EXPIRY);
if (((now - oldWriteTime) > refreshAfterWriteNanos())
&& ((key = node.getKey()) != null) && ((oldValue = node.getValue()) != null)
&& node.casWriteTime(oldWriteTime, refreshWriteTime)) {
try {
CompletableFuture refreshFuture;
long startTime = statsTicker().read();
if (isAsync) {
@SuppressWarnings("unchecked")
CompletableFuture future = (CompletableFuture) oldValue;
if (Async.isReady(future)) {
@SuppressWarnings("NullAway")
CompletableFuture refresh = future.thenCompose(value ->
cacheLoader.asyncReload(key, value, executor));
refreshFuture = refresh;
} else {
// no-op if load is pending
node.casWriteTime(refreshWriteTime, oldWriteTime);
return;
}
} else {
@SuppressWarnings("NullAway")
CompletableFuture refresh = cacheLoader.asyncReload(key, oldValue, executor);
refreshFuture = refresh;
}
refreshFuture.whenComplete((newValue, error) -> {
long loadTime = statsTicker().read() - startTime;
if (error != null) {
if (!(error instanceof CancellationException) && !(error instanceof TimeoutException)) {
logger.log(Level.WARNING, "Exception thrown during refresh", error);
}
node.casWriteTime(refreshWriteTime, oldWriteTime);
statsCounter().recordLoadFailure(loadTime);
return;
}
@SuppressWarnings("unchecked")
V value = (isAsync && (newValue != null)) ? (V) refreshFuture : newValue;
boolean[] discard = new boolean[1];
compute(key, (k, currentValue) -> {
if (currentValue == null) {
return value;
} else if ((currentValue == oldValue) && (node.getWriteTime() == refreshWriteTime)) {
return value;
}
discard[0] = true;
return currentValue;
}, /* recordMiss */ false, /* recordLoad */ false, /* recordLoadFailure */ true);
if (discard[0] && hasRemovalListener()) {
notifyRemoval(key, value, RemovalCause.REPLACED);
}
if (newValue == null) {
statsCounter().recordLoadFailure(loadTime);
} else {
statsCounter().recordLoadSuccess(loadTime);
}
});
} catch (Throwable t) {
node.casWriteTime(refreshWriteTime, oldWriteTime);
logger.log(Level.SEVERE, "Exception thrown when submitting refresh task", t);
}
}
}
/**
* Returns the expiration time for the entry after being created.
*
* @param key the key of the entry that was created
* @param value the value of the entry that was created
* @param expiry the calculator for the expiration time
* @param now the current time, in nanoseconds
* @return the expiration time
*/
long expireAfterCreate(@Nullable K key, @Nullable V value, Expiry expiry, long now) {
if (expiresVariable() && (key != null) && (value != null)) {
long duration = expiry.expireAfterCreate(key, value, now);
return isAsync ? (now + duration) : (now + Math.min(duration, MAXIMUM_EXPIRY));
}
return 0L;
}
/**
* Returns the expiration time for the entry after being updated.
*
* @param node the entry in the page replacement policy
* @param key the key of the entry that was updated
* @param value the value of the entry that was updated
* @param expiry the calculator for the expiration time
* @param now the current time, in nanoseconds
* @return the expiration time
*/
long expireAfterUpdate(Node node, @Nullable K key,
@Nullable V value, Expiry expiry, long now) {
if (expiresVariable() && (key != null) && (value != null)) {
long currentDuration = Math.max(1, node.getVariableTime() - now);
long duration = expiry.expireAfterUpdate(key, value, now, currentDuration);
return isAsync ? (now + duration) : (now + Math.min(duration, MAXIMUM_EXPIRY));
}
return 0L;
}
/**
* Returns the access time for the entry after a read.
*
* @param node the entry in the page replacement policy
* @param key the key of the entry that was read
* @param value the value of the entry that was read
* @param expiry the calculator for the expiration time
* @param now the current time, in nanoseconds
* @return the expiration time
*/
long expireAfterRead(Node node, @Nullable K key,
@Nullable V value, Expiry expiry, long now) {
if (expiresVariable() && (key != null) && (value != null)) {
long currentDuration = Math.max(1, node.getVariableTime() - now);
long duration = expiry.expireAfterRead(key, value, now, currentDuration);
return isAsync ? (now + duration) : (now + Math.min(duration, MAXIMUM_EXPIRY));
}
return 0L;
}
/**
* Attempts to update the access time for the entry after a read.
*
* @param node the entry in the page replacement policy
* @param key the key of the entry that was read
* @param value the value of the entry that was read
* @param expiry the calculator for the expiration time
* @param now the current time, in nanoseconds
*/
void tryExpireAfterRead(Node node, @Nullable K key,
@Nullable V value, Expiry expiry, long now) {
if (!expiresVariable() || (key == null) || (value == null)) {
return;
}
long variableTime = node.getVariableTime();
long currentDuration = Math.max(1, variableTime - now);
if (isAsync && (currentDuration > MAXIMUM_EXPIRY)) {
// expireAfterCreate has not yet set the duration after completion
return;
}
long duration = expiry.expireAfterRead(key, value, now, currentDuration);
if (duration != currentDuration) {
long expirationTime = isAsync ? (now + duration) : (now + Math.min(duration, MAXIMUM_EXPIRY));
node.casVariableTime(variableTime, expirationTime);
}
}
void setVariableTime(Node node, long expirationTime) {
if (expiresVariable()) {
node.setVariableTime(expirationTime);
}
}
void setWriteTime(Node node, long now) {
if (expiresAfterWrite() || refreshAfterWrite()) {
node.setWriteTime(now);
}
}
void setAccessTime(Node node, long now) {
if (expiresAfterAccess()) {
node.setAccessTime(now);
}
}
/**
* Performs the post-processing work required after a write.
*
* @param task the pending operation to be applied
*/
void afterWrite(Runnable task) {
for (int i = 0; i < WRITE_BUFFER_RETRIES; i++) {
if (writeBuffer.offer(task)) {
scheduleAfterWrite();
return;
}
scheduleDrainBuffers();
}
// The maintenance task may be scheduled but not running. This might occur due to all of the
// executor's threads being busy (perhaps writing into this cache), the write rate greatly
// exceeds the consuming rate, priority inversion, or if the executor silently discarded the
// maintenance task. In these scenarios then the writing threads cannot make progress and
// instead writers provide assistance by performing this work directly.
try {
performCleanUp(task);
} catch (RuntimeException e) {
logger.log(Level.SEVERE, "Exception thrown when performing the maintenance task", e);
}
}
/**
* Conditionally schedules the asynchronous maintenance task after a write operation. If the
* task status was IDLE or REQUIRED then the maintenance task is scheduled immediately. If it
* is already processing then it is set to transition to REQUIRED upon completion so that a new
* execution is triggered by the next operation.
*/
void scheduleAfterWrite() {
for (;;) {
switch (drainStatus()) {
case IDLE:
casDrainStatus(IDLE, REQUIRED);
scheduleDrainBuffers();
return;
case REQUIRED:
scheduleDrainBuffers();
return;
case PROCESSING_TO_IDLE:
if (casDrainStatus(PROCESSING_TO_IDLE, PROCESSING_TO_REQUIRED)) {
return;
}
continue;
case PROCESSING_TO_REQUIRED:
return;
default:
throw new IllegalStateException();
}
}
}
/**
* Attempts to schedule an asynchronous task to apply the pending operations to the page
* replacement policy. If the executor rejects the task then it is run directly.
*/
void scheduleDrainBuffers() {
if (drainStatus() >= PROCESSING_TO_IDLE) {
return;
}
if (evictionLock.tryLock()) {
try {
int drainStatus = drainStatus();
if (drainStatus >= PROCESSING_TO_IDLE) {
return;
}
lazySetDrainStatus(PROCESSING_TO_IDLE);
executor.execute(drainBuffersTask);
} catch (Throwable t) {
logger.log(Level.WARNING, "Exception thrown when submitting maintenance task", t);
maintenance(/* ignored */ null);
} finally {
evictionLock.unlock();
}
}
}
@Override
public void cleanUp() {
try {
performCleanUp(/* ignored */ null);
} catch (RuntimeException e) {
logger.log(Level.SEVERE, "Exception thrown when performing the maintenance task", e);
}
}
/**
* Performs the maintenance work, blocking until the lock is acquired. Any exception thrown, such
* as by {@link CacheWriter#delete}, is propagated to the caller.
*
* @param task an additional pending task to run, or {@code null} if not present
*/
void performCleanUp(@Nullable Runnable task) {
evictionLock.lock();
try {
maintenance(task);
} finally {
evictionLock.unlock();
}
if ((drainStatus() == REQUIRED) && (executor == ForkJoinPool.commonPool())) {
scheduleDrainBuffers();
}
}
/**
* Performs the pending maintenance work and sets the state flags during processing to avoid
* excess scheduling attempts. The read buffer, write buffer, and reference queues are
* drained, followed by expiration, and size-based eviction.
*
* @param task an additional pending task to run, or {@code null} if not present
*/
@GuardedBy("evictionLock")
void maintenance(@Nullable Runnable task) {
lazySetDrainStatus(PROCESSING_TO_IDLE);
try {
drainReadBuffer();
drainWriteBuffer();
if (task != null) {
task.run();
}
drainKeyReferences();
drainValueReferences();
expireEntries();
evictEntries();
climb();
} finally {
if ((drainStatus() != PROCESSING_TO_IDLE) || !casDrainStatus(PROCESSING_TO_IDLE, IDLE)) {
lazySetDrainStatus(REQUIRED);
}
}
}
/** Drains the weak key references queue. */
@GuardedBy("evictionLock")
void drainKeyReferences() {
if (!collectKeys()) {
return;
}
Reference keyRef;
while ((keyRef = keyReferenceQueue().poll()) != null) {
Node node = data.get(keyRef);
if (node != null) {
evictEntry(node, RemovalCause.COLLECTED, 0L);
}
}
}
/** Drains the weak / soft value references queue. */
@GuardedBy("evictionLock")
void drainValueReferences() {
if (!collectValues()) {
return;
}
Reference valueRef;
while ((valueRef = valueReferenceQueue().poll()) != null) {
@SuppressWarnings("unchecked")
InternalReference ref = (InternalReference) valueRef;
Node node = data.get(ref.getKeyReference());
if ((node != null) && (valueRef == node.getValueReference())) {
evictEntry(node, RemovalCause.COLLECTED, 0L);
}
}
}
/** Drains the read buffer. */
@GuardedBy("evictionLock")
void drainReadBuffer() {
if (!skipReadBuffer()) {
readBuffer.drainTo(accessPolicy);
}
}
/** Updates the node's location in the page replacement policy. */
@GuardedBy("evictionLock")
void onAccess(Node node) {
if (evicts()) {
K key = node.getKey();
if (key == null) {
return;
}
frequencySketch().increment(key);
if (node.inWindow()) {
reorder(accessOrderWindowDeque(), node);
} else if (node.inMainProbation()) {
reorderProbation(node);
} else {
reorder(accessOrderProtectedDeque(), node);
}
setHitsInSample(hitsInSample() + 1);
} else if (expiresAfterAccess()) {
reorder(accessOrderWindowDeque(), node);
}
if (expiresVariable()) {
timerWheel().reschedule(node);
}
}
/** Promote the node from probation to protected on an access. */
@GuardedBy("evictionLock")
void reorderProbation(Node node) {
if (!accessOrderProbationDeque().contains(node)) {
// Ignore stale accesses for an entry that is no longer present
return;
} else if (node.getPolicyWeight() > mainProtectedMaximum()) {
return;
}
// If the protected space exceeds its maximum, the LRU items are demoted to the probation space.
// This is deferred to the adaption phase at the end of the maintenance cycle.
setMainProtectedWeightedSize(mainProtectedWeightedSize() + node.getPolicyWeight());
accessOrderProbationDeque().remove(node);
accessOrderProtectedDeque().add(node);
node.makeMainProtected();
}
/** Updates the node's location in the policy's deque. */
static void reorder(LinkedDeque> deque, Node node) {
// An entry may be scheduled for reordering despite having been removed. This can occur when the
// entry was concurrently read while a writer was removing it. If the entry is no longer linked
// then it does not need to be processed.
if (deque.contains(node)) {
deque.moveToBack(node);
}
}
/** Drains the write buffer. */
@GuardedBy("evictionLock")
void drainWriteBuffer() {
for (int i = 0; i <= WRITE_BUFFER_MAX; i++) {
Runnable task = writeBuffer.poll();
if (task == null) {
return;
}
task.run();
}
lazySetDrainStatus(PROCESSING_TO_REQUIRED);
}
/**
* Atomically transitions the node to the dead state and decrements the
* weightedSize.
*
* @param node the entry in the page replacement policy
*/
@GuardedBy("evictionLock")
void makeDead(Node node) {
synchronized (node) {
if (node.isDead()) {
return;
}
if (evicts()) {
// The node's policy weight may be out of sync due to a pending update waiting to be
// processed. At this point the node's weight is finalized, so the weight can be safely
// taken from the node's perspective and the sizes will be adjusted correctly.
if (node.inWindow()) {
setWindowWeightedSize(windowWeightedSize() - node.getWeight());
} else if (node.inMainProtected()) {
setMainProtectedWeightedSize(mainProtectedWeightedSize() - node.getWeight());
}
setWeightedSize(weightedSize() - node.getWeight());
}
node.die();
}
}
/** Adds the node to the page replacement policy. */
final class AddTask implements Runnable {
final Node node;
final int weight;
AddTask(Node node, int weight) {
this.weight = weight;
this.node = node;
}
@Override
@GuardedBy("evictionLock")
@SuppressWarnings("FutureReturnValueIgnored")
public void run() {
if (evicts()) {
long weightedSize = weightedSize();
setWeightedSize(weightedSize + weight);
setWindowWeightedSize(windowWeightedSize() + weight);
node.setPolicyWeight(node.getPolicyWeight() + weight);
long maximum = maximum();
if (weightedSize >= (maximum >>> 1)) {
// Lazily initialize when close to the maximum
long capacity = isWeighted() ? data.mappingCount() : maximum;
frequencySketch().ensureCapacity(capacity);
}
K key = node.getKey();
if (key != null) {
frequencySketch().increment(key);
}
setMissesInSample(missesInSample() + 1);
}
// ignore out-of-order write operations
boolean isAlive;
synchronized (node) {
isAlive = node.isAlive();
}
if (isAlive) {
if (expiresAfterWrite()) {
writeOrderDeque().add(node);
}
if (evicts() && (weight > windowMaximum())) {
accessOrderWindowDeque().offerFirst(node);
} else if (evicts() || expiresAfterAccess()) {
accessOrderWindowDeque().offerLast(node);
}
if (expiresVariable()) {
timerWheel().schedule(node);
}
}
// Ensure that in-flight async computation cannot expire (reset on a completion callback)
if (isComputingAsync(node)) {
synchronized (node) {
if (!Async.isReady((CompletableFuture) node.getValue())) {
long expirationTime = expirationTicker().read() + ASYNC_EXPIRY;
setVariableTime(node, expirationTime);
setAccessTime(node, expirationTime);
setWriteTime(node, expirationTime);
}
}
}
}
}
/** Removes a node from the page replacement policy. */
final class RemovalTask implements Runnable {
final Node node;
RemovalTask(Node node) {
this.node = node;
}
@Override
@GuardedBy("evictionLock")
public void run() {
// add may not have been processed yet
if (node.inWindow() && (evicts() || expiresAfterAccess())) {
accessOrderWindowDeque().remove(node);
} else if (evicts()) {
if (node.inMainProbation()) {
accessOrderProbationDeque().remove(node);
} else {
accessOrderProtectedDeque().remove(node);
}
}
if (expiresAfterWrite()) {
writeOrderDeque().remove(node);
} else if (expiresVariable()) {
timerWheel().deschedule(node);
}
makeDead(node);
}
}
/** Updates the weighted size. */
final class UpdateTask implements Runnable {
final int weightDifference;
final Node node;
public UpdateTask(Node node, int weightDifference) {
this.weightDifference = weightDifference;
this.node = node;
}
@Override
@GuardedBy("evictionLock")
public void run() {
if (evicts()) {
int oldWeightedSize = node.getPolicyWeight();
node.setPolicyWeight(oldWeightedSize + weightDifference);
if (node.inWindow()) {
if (node.getPolicyWeight() <= windowMaximum()) {
onAccess(node);
} else if (accessOrderWindowDeque().contains(node)) {
accessOrderWindowDeque().moveToFront(node);
}
setWindowWeightedSize(windowWeightedSize() + weightDifference);
} else if (node.inMainProbation()) {
if (node.getPolicyWeight() <= maximum()) {
onAccess(node);
} else if (accessOrderProbationDeque().remove(node)) {
accessOrderWindowDeque().addFirst(node);
setWindowWeightedSize(windowWeightedSize() + node.getPolicyWeight());
}
} else if (node.inMainProtected()) {
if (node.getPolicyWeight() <= maximum()) {
onAccess(node);
setMainProtectedWeightedSize(mainProtectedWeightedSize() + weightDifference);
} else if (accessOrderProtectedDeque().remove(node)) {
accessOrderWindowDeque().addFirst(node);
setWindowWeightedSize(windowWeightedSize() + node.getPolicyWeight());
setMainProtectedWeightedSize(mainProtectedWeightedSize() - oldWeightedSize);
} else {
setMainProtectedWeightedSize(mainProtectedWeightedSize() - oldWeightedSize);
}
}
setWeightedSize(weightedSize() + weightDifference);
} else if (expiresAfterAccess()) {
onAccess(node);
}
if (expiresAfterWrite()) {
reorder(writeOrderDeque(), node);
} else if (expiresVariable()) {
timerWheel().reschedule(node);
}
}
}
/* --------------- Concurrent Map Support --------------- */
@Override
public boolean isEmpty() {
return data.isEmpty();
}
@Override
public int size() {
return data.size();
}
@Override
public long estimatedSize() {
return data.mappingCount();
}
@Override
@SuppressWarnings("FutureReturnValueIgnored")
public void clear() {
evictionLock.lock();
try {
long now = expirationTicker().read();
// Apply all pending writes
Runnable task;
while ((task = writeBuffer.poll()) != null) {
task.run();
}
// Discard all entries
for (Node node : data.values()) {
removeNode(node, now);
}
// Cancel the scheduled cleanup
Pacer pacer = pacer();
if (pacer != null) {
pacer.cancel();
}
// Discard all pending reads
readBuffer.drainTo(e -> {});
} finally {
evictionLock.unlock();
}
}
@GuardedBy("evictionLock")
@SuppressWarnings("GuardedByChecker")
void removeNode(Node node, long now) {
K key = node.getKey();
@SuppressWarnings("unchecked")
V[] value = (V[]) new Object[1];
RemovalCause[] cause = new RemovalCause[1];
data.computeIfPresent(node.getKeyReference(), (k, n) -> {
if (n != node) {
return n;
}
synchronized (n) {
value[0] = n.getValue();
if ((key == null) || (value[0] == null)) {
cause[0] = RemovalCause.COLLECTED;
} else if (hasExpired(n, now)) {
cause[0] = RemovalCause.EXPIRED;
} else {
cause[0] = RemovalCause.EXPLICIT;
}
if (key != null) {
writer.delete(key, value[0], cause[0]);
}
makeDead(n);
return null;
}
});
if (node.inWindow() && (evicts() || expiresAfterAccess())) {
accessOrderWindowDeque().remove(node);
} else if (evicts()) {
if (node.inMainProbation()) {
accessOrderProbationDeque().remove(node);
} else {
accessOrderProtectedDeque().remove(node);
}
}
if (expiresAfterWrite()) {
writeOrderDeque().remove(node);
} else if (expiresVariable()) {
timerWheel().deschedule(node);
}
if ((cause[0] != null) && hasRemovalListener()) {
notifyRemoval(key, value[0], cause[0]);
}
}
@Override
public boolean containsKey(Object key) {
Node node = data.get(nodeFactory.newLookupKey(key));
return (node != null) && (node.getValue() != null)
&& !hasExpired(node, expirationTicker().read());
}
@Override
public boolean containsValue(Object value) {
requireNonNull(value);
long now = expirationTicker().read();
for (Node node : data.values()) {
if (node.containsValue(value) && !hasExpired(node, now) && (node.getKey() != null)) {
return true;
}
}
return false;
}
@Override
public @Nullable V get(Object key) {
return getIfPresent(key, /* recordStats */ false);
}
@Override
public @Nullable V getIfPresent(Object key, boolean recordStats) {
Node node = data.get(nodeFactory.newLookupKey(key));
if (node == null) {
if (recordStats) {
statsCounter().recordMisses(1);
}
if (drainStatus() == REQUIRED) {
scheduleDrainBuffers();
}
return null;
}
V value = node.getValue();
long now = expirationTicker().read();
if (hasExpired(node, now) || (collectValues() && (value == null))) {
if (recordStats) {
statsCounter().recordMisses(1);
}
scheduleDrainBuffers();
return null;
}
if (!isComputingAsync(node)) {
@SuppressWarnings("unchecked")
K castedKey = (K) key;
setAccessTime(node, now);
tryExpireAfterRead(node, castedKey, value, expiry(), now);
}
afterRead(node, now, recordStats);
return value;
}
@Override
public @Nullable V getIfPresentQuietly(Object key, long[/* 1 */] writeTime) {
V value;
Node node = data.get(nodeFactory.newLookupKey(key));
if ((node == null) || ((value = node.getValue()) == null)
|| hasExpired(node, expirationTicker().read())) {
return null;
}
writeTime[0] = node.getWriteTime();
return value;
}
@Override
public Map getAllPresent(Iterable keys) {
Set